General Definitions Electrical

8/8/2019 General Definitions Electrical

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y Class Vocabulary

branch circuit The part of a distribution system consisting of circuit conductors, between the final overcurrent protection and the outlet orload attached.

busbar Thick, rigid strips or bars of copper that serve as a common connection between several circuits. Busbars are usually usednear the switchboard and can be enclosed in busways.

busway The part of a distribution system consisting of metal enclosed busbars. Busways come in premade sections that can be fitted

to any shape needed.center tap The point where all three windings are connected to each other in a wye connection. For delta connections, one of the lines

must be tapped to produce a neutral.

copper loss A power loss due to current flowing through wire. Copper loss is proportional to the resistance of the wire and the square ofthe current.

core A component of a transformer. The iron or steel core provides a controlled path for the magnetic flux generated in thetransformer by the current flowing through the windings.

delta A connection of three components where a triangular series circuit is formed. Delta connections are used in three phasepower systems.

delta/delta A transformer with both the primary and the secondary connected as a delta.

delta/wye A transformer with the primary connected as a delta and the secondary connected as a wye.

distribution substation A bank of step-down transformers near the end users. The distribution substation converts voltage closer to the requiredusable levels.

distribution system A circuit of users linked to a generating station and substations that is typically arranged in either a radial or interconnectedmanner. Local distribution systems transport power within a building.

enclosure A physical barrier designed to provide mechanical or electrical protection for components used in a system.feeder A circuit conductor between the power supply source and a final branch circuit overcurrent device.

generating station A building where a utility company houses large linked AC generators to create the massive power for widespread use.

grounded conductor A system conductor that is intentionally grounded.

grounding conductor A conductor used to connect equipment in a wiring system to ground.

interconnected system A distribution system with multiple available power sources that can loop throughout the network. If one source goes down, adifferent source can be activated to maintain service.

kilovolt-amp A unit used to rate transformer and generator strength. A kilovolt is a thousand volts.

laminated Sealed together in multiple layers of thin sheets to construct the core for a transformer. Lamination helps reduce resistancelosses.

line voltage The voltage present between any two of the conductors in a three-phase system. It is 1.732 times higher than phase voltagein a wye connection.

load center A device found in residential locations that performs the same functions as a panelboard does in commercial settings. Loadcenters are not required to have many panelboard safety features because homes do not draw the same amount of current asindustry.

local power distribution system The part of a distribution system located within a building. Local distribution systems are the responsibility of shopelectricians and maintenance workers and fall under NEC rules.

main disconnect switch A heavy, spring-loaded switch on a factory switchboard that can cut off power to the entire building. Switchboards with morethan six switches or breakers are required by the NEC to have a main disconnect.

motor control center A modular assembly specifically designed to plug in motor control units. Motor control centers are supplied by a common bus,usually straight from the switchboard.

mutual induction The ability of one coil to induce a voltage into another coil. This principle is used in transformers to step up or step downvoltage.

NEC The standard for minimum safe electrical installations. The National Electrical Code is adopted in some form as law in all 50states.

network system A distribution system where multiple power sources are connected to each user to guarantee uninterrupted power. A networksystem is expensive, so it is used only when constant power is vital.

open delta A transformer connection that does not complete the triangle, using only two of the three sides. An open delta is used whenfull power is not needed.

overcurrent Excess current that may result from overload, short circuit, or ground fault. Devices like fuses and circuit breakers protectagainst overcurrent.

panelboard A single panel distribution cabinet or wall cutout box that holds automatic overcurrent protection devices for lighting, heat,or power circuits.

phase symbol () The Greek letter Phi, used to represent phases, such as in a 34W system.

phase voltage The voltage between any one conductor and ground.

plug-in busway A type of feeder busway with electrical control that allows loads to be added along the bus structure.

primary winding Turns of wire on a transformer core, used to transfer voltage from the input to the core.

radial system A distribution system with only one power source. If that source goes out, power is lost to the entire circuit.

revolving field generator A generator setup where an electromagnetic field is rotated between the conductor wound armature. Most AC generators areof this design.



Class Vocabulary

secondary winding Turns of wire on a transformer core, used to transfer voltage from the core to the outside load.

service-entrance The point where electricity enters a buidling. A service-entrance switchboard has metering equipment and devices forovercurrent protection and electrical control.

single-phase A continuous single alternating current cycle.

step up In electricity, a phrase used to describe voltage adjustment. To step up voltage means to increase voltage.

substation Any grouping of switchgear and transformers located near a source or user. Substations are used to alter voltage levels andprovide a service point of electrical control.

switchboard A freestanding assembly of panels with metering equipment, overcurrent and other protection devices. Switchboards take alarge block of power from a substation and break it down into smaller blocks for use within a building.

switchgear A combination of disconnect switches and breakers used to isolate equipment in substations.

tap A wire connected to the midpoint of a transformer secondary winding. This allows the transformer to use different turnsratios.

terminal A connecting point in a circuit where a wire is attached to create an electrical connection.

three-phase A continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large scaledistribution systems.

three-phase power The most common form of AC power for distribution. Three-phase power has three overlapping AC cycles offset by 120degrees.

transformer A device that transfers electrical energy from one circuit to another, without changing the frequency, using electromagneticinduction. A transformer is most often used to change the line voltage.

transmission substation A bank of step up transformers near the generating station. Transmission substations increase voltage as high as 800kV forwidespread distribution.

turns ratio A comparison of the number of turns in the primary versus the number of turns in the secondary of a transformer.

wye A connection of three components where one end of each component is connected at a common point. Wye connections areused in three phase power systems.

wye/delta A transformer with the primary connected as a wye and the secondary connected as a delta.

wye/wye A transformer with both the primary and the secondary connected as a wye

air flow switch A type of flow switch that detects the movement of air. The air flow switch symbol has a flag shape that represents a sail.

alternating current Current that regularly reverses the direction of its flow in a repeating, cyclical pattern.

armature The part of a motor in which a current is induced by a magnetic field. The armature usually consists of a series of coils orgroups of insulated conductors surrounding a core of iron.

bimetal strip A strip made by bonding together two unlike metals that expand at different rates when heated.

bumper arm A physical device on a limit switch that makes contact with an object causing the contact of the switch to change position.

circuit breaker A safety device that detects too much current in a circuit. A circuit breaker often contains a bimetallic strip that bends andtrips a switch that opens a circuit.

coil A wound spiral of two or more turns of wire used to conduct current.

compound motor A DC motor that uses both series and shunt field windings. Compound motors combine the advantages of the shunt and seriesmotors.

constant speed motor A type of motor that maintains a steady rate of rpm from no load to full load. DC shunt motors are often referred to asconstant speed motors because they have this characteristic.

contact A conductive part in an electrical circuit attached to a switch that opens or closes a circuit by coming in contact with orseparating from the main conductor.

contactor A device that uses a small control current to energize or de-energize a load.

control transformer A type of transformer used to decrease the voltage to the value required by the motor control system.

diaphragm-operated switch A type of pressure switch that senses small pressure changes at low pressures.

direct current Current that flows in one direction. Direct current does not reverse the direction of flow.

electric motor A machine that converts electricity into mechanical energy or motion. An electric motor is a common power source for amechanical system.

electromagnetic starter A device that has a magnetic coil that sends enough voltage to start a motor.

float switch A type of switch that controls the action of a pump as it relates to the level of liquid in a tank. The float switch symbol has acircle connected to a line that represents a ball float.

flow switch A type of switch that detects the movement of air or liquid in a duct or pipe. The flow switch symbol has a flag or paddleshape that represents either an air flow switch or a liquid flow switch.

fuse A safety device that detects excess current in a circuit. Fuses often have a component that melts and opens the circuit.

ladder diagram Another name for a line diagram, due to its resemblance to a ladder. In this sense, each circuit line is a "rung" of the ladder.

limit switch A type of switch that detects the presence or absence of an object. The limit switch symbol has a wedge that represents thebumper arm.

line diagram A diagram that shows the logic of an electrical circuit or system using standard symbols. Also known as a ladder diagram.



Class Vocabulary

liquid flow switch A type of flow switch that detects the movement of liquid. The liquid flow switch symbol has a flag shape that represents apaddle.

logic The reasoning behind the functioning of something. Circuit logic comprises all the principles required to understand electricalcircuitry.

magnetic relay A type of overload relay that senses the strength of the magnetic field that the current flow produces. Magnetic relays areoften used in areas that experience extreme changes in temperature.

maintained contact device A type of device in which the switch or button physically keeps the circuit in the actuated position. An example of amaintained contact device is a light switch.

momentary contact device A type of device in which the switch or button closes or opens the circuit only when it is actuated.

mushroom head A type of pushbutton that is shaped like a mushroom.

National Electrical Manufacturers Association An organization that defines a product, process, or procedure with reference to safety, performance, and testing. NEMAprovides commonly used electrical symbol standards.

normally closed contact An electrical contact that regularly allows electricity to flow. An NC contact has parallel lines with a diagonal line crossingthem showing a closed connection.

normally closed held open A type of switch that is connected normally closed but the contacts are held open when the circuit is de-energized.

normally open contact An electrical contact that rarely allows electricity to flow. An NO contact symbol has parallel lines showing an openconnection.

normally open held closed A type of switch that is connected normally open but the contacts are held closed when the circuit is de-energized.

off-delay timer A type of timer in which the contacts change position immediately when the coil is energized, but delay returning to theirnormal position when the coil is de-energized.

on-delay timer A type of timer in which the contacts delay changing position when the coil is energized, but change back to their normal

position immediately when the coil is de-energized.

output device A device that performs a mechanical action after receiving the electrical signal to do so.

overload relay A device that protects a motor from overheating due to an overload condition in the machinery.

pictorial diagram A type of electrical print that shows the external appearance of each component in the circuit. A pictorial diagram is muchlike a photograph of the circuit.

pilot light A type of indicator light found on machines.

pole A set of moveable contacts that belong to a single circuit.

pressure switch A type of switch that senses the pressure in a pneumatic or hydraulic system. The pressure switch symbol has a semi-circleconnected to a line that represents the diaphragm.

prime mover The device in a power transmission system that introduces energy into the system and converts the energy into theappropriate form.

pushbutton A manual control device that opens or closes a circuit when pressed. Pushbuttons can be normally open or normally closed.

relay An electrically controlled mechanical device that controls one circuit by opening and closing the contacts in another circuit.

schematic diagram An electrical print in which all electrical components are represented with a symbol. Schematic diagrams show the electrical

relationship of all components, but not the physical relationship of the components.

selector switch A type of switch that can be turned to different positions to make a connection with the contacts in that particular position.

series motor A method of connecting field windings in series with the armature. A DC series motor provides very high start-up torque butmust never be run without a load.

shunt field A winding of small wire and many turns designed to be connected in parallel with the armature of a DC motor or generator.

shunt motor A method of connecting field windings in parallel with the armature. The shunt DC motor is commonly used because of itsexcellent speed regulation.

sine wave The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines.

single-phase motor A type of AC motor that operates on either 120 or 240 volts and is used for most simple residential applications like furnaces,washing machines, and air conditioners.

solenoid A coil of wire that converts electrical energy into linear motion.

squirrel cage rotor A type of three-phase AC motor whose rotor is constructed by connecting metal bars together at each end. It is the mostcommon AC motor type.

switch A device that opens and closes a circuit.

symbol Something that is used to signify something else. A schematic symbol represents an electrical component in a diagram.

temperature switch A type of switch that detects the expansion of a metal. The temperature switch symbol represents a bimetal strip.

thermal relay A type of overload relay that connects a heater with a motor.

three-phase motor A motor with a continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all largeAC motors and is the standard power supply that enters homes and factories.

throw The number of stationary contacts that match the moveable contacts.

timing relay A type of relay that delays changing position when the coil is energized or de-energized.

torque A force that produces rotation.

wiring diagram The most detailed of electrical prints. A wiring diagram shows the physical relationship of all the components, as well as theinformation needed to wire the circuit.



Class Vocabulary

wobble stick A type of lever used to actuate contacts on a pushbutton or switch unit.

wound rotor A three-phase motor containing a rotor with windings and slip rings. This motor type permits control of rotor current byconnecting external resistance in series with the rotor windings.

action The third step of a control circuit. Actions are the physical work performed as loads are energized.

AND A type of circuit logic where both normally open control devices must be closed to energize the load. Control devices areconnected in series in AND logic.

automatic signal A type of signal that is sent when an input device detects a change in conditions such as flow, pressure, or temperature.

auxiliary contact An additional motor starter contact used to provide memory to control circuits. When energized, the motor starter closes theauxiliary contact, maintaining a closed circuit.

control device Any input device that controls the flow of current in a circuit. Control devices determine when loads are energized or de-energized.

counter A device that keeps track of the number of entering inputs and provides an output when a preset count is reached. Countersalso usually display the counted value.

cross-reference number The numbers on the right side of a line diagram that reference contacts in other circuit lines that electrically connect theload in the referenced line. Numbers that cross-reference normally closed contacts are underlined.

dashed line method A method of cross-referencing mechanically connected contacts that operate together but on different lines of the diagram.The dashed line method is used on simple diagrams when the contacts are close together.

decision The second step of a control circuit. Decisions are based on the signals received and the logical functions designed in thecircuit.

digital multimeter A device that can measure voltage, current, or resistance. A multimeter is the most versatile and common meter used today.

dual palm buttons Two separate buttons that must be pressed simultaneously in order to power stamping presses. This is an example of AND

logic.

hard-wired Having physical connections that are designed to act the same way over and over.

ladder diagram Another name for a line diagram, due to its resemblance to a ladder. In this sense, each circuit line is a "rung" of the ladder.

limit switch A mechanical input that requires physical contact of the object with the switch actuator.

line diagram A diagram that shows the logic of an electrical circuit or system using standard symbols. Also known as a ladder diagrambecause the diagram appears as individual lines or "rungs" connected between two vertical lines.

line number The sequential numbers running down the left side of a line diagram. Each line, or rung, of the line diagram has its ownnumber.

load Any device that converts electrical energy to motion, heat, light, or sound. A motor starter coil and a pilot light are bothexamples of loads.

logic function The sequence of operations performed by a circuit. Logic functions such as AND and OR follow a set, predictable pattern.

manual signal A type of signal that you send to a circuit through physical action. Flipping a light switch or pressing a pushbutton are manualsignals.

mechanical signal A type of signal that is sent through the mechanical motion of a machine. A gear contacting a limit switch is an example of amechanical signal.

memory The ability of a circuit to store a charge and keep the load energized even after the signal is removed.

momentary contact A contact that returns to its original position immediately after sending a signal.

motor starter An electrically operated switch that uses magnetic induction to provide the startup current for a motor.

NAND A type of circuit logic where both normally closed control devices must be opened to de-energize the load. Control devicesare connected in parallel in NAND logic.

NOR A type of circuit logic where only one normally closed control device must be opened to de-energize the load. Control devicesare connected in series in NOR logic.

normally closed An electrical contact that regularly allows electricity to flow.

normally closed contact An electrical contact that regularly allows electricity to flow until it is signaled to open.

normally open An electrical contact that rarely allows electricity to flow.

NOT A type of circuit logic that uses normally closed contacts.

numerical cross-reference method A method of cross-referencing mechanically connected contacts that operate together but on different lines of the diagram.The numerical cross-reference method is used on complex diagrams when the connected contacts are several lines apart.

OR A type of circuit logic where only one normally open control device must be closed to energize the load. Control devices areconnected in parallel in OR logic.

overload contact A normally closed contact placed in series between a load and the neutral line of a circuit. Overload contacts open only whenan overload condition is present.


relay A device that controls one electrical circuit by opening and closing contacts in another circuit.

signal The first step of a control circuit. Signals are inputs that change the condition of a circuit.

specification A description of the essential physical and technical properties of a machine. Specs are the principle indicator of machinecapability.

switch A control device that can make or break a circuit by closing or opening. A switch can be either manual, mechanical, orautomatic.



Class Vocabulary

terminal number A number assigned by a manufacturer to a device's contact points. Terminal numbers help identify the connection points in acircuit.

tie-down method Connecting one probe of a DMM to the neutral side of a circuit and moving the other probe systematically along the sectionsof a circuit to find the malfunctioning part.

timer A device that delays the signal sent by a control device to a load for a preset amount of time.

troubleshooting The systematic elimination of the various parts of a system, circuit, or process to locate a malfunctioning part.

wire number A reference point on a line diagram used to keep track of the different wires that connect the components in the circuit. Wirenumbers are circled and start with 1 from the top left of the diagram.

armature The part of a motor in which a current is induced by a magnetic field. The armature consists of a series of coils mounted on a shaft androtates through the magnetic field.

base speed The speed (in rpm) at which the motor runs with full-line voltage applied to the armature and the field.

brushes Sliding electrical contacts used to provide a connection between the armature and the external circuit. The brushes are stationary andare contacted by the rotating commutator.

chattering The occasional unwanted vibration between components. Chatter decreases productivity and can cause wear.

commutator The rotating switch that contacts the brushes of a DC motor. The commutator maintains DC when the rotation of the armature switchesthe polarity of the conductor.

compound motor A DC motor that uses both series and shunt field windings. Compound motors provide most of the positives of both types.

constant speed A type of motor that maintains a steady rate of rpm from no load to full load. DC shunt motors are often referred to as constant speedbecause they run at constant speed.

counter emf The voltage induced in the armature of a DC motor that opposes the applied voltage and limits armature current.

DMM A device that can measure voltage, current, or resistance. A digital multimeter is the most versatile and common meter used today forelectrical maintenance.

electric motor A machine that converts electrical energy into mechanical motion. Electric motors use magnetic induction to produce torque.

field windings The conducting wire connected to the armature that energize the pole pieces. Field windings are connected in series or parallel.

frogleg wound armature Term used to describe a series-parallel combination armature winding. Froglegs are the most commonly used winding.

grounded circuit A circuit where current strays from its intended path and flows through the frame of the motor. Grounded circuits are caused whenconductor insultation breaks down or is damaged.

horsepower A unit of power used to describe machine strength. One horsepower equals 33,000 ft-lbs of work per minute, or 746 watts.

inrush current The initial surge of current into the windings. Inrush current can be up to ten times higher than the continuously needed currentbecause there is low initial resistance.

lap wound armature Term used to describe a parallel armature winding. Lap connections are used for high current, low voltage loads.

lockout/tagout A method of protecting employees from accidental machine startup through proper locking and labeling of machines that areundergoing maintenance.

lubricate To use a fluid to reduce the friction between components. Typically a lubricant reduces resistance, heat, and wear, but brushes cannotbe lubricated.

magnetic induction The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines offlux.

permanent magnet motor A type of motor that uses permanent magnets instead of field windings as a way to create torque. A permanent magnet is one thatretains its magnetism after the magnetizing force has been removed.

polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow.

pole piece Devices mounted on the inside of a motor housing. When connected to field windings, the pole pieces form the electromagnets thatcreate lines of flux.

rheostat A continuously variable electrical resistor used to regulate current.

right-hand motor rule The relationship between the factors involved in determining the movement of a conductor in a magnetic field. The current flow isopposite in generators.

self-excited shunt field Field windings connected in parallel with the armature that are supplied with current by the same power supply as the armature.

separately excited shunt field Field windings connected in parallel with the armature that are supplied with current from a source other than the armature. Aseparately excited field helps maintain constant speed.

series motor A method of connecting field windings in series with the armature. A DC series motor provides very high start-up torque but must neverbe run without a load.

series-parallel A compound connection that uses both series and parallel connections.

short circuit A circuit where current takes a shorter, unintended path between two conductors. Short circuits are caused when the insultation of twoconductors is worn or damaged.

shunt motor A method of connecting field windings in parallel with the armature. The shunt DC motor is commonly used because of its excellentspeed regulation.

speed The amount of distance an object travels in a given period of time. In motors, speed reflects rotational movement and is measured inrevolutions per minute.

speed control The external means of varying the speed of a motor under any type of load.

speed regulation The ability of a motor to maintain its speed when a load is applied. A motor's speed regulation is fixed based on its design.



torque A force that produces rotation. Torque is measured in pounds-feet in the English system and Newton meters in the metric system.

wave wound armature Term used to describe a series armature winding. Wave windings are used for high voltage, low current loads.

Solenoid

air gap A small space left between the solenoid core and the armature to break up the magnetic field. Without an air gap, the armature could remainstuck in the closed position even when the solenoid is de-energized.

armature The moveable part of a solenoid that performs work.

bell-crank solenoid A type of solenoid that uses a lever attached to the armature to soften the impact of the linear force.

chattering The occasional unwanted vibration between components. Chatter decreases productivity and can cause wear.

clapper solenoid A type of solenoid that hinges the armature on a pivot point to produce a more gradual force.

coil Multiple loops of conducting wire used to create a magnetic field when current is passed through it.

cycle One complete motion of a solenoid from its resting position to full extension and back.

DMM A device that can measure voltage, current, or resistance. A digital multimeter is the most versatile and common meter used today for electricalmaintenance.

duty cycle A rating of solenoid life expectancy based on the number of operations per minute.

eddy current loss A phenomenon caused by the rate of change in an induced magnetic field. The relative motion causes a circulating flow of electrons or currentwithin the conductor, leading to efficiency loss.

efficiency loss Natural effects that cause energy output to be less than energy input. While efficiency losses can be minimized with good design, no system is100% efficient.

generator A device that converts mechanical energy into electrical energy by magnetic induction.horizontal action A type of simple solenoid in which the armature makes a direct side-to-side movement.

hydraulic system A power transmission system that uses the force of flowing liquids to transmit power.

inductive reactance The magnetic opposition to current flow in a coil. During inductive reactance, changes in a magnetic field produce a voltage that is counter to thenormal direction of current flow.

inrush current The initial surge of current into a solenoid. Inrush current can be up to ten times higher than the continuously needed current because there islow initial resistance.

left-hand flux rule A method used to determine the relationship of the motion of the conductor in a magnetic field to the direction of the induced current. Fluxrotates around the conductor as shown by the left hand.

linear motion Motion that takes place in a straight line rather than rotating in place around an axis.

magnetic flux A measure of the strength of the field formed around a magnet. Flux is expressed in webers (Wb).

magnetic induction The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.

plunger solenoid A type of solenoid that uses a spring-loaded iron rod. The rod tries to align with the magnetized coil when energized, creating linear motion.

pneumatic system A power transmission system that uses the force of flowing gases to transmit power.

polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow.

position The number of physical settings on a directional control valve. A three-position valve can be placed in three different physical settings with acontrol such as a lever.

solenoid An output device that converts electrical energy into linear mechanical force.

specifications A description of the essential physical and technical properties of a machine or device. Specifications or "specs" often include voltage and strokeratings.

tolerance The acceptable variation from a specified dimension.

transient A short surge of current or voltage, often occurring before steady-state conditions have become established.

valve A mechanical device by which the flow of liquid, gas, or other objects may be regulated by moveable parts that open, close, or obstruct one ormore openings or passageways.

vertical action A type of simple solenoid in which the armature makes a direct up and down movement.

Ac motor

AC motor A type of electric motor that runs on alternating current. AC motors are more commonly used in industry than DC motors but do notoperate well at low speeds.

alternating current Current that regularly reverses the direction of its flow in a repeating, cyclical pattern.

armature The part of a motor or generator in which a current is induced by a magnetic field. The armature usually consists of a series of coils orgroups of insulated conductors surrounding a core of iron.

bearing A friction-reducing device that allows one moving part to glide past or rotate within another moving part.

brush A device found inside a generator that is used only in pairs to transfer power from a rotating object. Brushes rest on the commutator ofa DC motor.

capacitor An electrical device that stores energy and releases it when needed. A capacitor gives a single-phase motor more torque but has alimited life.



Contactors and starters

AC magnetic motor starter A type of starter for AC induction motors that combines a magnetic contactor and an overload relay. Magnetic motor starters canbe operated remotely.

across-the-line starter A category of starters in which the motor is directly connected to the supply lines, allowing full voltage when the motor starts.

amperage A measurement that indicates the amount of current flowing in a circuit. Amperage is measured in amperes.

arc chute A method of arc suppression that extinguishes arcs by channeling them into chambers above the contacts.

arc column A string-like spark of electricity that connects across the gap between two contacts. Arc columns occur when electricity flows viaionized air molecules or vaporized metal and results in damage to the contacts.

arc suppression Any method used for extinguishing electrical arcs between contacts. Arc suppression is necessary to ensure worker safety andprolong contact life.

arcing The flow of electricity through the air from one conductor to another. Arcing can produce visible flashes and flames.

armature The part of a motor in which a current is induced by a magnetic field. The armature usually consists of a series of coils or groups ofinsulated conductors surrounding a core of iron.

auto-transformer A type of reduced voltage motor starter that uses a single-coil transformer to step voltage up or down.

bimetallic strip A strip made by bonding together two unlike metals that expand at different rates when heated. The different rates of expansioncause the bimetallic strip to curl.

bimetallic thermal overload relay A type of thermal overload mechanism that uses a strip composed of two different metals. When heated, the two metals expand atdifferent rates, causing the strip to warp and create an opening in the circuit.

blowout coil A method of arc suppression that uses magnetic coils to create a magnetic field that pushes an arc upward until it breaks.

break The term for the number of places in which a circuit can be made or broken.

circuit breaker A safety device that detects overcurrent in a circuit. A circuit breaker often contains a bimetallic strip that bends and trips aswitch that opens a circuit.

closed contact A point where two contacts connect with each other and allow current to flow, creating a circuit.

contact A conductive metal part in an electrical circuit that opens or closes the circuit by either separating from or touching a matchingpart.

contact bounce An unwanted effect that occurs when contacts close via high amounts of pressure and then rebound from each other due to theforce. Contact bounce is undesirable because it can create secondary arcs and reduce contact life.

contact life The length of time the surface of a contact will remain in good working condition.

contactor A device that uses a small control current to energize or de-energize a load. Contactors can handle high amounts of current andare also combined with overload relays to create motor starters.

control component Any device that controls circuits, motors, and other electric or mechanical devices.

control relay An electrical switch that opens and closes a circuit. Relays can open or close one or many sets of contacts.

dashpot oil Oil that maintains viscosity over a wide range of temperatures. Dashpot oil is used in dashpot overload relays.

dashpot overload relay A type of overload relay in which a piston moves within a cylinder containing dashpot oil that is used to dampen and controlmotion.

de-ionizing Removing ions from a fluid or air and consequently prohibiting electrical conductivity. Ions are atoms that are electrically chargeddue to the loss or gain of one or more electrons.

delta A connection of three components where a triangular series circuit is formed. Delta connections are used in wye delta reducedvoltage starters.

double-pole double-throw A set of 2 moveable contacts that can break a circuit in 2 places each.

double-pole single-throw A set of 2 moveable contacts that can break a circuit in 1 place each.

electronic overload relay A type of overload relay with a heaterless design that detects overload by monitoring motor current.

electronic reduced voltage starter A type of reduced voltage motor starter that is electronically controlled with no moving parts. Electronic reduced voltage starters

regulate voltage to the motor in a series of small bursts of power until the motor reaches full power.

eutectic overload A type of thermal overload relay that uses a melting alloy to activate mechanical devices to open a circuit in the case of overload.

fuse A safety device that detects excess current in a circuit. Fuses often have a component that melts and opens the circuit.

heat sensitivity The ability of a device to detect heat.

IEC The International Electrotechnical Commission, which governs electrical equipment standards in Europe and all other internationalcountries.

induction motor A commonly used industrial motor in which power is connected only to the stator. Alternating current in the stator induces currentin the rotor and creates an electromagnetic field that produces rotation in the armature.

inrush current The initial surge of a current into a motor. Inrush current can be 12 times higher than current required for normal motor operation.

ionized Exhibiting a negative or positive charge after gaining or losing one or more electrons.



knife blade switch A lever-type switch that is used to control contactors.

magnetic contactor A type of contactor that is operated remotely through solenoid action.

magnetic overload relay A type of overload relay that is operated remotely through solenoid action.

magnetic relay A type of overload relay that senses the strength of the magnetic field that the current flow produces. Magnetic relays are oftenused in areas that experience extreme changes in temperature.

manual contactor A type of contactor that is operated by a person who activates a switch on the contactor.

manual controller An input device that requires a manual switch to control the flow of current in a circuit.

manual starter A type of starter that is operated by a person who activates a switch on the starter.

melting alloy overload relay A type of thermal overload relay that uses a melting alloy to activate mechanical devices to open a circuit in the case of overload.

motor overload protection The use of devices such as overload relays to open the circuit in the event of an overload to prevent the motor from overheating.


movable contact A contact on an armature that moves and connects to a matching stationary contact.

NEMA The National Electrical Manufacturers Association, which sets standards for equipment used in the United States.

normally closed Contacts that keep the circuit connected during normal operation and disconnect to open the circuit when the relay is activated.

open contact A contact that is separated with space between another matching contact, allowing no current to flow.

output device A device that performs a mechanical action after receiving the electrical signal to do so.

overcurrent Excess current. Devices like fuses and circuit breakers protect against overcurrent.

overload Excessive heating due to motor overcurrent and failure of motor to start.

overload relay A relay that is attached to a contactor in order to create a motor starter. Overload relays protect the motor from overload bydisconnecting the power to the motor and stopping its operation.

part-winding starter A type of reduced voltage starter that applies power to only one set of windings, then to the other set as the motor comes up tospeed.

pawl A hinged or pivoted device that fits into the notch of a ratchet, wheel, gear, or bar. A ratchet and pawl work together, either toproduce forward motion or to prevent backward motion.

piston A rod inside a cylinder that is moved by hydraulic pressure.

pole The term for a set of moveable contacts that belong to a single circuit.

power relay A relay with heavy-duty contacts that is usually rated 15 amperes or higher. Power relays are also known as contactors.

primary resistor A type of reduced voltage starter that uses resistors to create an initial 30% drop in voltage before allowing full current to themotor.

ratchet wheel A toothed wheel that uses a bar called a pawl to keep it from turning in one direction.

reduced voltage starter A category of motor starters that reduce the power coming into the motor when it is initially started.

relay An electrical switch that opens and closes a circuit. Relays can open or close one or many sets of contacts.

resistor Am electronic component that regulates, limits, or opposes the flow of electrical current. Resistors tend to convert electricalenergy into heat.

secondary arc An arc caused by contact bounce. The first arc is extinguished when contacts close, then a second arc is created when contactsbounce open again.

shaft A long cylindrical device such as a rod or pole.

silicon chip A miniature electronic circuit also known as an integrated circuit or microchip.

solder pot overload A type of thermal overload relay that uses a melting alloy to activate mechanical devices to open a circuit in the case of overload.

solenoid principle The use of a coil that enables voltage to convert electrical energy to mechanical energy via magnetic fields.

solid state Any device or system that functions by means of electronic components without the use of moving parts.

squirrel cage A type of three phase AC rotor that is constructed by connecting metal bars together at each end. It is the most common AC rotortype.

stationary contact A contact that remains in a fixed position during operation.

switch A control device that can make or break a circuit by closing or opening. A switch can be either manual, mechanical, or automatic.

tap An intermediate connection point on an electrical transformer.

thermal relay A type of overload relay that connects a heater with a motor. A thermal relay protects a motor by shutting it down if the relaydetects excessive heat.

throw The term for the number of contacts that match the moveable contacts.

tip bar A mechanical part in a magnetic overload relay that tilts during overload and releases the support to a set of closed contacts,causing them to open and break the circuit.

trip time The time it takes for a device to open a circuit in the event of an overload.

viscosity A fluid's resistance to flow. Viscosity is used to describe friction of fluids.

warp To bend something that was formerly straight.

winding An electrically continuous length of insulated wire wound on a bobbin, spool, or form.

wye delta The configuration of motor windings in which windings form the shape of the letter Y, then a triangle shape called a delta.



Reversing motor circuits

armature windings The coiled, insulated conductors surrounding the armature through which current is run to create a magnetic field. Reversing thecurrent flow through the armature windings in DC motors reverses motor rotation.

auxiliary contact interlock A backup system used in magnetic motor starters to provide electrical isolation. Also called electrical interlock.

brake To slow and eventually stop motion. Reversing current flow in a motor can be used as a frictionless method of braking.

contactor A device that uses a small control current to energize or de-energize a load. Contactors can handle high amounts of current and arealso combined with overload relays to create motor starters.

control circuit A type of circuit that uses control devices to determine when loads are energized or de-energized by controlling current flow. Controlcircuits usually carry lower voltages than power circuits.


control transformer A electromagnetic device that steps down voltage to levels useable by loads in a control circuit. Control transformers also provideelectrical isolation.

drum switch A switch used to manually reverse a motor circuit. A drum switch mounts moving contacts on a rotating shaft.

electrical interlock The type of electrical isolation provided by auxiliary contacts in magnetic motor starters.

field windings The conducting wire connected to the armature that energize the pole pieces. Field windings are connected in series or parallel.


limit switches A type of switch that detects the presence or absence of an object by physically touching it. Limit switches have a variety of actuatorsthat come into contact with an object.

magnetic starter A magnetic switch with overload protection that uses a solenoid to open and close contacts to a motor circuit.

manual reversing starter A device that combines two manual motor starters to add forward and reverse pushbuttons to the regular start and stop buttons.Reversing starters need only one overload device and must provide mechanical interlock.

manual starter A manual switch with overload protection used to provide control to a motor.

mechanical interlock Arranging forward and reverse contacts so that it is physically impossible for both sets of contacts to close at the same time.

motor control circuit A circuit designed to provide power and control to electric motors.


NEMA National Electrical Manufacturers Association. NEMA provides ratings for various types of motor designs.

overload relay A relay that is attached to a contactor in order to create a motor starter. Overload relays protect the motor from overload bydisconnecting the power to the motor and stopping its operation.

power circuit A type of circuit that carries power to electrical loads. Power circuits often carry high voltages and consist of incoming main power, amotor starter, and the motor.

programmable logic controller A processor driven device that uses logic based software to provide electrical control to machines.

running winding The primary stator winding of a single-phase AC motor. Running windings are constructed from heavy, insulated copper wire.

solenoid principle Using a coil that utilizes voltage to convert electrical energy to mechanical energy via magnetic fields.

starting winding The auxiliary stator winding of a single-phase AC motor. Starting windings are constructed from fine, insulated copper wire.

Distribution system

branch circuit The part of a distribution system consisting of circuit conductors, between the final overcurrent protection and the outlet or loadattached.

busbar Thick, rigid strips or bars of copper that serve as a common connection between several circuits. Busbars are usually used near theswitchboard and can be enclosed in busways.

busway The part of a distribution system consisting of metal enclosed busbars. Busways come in premade sections that can be fitted to anyshape needed.

center tap The point where all three windings are connected to each other in a wye connection. For delta connections, one of the lines must betapped to produce a neutral.

copper loss A power loss due to current flowing through wire. Copper loss is proportional to the resistance of the wire and the square of thecurrent.

core A component of a transformer. The iron or steel core provides a controlled path for the magnetic flux generated in the transformer bythe current flowing through the windings.

delta A connection of three components where a triangular series circuit is formed. Delta connections are used in three phase power



systems.

delta/delta A transformer with both the primary and the secondary connected as a delta.

delta/wye A transformer with the primary connected as a delta and the secondary connected as a wye.

distribution substation A bank of step-down transformers near the end users. The distribution substation converts voltage closer to the required usablelevels.

distribution system A circuit of users linked to a generating station and substations that is typically arranged in either a radial or interconnected manner.Local distribution systems transport power within a building.

enclosure A physical barrier designed to provide mechanical or electrical protection for components used in a system.

feeder A circuit conductor between the power supply source and a final branch circuit overcurrent device.

generating station A building where a utility company houses large linked AC generators to create the massive power for widespread use.

grounded conductor A system conductor that is intentionally grounded.

grounding conductor A conductor used to connect equipment in a wiring system to ground.

interconnected system A distribution system with multiple available power sources that can loop throughout the network. If one source goes down, adifferent source can be activated to maintain service.

kilovolt-amp A unit used to rate transformer and generator strength. A kilovolt is a thousand volts.

laminated Sealed together in multiple layers of thin sheets to construct the core for a transformer. Lamination helps reduce resistance losses.

line voltage The voltage present between any two of the conductors in a three-phase system. It is 1.732 times higher than phase voltage in a wyeconnection.

load center A device found in residential locations that performs the same functions as a panelboard does in commercial settings. Load centersare not required to have many panelboard safety features because homes do not draw the same amount of current as industry.

local power distribution system The part of a distribution system located within a building. Local distribution systems are the responsibility of shop electricians and

maintenance workers and fall under NEC rules.

main disconnect switch A heavy, spring-loaded switch on a factory switchboard that can cut off power to the entire building. Switchboards with more than sixswitches or breakers are required by the NEC to have a main disconnect.

motor control center A modular assembly specifically designed to plug in motor control units. Motor control centers are supplied by a common bus, usuallystraight from the switchboard.

mutual induction The ability of one coil to induce a voltage into another coil. This principle is used in transformers to step up or step down voltage.

NEC The standard for minimum safe electrical installations. The National Electrical Code is adopted in some form as law in all 50 states.

network system A distribution system where multiple power sources are connected to each user to guarantee uninterrupted power. A network systemis expensive, so it is used only when constant power is vital.

open delta A transformer connection that does not complete the triangle, using only two of the three sides. An open delta is used when fullpower is not needed.

overcurrent Excess current that may result from overload, short circuit, or ground fault. Devices like fuses and circuit breakers protect againstovercurrent.

panelboard A single panel distribution cabinet or wall cutout box that holds automatic overcurrent protection devices for lighting, heat, or powercircuits.

phase symbol () The Greek letter Phi, used to represent phases, such as in a 34W system.

phase voltage The voltage between any one conductor and ground.

plug-in busway A type of feeder busway with electrical control that allows loads to be added along the bus structure.

primary winding Turns of wire on a transformer core, used to transfer voltage from the input to the core.

radial system A distribution system with only one power source. If that source goes out, power is lost to the entire circuit.

revolving field generator A generator setup where an electromagnetic field is rotated between the conductor wound armature. Most AC generators are of thisdesign.

secondary winding Turns of wire on a transformer core, used to transfer voltage from the core to the outside load.

service-entrance The point where electricity enters a buidling. A service-entrance switchboard has metering equipment and devices for overcurrentprotection and electrical control.

single-phase A continuous single alternating current cycle.

step up In electricity, a phrase used to describe voltage adjustment. To step up voltage means to increase voltage.

substation Any grouping of switchgear and transformers located near a source or user. Substations are used to alter voltage levels and provide aservice point of electrical control.

switchboard A freestanding assembly of panels with metering equipment, overcurrent and other protection devices. Switchboards take a largeblock of power from a substation and break it down into smaller blocks for use within a building.

switchgear A combination of disconnect switches and breakers used to isolate equipment in substations.

tap A wire connected to the midpoint of a transformer secondary winding. This allows the transformer to use different turns ratios.

terminal A connecting point in a circuit where a wire is attached to create an electrical connection.

three-phase A continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large scale distributionsystems.

three-phase power The most common form of AC power for distribution. Three-phase power has three overlapping AC cycles offset by 120 degrees.

transformer A device that transfers electrical energy from one circuit to another, without changing the frequency, using electromagneticinduction. A transformer is most often used to change the line voltage.



transmission substation A bank of step up transformers near the generating station. Transmission substations increase voltage as high as 800kV for widespreaddistribution.

turns ratio A comparison of the number of turns in the primary versus the number of turns in the secondary of a transformer.

wye A connection of three components where one end of each component is connected at a common point. Wye connections are used inthree phase power systems.

wye/delta A transformer with the primary connected as a wye and the secondary connected as a delta.

wye/wye A transformer with both the primary and the secondary connected as a wye.

Servo motor

AC motor A type of electric motor that runs on alternating current. AC motors are more commonly used in industry than DC motors, but do notoperate well at low speeds.

AC servomotor A servomotor based on the design of conventional AC motors, with the addition of an amplifier and a feedback device.

AC synchronous servomotor A servomotor based on the design of conventional AC synchronous motors, with the addition of an amplifier and a feedback device.

algorithm A mathematical process designed to systematically solve a problem. A complex algorithm is used to control and stablize the outputs in aclosed-loop control system.

amplifier A device that increases the size or strength of a signal. Servomotors use amplifiers as part of the motor control system.

analog servo A servo that outputs a continuously variable signal. Analog signals differ from digital signals in that small fluctuations in the analog signalare meaningful.

armature The part of a motor in which a current is induced by a magnetic field. The armature consists of a series of coils mounted on a shaft androtates through the magnetic field.

automatic feedback Feedback that is controlled by an electronic or electromechanical mechanism rather than a person. Automatic feedback is used in closed-loop control systems.

back-driving A condition that occurs in stepper motors in which there is an unwanted reversal of the motor shaft, resulting in step loss.

brushes Sliding electrical contacts used to provide a connection between the armature and the external circuit. The brushes are stationary andare contacted by the rotating commutator.

brushless DC motor A DC motor that uses a permanent magnet instead of brushes to run the motor.

brushless DC servomotor A servomotor based on the design of a conventional brushless DC motor, with the addition of an amplifier and a feedback device.

closed-loop control A type of control system that automatically changes the output based on the difference between the feedback signal to the input signal.Servomotors can be used on closed-loop control systems.

commutator The rotating switch that contacts the brushes of a DC motor. The commutator maintains DC when the rotation of the armature switchesthe polarity of the conductor.

continuous current The maximum amount of current that can be applied without overheating the motor. Continuous current is one of the specifications usedfor sizing AC servomotors.

continuous power output The ability of a motor to output its full power for a sustained period of time. Continuous power output is one of the specifications usedfor sizing AC servomotors.

continuous torque The amount of torque that can be provided by the motor under normal running conditions. Continuous torque is one of the specificationsused for sizing AC servomotors.

control system A manual or automatic mechanism used to manage dynamic processes by adjusting or maintaining physical variables such as temperature,speed, or flow rate.

count An increment on an encoder that measures the distance a robotic arm has traveled.

cycle A single increment of something that occurs repeatedly. AC flows in cycles of 360 electrical degrees.

DC motor A type of motor that runs on direct current. DC motors have better speed control and higher torque than AC motors.

DC servomotor A servomotor based on the design of a conventional DC motor, with the addition of an amplifier and a feedback device.

digital servo A servo that outputs a series of pulses or signals that represent "on" or "off," often resulting in binary strings of 0s and 1s.

electrical degree A unit of measurement for expressing the amount of rotation in a generator and the position in an AC sine wave.

encoder A measuring device for motion control that is divided into a fixed number of increments called counts. As the encoder disk spins, lightpulses from an LED are converted to electrical pulses.

feedback signal The actual value detected by a sensor as a process is taking place. The feedback signal is part of a closed-loop control system.

frequency A measurement of the number of complete AC cycles that occur in one second. Frequency is measured in Hertz (Hz).

holding torque The amount of torque required for a motor to remain in a fixed position.

induction motor A type of AC motor that uses electrical current to induce rotation in the coils.

LED Light emitting diode. A semiconductor device that emits a narrow spectrum of light in a forward direction.

microprocessor A tiny central processing unit. Digital servos use a microprocessor to process input signals.



open-loop system A type of control system that uses only an input signal to actuate an output. There is no automatic feedback to adjust the process, soadjustments must be made manually by the operator.

output shaft The part of a motor that transmits torque.

overshoot To exceed a set value.

peak negative voltage The lowest negative point on a wave. The peak negative voltage indicates the maximum negative voltage of the wave.

peak positive voltage The highest positive point on a wave. The peak positive voltage indicates the maximum positive voltage of the wave.

pick and place An application in which objects are transferred from one place to another.

position control A type of control system designed for moving objects or machines to a known position. Servomotors are used for position control.

resolver An analog motor control device that controls feedback through a sine wave. The level of voltage on the sine wave correlates to theposition of the rotor within one revolution.

rotor The rotating part of a motor.

service factor A rating given to motors to indicate what applications they can be used for.

servo drive A motor control device that outputs electrical signals to a servomotor to induce motion. The servo drive can be built in as part of themotor or it can be a separate device.

servo system A closed-loop control system that utilizes a servomotor.

servomotor A type of motor used in applications that require precise positioning. Servomotors provide a high amount of holding torque to maintaintheir position accurately.

shaft speed The rate at which the motor shaft turns. Shaft speed is measured in feet per minute (fpm) or in meters per minute (mpm).


single-phase AC voltage that has only one sine wave.

soft start A motor starting method that reduces stress on a motor by allowing it to accelerate gradually for a programmed period of time.

squirrel cage rotor A type of three-phase AC rotor that is constructed by connecting metal bars together at each end. It is the most common AC rotor type.

start-stop test A troubleshooting method in which the stepper motor is connected to a load and a fixed frequency is applied to the driver. Stop-starttests are used to diagnose the causes of step loss.

stator The stationary windings of a motor, usually inside an AC motor.

step loss A phenomenon in which the stepper motor does not take a step after receiving an input pulse.

stepper motor A type of motor that rotates in small, precise increments in response to an electronic pulse. Stepper motors can rotate forward orreverse, but they cannot move large loads.

synchronous motor A constant-speed AC motor that does not use induction to operate. A synchronous motor needs DC excitation to operate.

target value A preset value such as a specific temperature, speed, or flow rate that the control system is supposed to reach. The type of preset valuefor servomotors is position.

three-phase AC voltage that has three sine waves.

tuning A system of adjusting the servomotor's outputs by adjusting values in the algorithm controlling the closed-loop system.

undershoot To fall short of or below a set value.

windings The conducting wire connected to the armature that energize the pole pieces of a motor.

Timers

555 integrated circuit A type of integrated circuit that is often used to regulate the timing functions of electronic timers.

air bellows An apparatus consisting of a flexible, valved air chamber that is contracted and expanded by pumping action to force air through anozzle. Air bellows are used to sound a pipe organ, increase draft to a fire, or operate a pneumatic timer.

analog timer A timer that tracks physical quantities or changes using a varying frequency. Unlike digital signals, analog signals easily handle inputthat is highly variable in quality and quantity.

arithmetic counter A type of counter that performs arithmetic operations such as addition, subtraction, multiplication, and division.

automatic overriding program A program that counteracts the normal operation of a device or process.

axle A rotating shaft attached to a wheel or gear.

batch counter A counter that counts in series a collection of objects or data that is treated as a single entity.

bimetal strip timer A type of thermal timer that uses a strip formed by joining two different metals with different expansion rates into one strip thatbends when the strip is exposed to heat and temperature changes.

cam A circular or cylindrical machine component that converts rotational movement into linear movement.

cam timer A type of mechanical timer that uses cams arranged along a shaft to alternately press down and release switches that control differenttiming elements of a system.

clutch A coupling found inside a motorized device that engages or disengages parts to drive a mechanism.

composite load The collection of devices or systems that consume energy from the timing system·s primary energy source.





control screw A screw that is tightened or loosened to refine the performance of a device.

count range The maximum value the counter can count and register. The count range of the counter is determined by the number of digits thecounter is able to display.

count speed The value indicating how fast a counter can count. Count speed is measured at counts per minute and varies depending on the type ofcounter.

counter A device that counts, calculates, or keeps a record of the number of times something happens.

dashpot timer A category of mechanical action timers that operate by displacing air or viscous fluid. Dashpot timers are the oldest type of industrialtimer, and they are typically used for heavy-duty equipment.

delay timer A timer that delays turning on a device until a preset time period has passed. A delay timer in a car automatically shuts off theheadlights after the car has been turned off.

delayed make An elapsed span of time before two electrodes connect to form a circuit.

dial A flat disk containing numbers or markings around it that rotates to display a specific setting or an output value.

digital Consisting of information that is input or output electronically as a series of pulses or signals either "on" or "off," often resulting inbinary strings of 0s and 1s.

digital timer A timer that operates electronically, providing input or output as a series of pulses in binary strings of 0s and 1s.

DIP switches A Dual In-line Package Switch. DIP switches use binary settings, on-off / yes-no, to configure various options on a device.

down-count Counting in a downward or decreasing direction. Counting 3, 2, 1, and so on is a down-count.

dual-bimetal-strip timer A type of thermal timer that uses two bimetal strips. A bimetal strip joins two different metals with different expansion rates into onestrip that bends when the strip is exposed to heat.

electromechanical counter A category of counters that operate through a combination of electricity and mechanical motion. Electromechanical counters receivean electrical input signal and convert it to mechanical action to output a count, stop a count, or reset the counter to zero.

electromechanical timer A category of timers that operate through a combination of electricity and mechanical motion. Electromechnical timers are graduallybeing replaced by solid state technology.

electronic counter A category of counters that operate through electricity only. Electronic counters execute counting functions through digital signals andcan handle fast counting rates.

electronic timer A category of timers that operate through electricity only and have no moving mechanical parts.

event counter A counter that counts how many times a specified condition occurs.

frequency counter A counter that counts the number of times something happens within a specific time or count limit. In essence, a frequency countercombines the functions of a timer and counter.

gear A circular toothed component that engages, rotates, and transmits power to another circular toothed component when rotated.

gear train A set of gears arranged to transfer mechanical energy from one part of a mechanical system to another.

hydraulic timer A type of timer that creates a time delay by controlling the rate at which liquid passes into or out of a container.

hysteresis The delay between the action and reaction of a measuring instrument. Hysteresis also refers to the tendency of a component's positionto be dependent on the previous position of the component when reacting to a physical stimulus.

idle state The state in which current is flowing, but a device is not energized or in motion.

integrated circuit A miniaturized electrical network used to transmit electric power. A microchip is an example of an integrated circuit.

interval timer A timer that begins the timing period when the control coil is turned on and starts an operational cycle. The control coil remains onand the contacts turn on for a time, then off for a time. This cyclical event is the interval.

LED display A luminous panel on which digital readouts are displayed.

load control element The part of a timing system that controls the load when it receives a signal from the triggering element and switches the load.

manual override A procedure in which an automatic system is put under manual control.

mechanical counter A category of counters not powered by electricity, but by mechanical means such as pushing a button or turning a knob.

mechanical timer A category of timers not powered by electricity, but by mechanical means using air bellows, pistons, or plungers.

mercury A metallic element that is liquid at room temperature. Mercury is used in mercury displacement timers and acts as the contactor inthe device.

mercury displacement timer A timer that operates by displacing a pool of mercury in a container. Mercury displacement timers are used in environments that mayget very hot, or that require the timer to be completely sealed.

motor-driven cycle timer A motor-operated timer that cycles on and off continuously, or goes through one cycle only.

motor-driven delay timer A motor-operated timer that creates a delay after the coil is energized.

motor-driven interval timer A motor-operated timer that begins the timing period when the control coil is turned on and starts an operational cycle. The controlcoil remains on and the contacts turn on for a time, then off for a time. This cyclical event is the interval.

motor-driven reset cycle timer A motor-operated timer that returns to its original starting position after a preset time interval has passed.

motor-driven timer A timer that is operated by a motor. Motor-driven timers are also referred to as cam timers.

multivibrator An electronic circuit used to control signal pulses.

NC Normally closed. An NC electrical contact regularly allows electricity to flow until it is signaled to open.

needle valve orifice The opening to a valve used to provide very fine adjustment. Needle valves require many turns to open them completely.

NO Normally open. An NO electrical contact does not allow electricity to flow until it is signaled to close.

off-delay timer A delay timer that immediately closes contacts when the control coil is energized, then waits for a predetermined amount of time to



open them after power is removed from the coil.

on-delay timer A delay timer that waits for a predetermined amount of time before closing a set of contacts and energizing a load.

operating lifetime The length of time that a device will work before it becomes unreliable or stops functioning.

oscillator An electronic device used to generate a vibrating signal at a constant rate.

PLC Programmable Logic Controller. A processor driven device that uses logic based software to provide electrical control to machines.

pneumatic timer A timer that creates a time delay by controlling the rate at which air passes into or out of an air bellows.

predetermining counter A counter set in advance to stop or produce output once a specific count has been reached. A predetermining counter is also called apreset counter.

preset counter A counter set in advance to stop or produce output once a specific count has been reached. A preset counter is also called apredetermining counter.

pushbutton counter A type of mechanical counter used for manual counting. The operator actuates a pushbutton and records one count for each actuation.

pushbutton switch A manual control device that opens or closes a circuit when pressed. Pushbuttons can be normally open or normally closed.

recycle timer A timer that performs continuously until it is stopped.

relay A device that controls one electrical circuit by opening and closing contacts in another circuit.

repeat cycle timer A timer that performs continuously until it is stopped.

reset timer A type of recycle timer that uses a clutch mechanism to actuate a motor-driven gear assembly and start a cycle.

resolution The smallest value that can be counted. This value can be as small as 1/1000th.

revolution counter A counter that records one count for each revolution of the shaft. Revolution counters are used in odometers to keep track of themiles that tires run by counting axle revolutions.

rotary counter A counter that records a specified number of counts per rotation.

rotary ratchet counter A type of stroke counter. Stroke counters record one count for each stroke.

safety interlock A safety device that disables or prevents a machine startup if a guard or door remains open.

single revolution cycle One turn of a mechanical device.

slow break Allowing for a delay before the connection is broken.

solenoid A type of output device coil that converts electrical energy into mechanical energy via magnetic fields to exert a force, typically in alinear direction. Soleniods can be used to activate switches and valves.

solid state Functioning by means of electronic components without the use of moving parts.

solid state timer A timer that functions by means of electronic components without the use of moving parts.

stroke counter A counter that records one count for each stroke. A stroke is a reciprocating back and forth motion.

thermal expansion timer A timer that operates by heating an upright piece of metal, causing it to expand and close a set of contacts.

thermal timer A type of analog timer that uses heat generated from an electric current to bend a bimetal strip, which closes a set of normally opencontacts. The time it takes to heat the bimetal strip produces the timing delay.

thumbwheel A rotary device that allows an operator to input numerical information into a counter.

timer A control device that automatically starts or stops machines and other devices when a preset time period has been exceeded.

timing element The mechanism in a timing system that produces the time delay.

timing system An electronic system that uses a timer to energize or de-energize a load.

totalizing counter A counter that sums up the total times something has occurred since the last time the counter was used. Most totalizing counters arenon-resettable, and will simply roll over to zero once they have exceeded their count range.

triggering element The part of an electronic timer that detects changes in the timing element and processes the signal for the load control element.Usually this involves amplifying the signal enough to trigger the load control switch.

up-count Counting in an upward or increasing direction. Counting 1, 2, 3, and so on is an up-count.

viscosity A fluid's resistance to flow. Viscosity is used to describe friction of fluid.

Electronic semiconductor device

555 timer A semiconductor device that controls various modes of on/off states in electrical systems. The 555 timer is one of themost widely used types of integrated circuits.

amplification The process of increasing the size or strength of a signal.

amplifier gain The ratio of an output signal's amplitude divided by the input signal's amplitude. Amplifier gain measures the degree towhich a signal has been strengthened.

amplify To increase the size or strength of a signal.

amplitude The maximum height or depth of a sine wave.

AND A logic function where both A and B must be true to trigger C. AND employs a logic that works similar to a series circuit.

anode The positive terminal of an electric current flow.

antimony An element used to dope silicon to create an N-type semiconductor.



astable A mode in which a 555 timer produces a continuous string of on/off pulses at a preset frequency.

avalanche breakdown A process that occurs in a diode when high voltage causes free electrons to travel at high speeds, colliding with otherelectrons and knocking them out of their orbits. The result is a rapidly increasing amount of free electrons.

avalanche diode A specialized diode that acts as a relief valve for excess voltage. Avalanche diodes are sometimes used in combinationwith Zener diodes.

base The input control terminal of a semiconductor device. Also called a gate.

bipolar transistor A three-layer semiconductor device that can conduct current in either direction. Bipolar transistors provide current gainand voltage amplification in a circuit.

bistable A mode in which a 555 timer changes from 1 to 0 or from 0 to 1 when current is applied. The timer will remain in thetransitioned state until it receives a new input.

boron An element used to dope silicon to create a P-type semiconductor.

breakdown A condition that occurs when maximum reverse voltage in a diode is exceeded. Breakdown will cause a diode to fail andpass a large amount of current in the reverse direction.

breakdown voltage A term used to describe the level of AC or DC voltage that results in the failure of a semiconductor device.

capacitance The ability to store an electrical charge.

cathode The negative terminal of an electric current flow.

CMOS Complementary metal-oxide semiconductor. The CMOS IC is the most popular type of digital IC because of its low powerusage and high immunity to noise.

collector The output terminal of a semiconductor device. Also called a drain.

common base A transistor amplifier in which the circuit shares the base terminal for both inputs and outputs.

common collector A transistor amplifier in which the circuit shares the collector terminal for both inputs and outputs.

common emitter A transistor amplifier in which the circuit shares the emitter terminal for both inputs and outputs.

complementary metal-oxide semiconductor CMOS. The most popular type of digital IC because of its low power usage and high immunity to noise.

demodulate To change the amplitude or frequency of an analog signal.

depleted region The part of a PN junction in which there are no electrons or holes. The depleted region prevents current from flowing.

DIAC Diode alternating current switch. A DIAC can conduct current in either direction, but not until breakdown voltage hasbeen exceeded.

digital IC Digital ICs process only on/off signals. These devices can be found in microprocessors, memory chips, andmicrocomputers.

diode A semiconductor device that acts as a one-way valve for electrical current.

diode alternating current switch DIAC. A semiconductor device that can conduct current in either direction, but not until breakdown voltage has beenexceeded.

diode array A group of diodes arranged in a highly organized manner. Diodes are combined into arrays for greater efficiency andreliability.

DIP Dual-inline package. A popular type of integrated circuit packaging that has two rows of external connecting terminals.

doping The process of changing the conductive properties of silicon by adding trace amounts of other elements.

drain The output terminal of a semiconductor device. Also called a collector.

dual-inline package DIP. A popular type of integrated circuit packaging that has two rows of external connecting terminals.

electrostatic discharge Static electricity that can damage integrated circuits.

emitter The terminal in a semiconductor device that is connected to the source supply of voltage. Also called the source.

ESD Electrostatic discharge. Static electricity that can damage integrated circuits.

FET Field effect transistor. A FET is a semiconductor device that outputs current in proportion to its input voltage. FETs use asmall amount of control current to regulate a larger output current.

fiber optic A filament made of thin, flexible glass or plastic through which light is transmitted. Optical fibers are bundled into groupsto form fiber optic cable.

field effect transistor A semiconductor device that outputs current in proportion to its input voltage. FETs use a small amount of controlcurrent to regulate a larger output current.

flat pack A type of integrated circuit packaging that is extremely thin and flat. A quad flat pack or QFP has leads projecting fromfour sides.

flip-flop circuit A circuit that changes from 1 to 0 or from 0 to 1 when current is applied.

forward bias A condition in which a PN junction allows current to flow in one direction only.

full-wave rectification A type of current conversion that uses both parts of the AC sine wave, both positive and negative, to produce a DC outputwith a single polarity.

gate The input control terminal of a semiconductor device. Also called the base.

gate current A small amount of forward-biased current in the middle PN junction of an SCR that controls a larger amount currentflowing through the SCR.

half-wave rectification A type of current conversion that uses only one half of an AC waveform to convert into intermittent DC. This can be thepositive half or negative half of an AC wave, depending on how the diode is connected to the circuit.

holding current The minimum current which must pass through a semiconductor device in order for it to remain in the ON state.

hole An extra opening in the outer orbital shell of an atom into which an electron can move.



IC Integrated circuit. A miniaturized electronic circuit that combines a variety of components like transistors, resistors,capacitors, and diodes all into one incredibly small piece.

IEC The International Electrotechnical Commission. An international organization that prepares and publishes all standardsfor electrical, electronic, and related technologies.

impedance Resistance to current flow in an AC circuit.

integrated circuit A miniaturized electronic circuit that combines a variety of components like transistors, resistors, capacitors, and diodes

all into one incredibly small piece.

intrinsic semiconductor A type of semiconductor that has a low level of electron movement at any temperature above 0°C (32°F). Silicon is anintrinsic semiconductor.

JFET Junction field effect transistor. A solid state device that can be used as an electronically controlled switch.

leakage current The amount of current required to keep a device active when it is not operating. Also known as load current and residualcurrent.


logic gate A programming function that processes true and false signals.

low current drop A condition that occurs when the current falls below the minimum value required to operate a semiconductor device.

monostable A mode in which a 555 timer produces a single pulse for a preset amount of time in response to an input.

MOSFET Metal oxide semiconductor field effect transistor. A type of transistor that is controlled by voltage rather than current.

multivibrator A device that controls various modes of on/off states in electrical systems. A multivibrator behaves like a pendulummoving back and forth, or a ball bouncing up and down.

NAND A logic function where both A and B must be false to trigger the output. If one input is present, the output will not beturned on.

NOR A logic function where the output will be triggered if neither A nor B are present.

NOT A logic function where the output will not be triggered if a specified input is present.

n-type semiconductor A type of semiconductor that moves current by creating extra electrons that are easily excited into movement.

one-shot A series of timer instructions that creates a delay for only one scan.

OR A logic function where the output is triggered if either A or B are true. OR works similar to a parallel circuit.

oscillator A device that produces a continuous string of on/off pulses at a preset frequency.

PCB Printed circuit board. Semiconductor devices are often mounted on PCBs because the electrical paths on a PCB areperfect for the needs of most semiconductors.

PIN diode A specialized diode that has a layer of intrinsic semiconductor material between the P and N materials. PIN diodes arealso used as photodetectors.

PN junction The area in a semiconductor where P-type and N-type materials are located next to each other. A PN junction allowscurrent to flow in one direction only.

polarity Having a positive or negative charge.

printed circuit board PCB. Semiconductor devices are often mounted on PCBs because the electrical paths on a PCB are perfect for the needsof most semiconductors.

p-type semiconductor A type of semiconductor that moves current by creating holes for the movement of valence electrons.

pulsating DC A type of DC current in which half of the original AC signal wave is blocked, so that the resulting DC signal rises from zeroto a maximum, and then returns to zero.

QFP Quad flat pack. A type of integrated circuit packaging that is extremely thin and flat. A QFP has leads projecting fromfour sides.

quad flat pack A type of integrated circuit packaging that is extremely thin and flat. A quad flat pack or QFP has leads projecting fromfour sides.

rectifier A device that converts AC into DC.

rectify To convert into direct current.

reverse bias A condition in which a PN junction does not allow current to flow.

reverse breakdown voltage The amount of reverse bias that will cause a diode to break down and conduct in reverse.

reverse firing A method of turning off an SCR by applying negative voltage to the gate. Reverse firing requires a high amount of gatecurrent.

sandwich A three-layer NPN or PNP arrangement of semiconductor material.

Schottky diode A specialized diode used in the electronics industry and in radio frequency applications because of its fast switchingspeed and high frequency capability.

SCR A solid state switching device that turns current on and off. SCRs use a small amount of current to switch hundreds ofamps without being damaged.

semiconductor A solid state device that is less conductive than a conductor, but more conductive than an insulator. The most commonsemiconductor material is silicon.

signaling The transmission of electrical signals.

silicon An element from which almost all semiconductors are made.

silicon controlled rectifier A solid state switching device that turns current on and off. SCRs use a small amount of current to switch hundreds ofamps without being damaged.



silicon dioxide A glass-like material that is naturally an excellent insulator. Silicon dioxide is used as the gate insulating material in aMOSFET.

single-phase rectifier A semiconductor device that converts single-phase AC into DC. In a single-phase rectifier, the sine waves produced by theAC power supply reach their peak at 90° simultaneously.

solid state Purely electronic with no moving parts.

source The terminal in a semiconductor device that is connected to the source supply of voltage. Also called the emitter.

substrate The surface or medium that serves as a base for other materials or components.

switching The process of making or breaking an electric circuit, or selecting between multiple circuits.

terminal A connecting point in a circuit to which a wire can be attached to connect a component.

three-phase electric power A type of AC power that is generated with three waveforms that are not in phase with each other.

three-phase rectifier A type of rectifier that uses a three-phase AC electric power source to produce a relatively smooth DC. Three-phaserectifiers provide much smoother DC output voltage than single-phase rectifiers.

thyristor A three-terminal semiconductor switching device. The two main types of thyristors are SCRs and TRIACs.

TO package Transistor-outline package. A type of integrated circuit packaging that is cylindrical in shape and looks like a little can.

TO-5 can A commonly used TO package.

transistor A solid state device that can be used either as an amplifier or as a switch. There are two basic types of transistors:bipolar and field effect.

transistor-outline A type of integrated circuit packaging that is cylindrical in shape and looks like a little can.

TRIAC Triode alternating current switch. A gated switching device that will conduct current in either direction.

triode alternating current switch TRIAC. A gated switching device that will conduct current in either direction.

UJT Unijunction transistor. A voltage-controlled switch that controls current.

unijunction transistor UJT. A voltage-controlled switch that controls current.

valence electron An electron found in the outermost orbit of an atom.

varactor diode A specialized diode that changes its level of capacitance depending on the level of reverse bias applied to the diode. Alsoknown as a varicap diode.

varicap diode A specialized diode that changes its level of capacitance depending on the level of reverse bias applied to the diode. Alsoknown as a varactor diode.

zener diode A specialized diode that is used as a voltage regulator. Zener diodes maintain voltage at a constant, predefined valuewhen they are subjected to reverse voltage.

Photonic semioconductor device:

absorbed Taken in by a substance. Light is absorbed into a dark surface with little or no reflection.

absorption The act or process of suppressing light rays. Absorption can cause signal loss in an optical fiber.

analog A continuously variable signal. Analog signals differ from digital signals in that small fluctuations in the analog signal are meaningful.

anode A positive electrode.

attenuation The loss or decrease of signal power. Fiber optic cables have low attenuation compared to copper cables.

avalanche photodiode A highly light-sensitive type of photodiode.

bandwidth The carrying capacity of a channel. Bandwidth determines how fast data flows through a cable.

bandwidth The amount of information or data that can be sent over a communications channel in a given period of time. The higher a channel'sbandwidth, the more information it can carry.

bending The act or process of changing the direction of light as it passes from one medium to another. Bending can cause signal loss in an opticalfiber.

cathode A negative electrode.

cladding The protective layer surrounding the core of an optical fiber. The cladding protects the core from contaminants, supports the opticalfiber, and reduces loss of light from the core.

copper cable Electric power cables made from twisted pair copper wire.

core The center part of an optical fiber through which light is transmitted.

crystal A solid material with atoms arranged in a highly organized and repeating structure.

dark current The small amount of current that flows through a photonic semiconductor device when it is not operating. Also known as leakagecurrent.

dielectric The stored electrical charge of an object. Dielectric materials conduct no electricity.

diffused light A light ray that is reflected from a surface and broken up and scattered into different directions.

digital Consisting of information that is input or output electronically as a series of pulses or signals either "on" or "off," often resulting inbinary strings of 0s and 1s.

diode A semiconductor device that acts as a one-way valve for electrical current.

discrete A signal that has two states: ON and OFF.

dual inline package A type of semiconductor packaging with two rows of external connecting terminals. Also known as a DIP.

electrical noise An AC power line disturbance caused by sudden changes in the load. Electrical noise is problematic to solid state devices because they



cannot differentiate between an intended electrical pulse and an unintended electrical spike.

electroluminescence A process in which excited electrons emit light. LEDs work through electroluminescence.

electromagnetic energy Energy from a magnetic field that is produced by the motion of electric charges such as electric current.

electromagnetic interference Electrical noise in a circuit that can interrupt or degrade the performance of the circuit. Fiber optic cables are resistant toelectromagnetic interference.

electron A negatively charged particle that orbits the nucleus of an atom. Electrons play an integral role in conducting current.

fiber optic cable A group of individual optical fibers bundled together. Fiber optic cables have higher bandwidth than standard copper cable.

fiber optic receiver A device that amplifies the signal from a transmitter and converts it back into an electrical signal.

fiber optic transmitter A photonic device that converts electrical signals into light signals. The transmitter sends a pulse of light through an optical fiber to thereceiver, where it is converted back into an electrical signal.

fiber optics A technology that transmits light rather than electricity through a fiber made of thin, flexible glass or plastic. Fiber optic cables arereplacing older copper cables for most telecommunications applications.

forward-biased A bias that causes electrons to flow in one direction only. Bias causes an electrical device to operate in a predetermined manner.

high impedance amplifier An amplifier that increases the sensitivity of the receiver.

hole An extra opening in P-type semiconductor material that is available for permitting movement of valence electrons. Holes play anintegral role in conducting current.

infrared emitting diode An LED that emits a wavelength of light below red in the color spectrum. Infrared light is not visible to the human eye.

integrated circuit A complete electronic circuit. Its name resulted from the integration of previously separate transistors, resistors and capacitors, all on asingle chip.

interface circuit A circuit that converts the line voltages between the transmitter and the receiver.

jacket The protective outer layer surrounding the cladding of an optical fiber. The jacket protects the optical fiber from physical damage.

LASCR A light-driven semiconductor device that prevents current flow in either direction until it receives a signal. Also known as a lightactivated SCR.

laser diode A semiconductor device that converts energy into light. Laser diodes have less attenuation than LEDs and use less power.

LCD Liquid crystal display. A light-driven display device made from nematic liquid sealed between two pieces of polarized glass.

leakage current The small amount of current that flows through a photonic semiconductor device when it is not operating. Also known as dark current.


light emitting diode A semiconductor device that emits a narrow spectrum of light in a forward direction. Also known as LED.

light-activated SCR A light-driven semiconductor device that prevents current flow in either direction until it receives a signal. Also known as an LASCR.

light-dependent resistor A type of resistor that decreases in resistance when it is exposed to light. Also known as a photoresistor and a photoconductor.

liquid crystal display A light-driven display device made from nematic liquid sealed between two pieces of polarized glass.

medium A carrier. Air and water are examples of media because they can carry an electrical charge.

millisecond One thousandth of a second.

nanosecond One billionth of a second.

near-infrared light A wavelength below red but above infrared in the color spectrum. Near infrared light can be seen by the human eye.

nematic liquid A substance that is composed of crystals that have the characteristics of both a solid and a liquid. Nematic liquid is used in LCDs.

optical amplifier A device that increases the power of an optical signal without any conversion of the light into an electrical signal.

optical fiber A filament made of thin, flexible glass or plastic through which light is transmitted. Optical fibers are bundled into groups to form fiberoptic cable.

optical isolator A solid state component that uses a light-emitting diode to transmit light through an optically transparent barrier between two isolatedcircuits. This barrier insulates circuits by allowing light to pass through, but not current.

optical source The source of light. The optical source in a fiber optic transmitter is usually an LED or a laser diode.

optocoupler A solid state component that uses a light-emitting diode to transmit light through an optically transparent barrier between two isolatedcircuits. This barrier insulates circuits by allowing light to pass through, but not current.

package A protective cover designed to contain or support a semiconductor device.

photocell A type of resistor that decreases in resistance when it is exposed to light. Also known as photoresistor, light-dependent resistor, andphotoconductor.

photoconductor A type of resistor that decreases in resistance when it is exposed to light. Also known as a photoresistor and a light-dependent resistor.

photodetector A device that senses light. In fiber optic receivers, a photodetector is usually a PIN photodiode or an avalanche diode.

photodiode A light-activated semiconductor device that allows current to flow in only one direction.

photon A particle of light energy.

photonic semiconductor A semiconductor device that uses light in order to create energy. Photonic semiconductors are an integral part of communications andnetworking technology.

photoresistor A type of resistor that decreases in resistance when it is exposed to light. Also known as a light-dependent resistor and aphotoconductor.

phototransistor A semiconductor device that is highly sensitive to light. Photonic transistors are used in switching and amplifying applications, and theycan conduct current in either direction.

phototriac A semiconductor device that uses light to allow small control voltages and currents to switch very high voltages.



photovoltaic cell A small conductive device that can produce an electric current when light shines on the cell.

PIN photodiode A light-sensitive diode that conducts current in one direction only. PIN photodiodes have a fast response time.

pixel An abbreviation for Picture Element. A tiny block of color.

PN junction The part of a semiconductor device where P-type and N-type materials are located next to each other. The PN junction controlsresistance.

polarized glass A type of glass that filters out certain types of light waves. Polarized glass is used on LCD screens.

postamplifier An amplifer in a fiber optic receiver that increases the detector's electrical signal to the level required for further signal processing.

preamplifier An amplifer in a fiber optic receiver that prepares electronic signals for processing by the postamplifier.

PV array A group of photovoltaic cells. PV arrays are used in solar-electric energy systems such as the electrical systems of satellites.

ray A particle of light. Light is made up of rays and waves.

receiver A device that detects and converts signals. Optical fibers are used with receivers to form fiber optic receivers.

reflected light A light ray that bounces off a reflective surface at the exact angle at which it contacted the surface.

refracted light A light ray that is bent into a different direction when it changes speed passing from one medium into another.

resistor A device that controls current by opposing the passage of current.

reverse bias A bias in which heightened resistance prevents current from flowing. Bias causes an electrical device to operate in a predeterminedmanner.

scattering The act or process of reflecting light rays from an object, breaking them up and dispersing the rays into different directions. Scatteringcan cause signal loss in an optical fiber.

semiconductor A solid state device, typically made of silicon, that is less conductive than a conductor, but more conductive than an insulator.

source drive circuit A circuit that improves power conversion efficiency.

splicing The act or process of creating a physical connection betweeen two separate pieces of optical fiber. Optical fibers should only be splicedby a technician who possesses the required skills and interconnection technology.

stimulated emission The creation of additional photons from a single photon. Optical amplifiers use stimulated emission to increase the power of an opticalsignal.

telecommunications The process of transmitting information to a receiver by means of electric current or pulses of light.

thin film transistor A transistor/capacitor hybrid that controls color pixels on an LCD grid.

transimpedance amplifier An amplifer that increases the bandwidth of a signal.

transistor outline A type of semiconductor packaging. Transistor outline packages are usually shaped like a can and are often called TO cans.

transmitter A device that sends signals. Optical fibers are used with transmitters to form fiber optic transmitters.

triac An electronic switch that allows small control voltages and currents to switch very high voltages, as in a lightening controller.

ultraviolet light A wavelength that is above violet in the color spectrum. Ultraviolet light is not visible to the human eye.

visible light Wavelengths of electromagnetic radiation that can be seen with the human eye.

wave The energy that comes from light. Light is made up of rays and waves.

wavelength The distance between separate peaks of a sine wave. The wavelength of light determines whether or not it is visible to the human eye.

zero bias A bias that causes a photodiode to conduct current. Bias causes an electrical device to operate in a predetermined manner.

Limit switches:

active actuation A type of Hall effect sensor actuation in which the sensor is stationary and the magnet is movable. Hall effect sensor actuation maybe active or passive as required by the sensing application.

actuator The part of a limit switch that comes into contact with an object and triggers the switch. Limit switch actuators come in differentstyles: rotary lever, fork, plunger, flexible loop, and spring rod.

amplitude The maximum height or maximum depth of a wave. Amplitude measures the intensity of a signal.

body The part of a limit switch that contains electrical contacts. A limit switch body is a separate, enclosed unit that protects the

circuitry and allows the wiring to stay in place if the head of the switch is replaced

capacitive proximity sensor A type of proximity sensor that senses the stored electrical charge of a target by detecting changes in an electrostatic field.Capacitive proximity sensors are typically used in bulk handling machines, level detectors, and package detection.

capacitor An electrical or electronic part that stores electrical charges.Two metal plates form the capacitor of a capacitive proximity sensor.

contact bounce The action that occurs when electrical contacts close with such force that they slam against each other and bounce away again.Contact bounce is undesirable because it can create secondary arcs and reduce contact life.

contacts Conductive metal parts in an electrical circuit that open or close the circuit by coming in contact with or separating from eachother.

cross-talk Interference between two sensors when the signal from one sensor is unintentionally picked up by another sensor nearby. Cross talkcan cause poor sensor performance or false outputs.



dielectric constant The stored electrical charge of an object.

differential travel The distance between the operating position and release position of a limit switch actuator.

eddy current A magnetic current created by sensor vibration that flows out and around the sensor head.

ferrous metal Made of or containing iron.

flexible loop actuator A type of limit switch actuator that resembles a loop.

fork style actuator A type of limit switch actuator with a two-pronged lever that resembles a "V," with a roller at the top of each end.

free position The starting position of a limit switch actuator before it comes into contact with an object.

gravity return switches A type of limit switch that has no spring return mechanism and requires the weight of the lever arm to reset the contacts. Gravityreturn switches are used on conveyors with small or lightweight objects that require very low forces of operation.

Hall effect sensor A type of proximity sensor that generates voltage in response to the proximity of a magnetic field. Hall effect sensors are used fordetecting metal objects that are among or within other metal objects.

hazardous location switches A class of limit switches used in environments where they may be exposed to corrosive chemicals or possible explosions. Hazardouslocation switches are constructed with thick, heavy materials and use contacts that are encapsulated to avoid electrical energybeing exposed to the elements.

head The top part of a limit switch that holds the actuator. Limit switch heads are removable for easy replacement.

IEC The International Electrotechnical Commission. The IEC governs electrical equipment standards in Europe and all other internationalcountries.

inductive proximity sensor A type of proximity sensor that uses an electromagnetic field to detect metal targets. Inductive proximity sensors are often shieldedto improve sensor output.

limit switch A type of mechanical sensor that requires physical contact to detect the presence or absence of an object. Limit switches are thefirst type of sensor to be used.

maintained actuation A type of limit switch actuation that keeps the actuator at operating position until it is forcibly moved in the opposite direction.

Fork style actuators are used for this type of actuation.

momentary actuation A type of limit switch actuation that rotates the actuator from the free position through all the other positions, until it finallyreturns to the free position. Momentary actuators are spring loaded so that the contacts return to their normal position once theforce is removed.

NEMA The National Electrical Manufacturers Association. NEMA sets standards for equipment used in the United States.

neutral position switches A type of limit switch that allows two different signals and responses, depending on the direction of actuation. When the lever ismoved in a clockwise direction, a set of contacts is actuated. A second set of contacts is actuated when the lever moves in acounterclockwise direction.

operating distance The distance of the sensor from the target while operating. Some sensors have ranges as small as a few millimeters, while otherscan detect objects from hundreds of feet away.

operating position The position that a limit switch actuator reaches before triggering a set of contacts to open or close.

oscillator A type of crystal that creates a constant periodic pulse. Oscillators are often used in solid state and electronic devices.

overtravel position The distance beyond the operating position that a limit switch actuator can move without resetting the contacts.

passive actuation A type of Hall effect sensor actuation in which the sensor is movable and the magnet is stationary. Hall effect sensor actuation maybe passive or active as required by the sensing application.

plunger type actuator A limit switch actuator in the shape of a depressible button or pin.

precision limit switches A class of limit switches used for applications that require repeatable accuracy within a small range. For example, a precision limitswitch would be used to return an electronic scale to its original start position (zero) after an object has been weighed.

pretravel position The distance a limit switch actuator moves between the free position and the operation position.

proximity sensor A solid state device that uses an electronic sensing field to detect the presence of an object. Proximity sensors do not have physicalcontact with the target.

radiated field A field that flows out and around the sensor head in a circular or semicircular pattern.

release position The position that a limit switch actuator reaches midway between the free position and pretravel position.

release travel The distance from the release position back to the free position of a limit switch actuator.

rotary lever actuator A type of limit switch actuator that uses a lever with a roller at the end. The lever can be long or short to suit the application.

safety cable pull switch A type of limit switch that allows the operator to pull on it and stop the machinery in the event of an emergency. Safety cable pullswitches are used in conveyor-type operations where moving parts and machinery may be dangerous to the operator.

safety guard switch A type of limit switch that requires the operator to insert a key into a slot in the switch before the switch will work. Safety guardswitches are used for operating dangerous machines.

sensing field The area of the electronic or magnetic field that forms around the head of a sensor.sensor A device that detects the presence or absence of an object, or certain properties of that object, and provides feedback. Common

sensor applications include parts detection, counting, and positioning, motion, speed, feed, and jam control, and parts diverting.

shunt An opening that allows passage. Shunts in metal devices expose Hall effect sensors to magnetic fields.

solid state device A device that functions by means of electronic components without the use of moving parts.

spring rod actuator A type of limit switch actuator with a long, narrow bar that bends on contact, then bounces back to its original position.

standard industrial limit switches A class of limit switches used in harsh industrial environments where they may be exposed to oil, grease, dirt, shock, vibration, orhigh-pressure washes.

switching rate The speed at which a limit switch opens or closes a set of contacts after initial actuation.

two step switch A type of limit switch set to activate one set of contacts when the lever rotates 10°, and a second set when the lever rotates 20°.



Two step switches are used to detect height, position, and orientation of an object, and they allow a secondary operation.

Ultrasonic::

alkali A non-acidic substance that dissolves in water and increases the pH of a solution. Alkalis can form corrosive salts.

blind zone An area directly in front of the sensor face in which objects cannot be detected because they are too close.

convergent beam scan A photoelectric scanning technique in which a position sensor detector mounted on the receiver measures the angle of light as itbounces off the target and uses this information to suppress backgrounds beyond a specified distance.

dark operate mode A photoelectric scanning mode in which a target is detected when light is blocked from the receiver.

diffuse mode An ultrasonic sensing mode in which the emitter bounces a sound wave off a target. Diffuse mode is the standard mode of operation forultrasonic sensors.

diffuse scan A photoelectric scanning technique in which a small amount of light is transmitted toward a target and the scattered reflected light isused to detect presence.

direct scan A photoelectric scanning technique in which a beam of light shines directly from the transmitter to the receiver. An object is detectedwhen it passes between transmitter and receiver and blocks the beam of light.

electromagnetic interference The disruption of transmission or reception of a signal caused by electrical and magnetic fields.

emitter A fiber optic cable that transmits a beam of light.

excess gain The additional amount of light required by a sensor in a contaminated environment to achieve the same level of detection as in a cleanenvironment.

eye The window or lens of a photoelectric sensor.

fiber optic cable A cable packed with thin, flexible glass or plastic optical fibers that transmit light instead of electricity.

hydraulic fluid A viscous liquid, typically oil, used in industrial applications.

infrared light An area outside of the visible part of the color spectrum, beyond red. Infrared is often used for an invisible wireless connection betweendevices, like TV remote controllers.

light emitting diode A semiconductor device that emits a narrow spectrum of light in a forward direction. Also known as LED.

light operate mode A photoelectric scanning mode in which a target is detected when light from the transmitter reaches the receiver.

load current The current drawn by a sensor when it is energized. Most photoelectric sensors cannot handle more than .5 amps of current.

load-powered Drawing operating current through a load.

minimum holding current The amount of current required for a photoelectric sensor to operate. Most photoelectric sensors need a minimum current of 3 mA to 20mA in order to function properly.

mutual interference Interference between two sensors when the signal from one sensor is unintentionally picked up by another sensor nearby. Mutualinterference can cause poor sensor performance or false outputs.

N-doped Silicon that has been given a negative charge through the addition of other substances.

NPN transistor A transistor with one layer of positively charged semiconductor material between two negatively charged layers.

off-state leakage current Also known as load current and residual current. The amount of current required to keep a sensor active when it is not detecting atarget.

operating current Also known as off-state leakage current and residual current. The amount of current required to keep a sensor active when it is notdetecting a target.

organic solvent Solvents that are organic compounds and contain carbon atoms. The most common organic solvent is water.

P-doped Silicon that has been given a positive charge through the addition of other substances.

photoelectric sensor A type of sensor that detects the presence of an object through the use of a beam of light. Photoelectric sensors have an extremelybroad sensing range, from a few millimeters to 100 feet away.

photoreceiver The part of a photoelectric sensor that detects a beam of light. The phototreceiver may be in a separate unit, or enclosed in the sameunit as the phototransmitter.

phototransmitter The part of a photoelectric sensor that emits a beam of light. The phototransmitter may be in a separate unit, or enclosed in the sameunit as the photoreceiver.

PNP transistor A transistor with one layer of negatively charged semiconductor material between two positively charged layers.

polarized scan A photoelectric scanning technique that uses special filters to absorb glare and reduce or eliminate reflections. Polarized scans filterout all unwanted light sources and detect only depolarized light.

position sensor detector A device mounted on a photoreceiver that determines the distance of a target by measuring the angle of light as it bounces off a target.

radial Radiating outward in all directions from a common center.

receiver A fiber optic cable that receives a beam of light.

reflective scan A photoelectric scanning technique in which light from the transmitter bounces off a reflector placed outside of the housing and travelsback to the receiver. Also known as a retroreflective scan.

reflectivity value A numeric value signifying the amount of light reflected from an object. A white test card has a reflectivity value of 100%, while printednewspaper that absorbs light has a reflectivity value of 60%.



reflex mode An ultrasonic mode of operation in which sound waves are transmitted toward a reflector and bounce back to a receiver. An object isdetected when it passes between the sensor and reflector and blocks the sound waves.

residual current Also known as off-state leakage current and load current. The amount of current required to keep a sensor active when it is notdetecting a target.

retroreflective scan A photoelectric scanning technique in which light from the transmitter bounces off a reflector placed outside of the housing and travelsback to the receiver. Also known as a reflective scan.

scanning The process of detecting changes in the intensity of a beam of light in order to sense an object. Scanning technique is determined bythe distance and physical properties of a target.

semiconductor Silicon crystal that is transformed from an insulator into a conductor. Semiconductors are not as conductive as other materials, such ascopper.

silicon A natural element that forms crystals easily and does not conduct electric current. This makes a silicon an insulator.

solid state relay An electronic switch that contains no moving parts. Solid state relays are rapidly replacing electromechanical relays.

solid state relay An electronic relay with no moving parts.

specular scan A photoelectric scanning technique in which light from the transmitter bounces off a shiny object and travels up to the receiver atexactly the same angle.

switching zone The area the target must enter in order to be detected. The switching zone is determined by the diameter of light emitted from thetransmitter.

target The object or property being detected by a sensor.

thru-beam mode An ultrasonic sensing mode in which the transmitter sends a sound wave toward the receiver. An object is detected when it passesbetween the transmitter and receiver and blocks the sound waves.

thru-beam scan A photoelectric scanning technique in which a beam of light shines directly from the transmitter to the receiver. An object is detectedwhen it passes between transmitter and receiver and blocks the beam of light.

thyristor A solid-state switching device for semiconductors to convert AC current in one of two directions controlled by an electrode.

transistor A device used to amplify a signal or open and close a circuit.

triac An electronic switch that allows small control voltages and currents to switch very large voltages. Triacs conduct in either direction.

ultrasonic sensor A type of sensor that uses sound waves to detect a target. Ultrasonic sensors are the best type of sensor for detecting liquids, clearobjects, or irregularly shaped objects.

viscosity A fluid's resistance to flow. Viscosity is used to describe friction of fluid.

white light Light containing equal amounts of the primary colors. The human eye sees this light as colorless. Sunlight is white light.

Types of motor starting::

across the line Connected directly to the power lines, allowing full voltage when the motor starts.

across-the-line starting A method of motor starting that applies full line voltage to the motor. In this start, the motor is connected directly to the power

source.anode An electrical terminal that usually carries a positive electrical charge. An anode serves as the output terminal in an SCR.

autotransformer starter A type of reduced voltage starter that uses an autotransformer to allow voltage levels to be reduced to 80, 65, and 50% of full linevoltage. Also commonly called a compensator.

autotransformer starting A method of reduced voltage starting that uses a tapped autotransfomer to reduce voltage levels to either 80, 65, or 50% of full linevoltage.

cathode An electrical terminal that usually carries a negative charge. A cathode is common to both the input and output terminals in an SCR.

compensator A term commonly used for an autotransformer starter. A compensator raises current levels to compensate for the reduced voltage.


gate The control terminal in a silicon controlled rectifier. The gate is the input switch that opens or closes the circuit.

generating station The building where the utility company houses large linked AC generators to create the massive power for widespread use.


National Electrical Code The standard for minimum safe electrical installations. The National Electrical Code is adopted in some form as law in all 50 states.

open transition A type of motor circuit that needs to momentarily open the circuit before applying full voltage to the motor. Open transition circuitsare cheaper to use but can cause a current surge when reconnected.

overload protection The use of devices such as overload relays to open the circuit in the event of an overload to prevent the motor from overheating.

part winding motor A type of motor that has two separate sets of primary windings. Part winding motors first energize only half of the windings, then theother half as the motor comes up to speed.

part winding starter A type of reduced voltage starter that applies power to only one set of windings, then to the other set as the motor comes up to speed.

part winding starting A method of reduced voltage starting that applies power to only one set of windings, then to the other set as the motor comes up tospeed.

power distribution system A circuit that travels from generating stations to end users to provide electrical power.

primary resistor starter A type of reduced voltage starter that uses resistors to create an initial 30% drop in voltage before allowing full current to the motor.



primary resistor starting A method of reduced voltage starting that connects resistors in series with the motor to produce an initial 30% voltage drop beforeallowing full current to the motor.

reduced voltage starter A category of motor starters that reduce the power coming into the motor when it is initially started.

rheostat A type of variable resistor that is used to resist electric current. A rheostat is used in DC motor reduced voltage starters.

silicon controlled rectifier A digital switch used to quickly control heavy currents. SCRs are used in solid state reduced voltage starters.

solid state starter A type of reduced voltage starter that uses an SCR to control current levels at startup. Solid state starters have no moving parts, so theyare very durable.

solid state starting A method of reduced voltage starting that uses an SCR to control current levels at startup. This method is expensive, but offers variablevoltage and torque.

squirrel cage induction motor A type of three phase AC motor whose rotor is constructed by connecting metal bars together at each end. It is the most common ACmotor type.

Table 430.7(B) The National Electrical Code table that shows kilovolt amps per horsepower with lock rotor for motors.

tap A wire connected to a specific point on a transformer's secondary winding. This allows the autotransformer to use different turns ratiosto vary voltage.

turns ratio A comparison of the number of turns in the primary versus the number of turns in the secondary. Autotransformers step voltage up ordown based on the turns ratio.

two-point acceleration Having one resistor in series with the motor to provide a smooth start. Adding additional resistors adds additional points of accelerationfor an even smoother start.

voltage drop The reduction in voltage level from the source to the load caused by conductor resistance.

wye-delta starter A type of reduced voltage starter that makes use of the characteristics of wye and delta connections to reduce voltage without loweringcurrent.

wye-delta starting A method of reduced voltage starting that first connects a motor in a wye to reduce voltage, then reconnects the motor in a delta toprovide full line voltage.

Solid state devices

ambient temperature For solid state devices, the temperature of the air inside the equipment enclosure as well as the air outside the enclosure.

analog switching relay A type of solid state relay in which voltage is ramped up in stages after it is applied to the line. Analog switching relays can output anylevel of voltage that the relay is rated to handle.

anode The positively charged terminal of an electronic switch. Anodes are used in solid state components like SCRs to control current.

arcing The act of producing an electric arc. Electric arcs can cause a great deal of damage to electronic equipment, and they are dangerous topeople as well.

brake stop A solid state motor stopping mode that allows the amount of braking to be programmed according to the application. This also affectsbraking time, allowing for a faster stop.

bridging The unintended joining of two or more adjacent pads on a PCB, creating a faulty electronic connection. Condensed moisture can create

bridging between conductors on a PCB.

cathode The negatively charged terminal of an electronic switch. Cathodes are used in solid state components like SCRs to control current.

circuit analysis A troubleshooting method used when a relay fails to turn the load on or off, or operates erratically. Circuit analysis is used when therelay is not suspected as the primary cause of malfunction.

closed loop application An application in which the amount of output is directly proportional to the amount of input signal.

conduit A tubular enclosure for holding wires or cables. Conduits should be used to minimize electrical noise in wires by keeping them separate.

control circuit The part of a solid state relay that determines when the output component is energized or de-energized. The control circuit performsthe same functions in solid state relays as the coupling between the input and output circuits does for electromechanical relays.

control conductor A wire that carries 240 VAC or 460 VAC. Also known as a power wire.

control voltage The minimum voltage required to gate or activate the control circuit of a solid state relay. Also known as pickup voltage.

current limit start A solid state motor starting method that limits the starting current to a programmed value ranging from 50 percent to 600 percent ofthe motor's full load current. This helps to reduce starting torque, which in turn reduces stress on the power distribution system.

diode A solid state device that allows electricity to flow in only one direction.

dip switches Dual In-line Package switch. DIP switches use binary settings, on-off / yes-no, to configure various options on a device.

electrical noise An AC power line disturbance caused by sudden changes in the load. Electrical noise is problematic to solid state devices because theycannot differentiate between an intended electrical pulse and an unintended electrical spike.

electrostatic discharge Current produced by two objects having a static charge when they are brought close enough together to produce an arc or discharge,which appears as static electricity. Electrostatic discharge can destroy small electronic devices.

gate The control terminal of an electronic switch. Gates are used in solid state components like SCRs to control current.

heat sink A conductive metal sheet with large fins that dissipate heat. Heat sinks help protect solid state devices from damage caused by thermalstress.

input circuit The part of a solid state relay to which a control component is connected. The input circuit performs the same function in solid staterelays as coils do for electromechanical relays.

instant-on switching relay A type of solid state relay in which the load is turned on immediately when control voltage is applied to the line. Instant-on relayscontrol inductive loads.



isolation transformer A transformer used to reduce or eliminate electrical noise by modifying the amount of voltage or current on the line.

LED Light-emitting diode. A semiconductor device that emits a narrow-spectrum of light in a forward direction.

light-emitting diode A semiconductor device that emits a narrow-spectrum of light in a forward direction. Also known as an LED.

load switching circuit The load switched by the solid state relay. The output circuit performs the same function in solid state relays as mechanical contacts dofor an electromechanical relay.

maximum load current rating A determination made by the manufacturer as to the highest amount of load current a device can reliably carry.

off-state leakage current The amount of current required to keep a device active when it is not operating. Also known as load current and residual current.

optical isolation A method of controlling solid state relays by using two circuits that are insulated from each other by an optocoupler that convertselectric current to light and then back into electric current.

optical isolator A solid state component that uses a light-emitting diode to transmit light through an optically transparent barrier between two isolatedcircuits. This barrier insulates circuits by allowing light to pass through, but not current.

optocoupler A solid state component that uses a light-emitting diode to transmit light through an optically transparent barrier between two isolatedcircuits. This barrier insulates circuits by allowing light to pass through, but not current.

output circuit The load switched by the solid state relay. The output circuit performs the same function in solid state relays as mechanical contacts dofor an electromechanical relay.

parameter A set of rules, limits, or physical properties that determine the characteristics or behavior of something. In solid state motor starters,parameters may include the trip class, or starting and stopping mode.

peak switching relay A type of solid state relay in which control voltage is applied to the line and the load is turned on when the AC sine wave reaches itspeak. Peak switching is used when voltage and current are out of phase with each other by 90 degrees.

photo-sensitive detector The element of an optical isolator that detects and responds to the light emitted by the LED. Photo-sensitive detectors are used inoptical isolators.

pickup voltage The minimum voltage required to gate or activate the control circuit of a solid state relay. Also known as control voltage.

pump control A solid state motor stopping mode used specifically for centrifugal pumps. This stopping method provides smooth acceleration anddeceleration by reducing surges that occur during starting and stopping.

SCR Silicon controlled rectifier. A diode with an extra junction that forms a gate preventing current flow in either direction until it receivesa voltage signal. Also known as a thyristor.

signal wire A low voltage (usually 10 volts DC or 1-20 mA or less) non-control device used on transducers. Signal wires are for devices that useshielded wires.

silicon controlled rectifier A diode with an extra junction that forms a gate preventing current flow in either direction until it receives a voltage signal. Also knownas an SCR or a thyristor.


soft start A solid state motor starting method that reduces stress on a motor by allowing it to accelerate gradually for a programmed period oftime.

soft start with start boost A solid state motor starting method used for loads that are hard to start in regular soft start mode. Soft start with start boost sends apulse to the motor during startup that provides additional starting torque.

soft stop A solid state motor stopping mode in which deceleration is controlled by the starter instead of the load. Soft stop is used on frictionloads that tend to stop suddenly when voltage is removed from the motor.

solid state device A device that is purely electronic with no moving parts. Solid state devices are generally faster, more reliable, and less expensive than

their electromechanical counterparts.

solid state motor starter A control device that protects a motor from overload by using solid state components instead of contacts to start and stop current flow.Solid state motor starters work more safely and efficiently than mechanical motor starters because they reduce large electrical spikes.

solid state relay An electronic switch that contains no moving parts. Solid state relays are rapidly replacing electromechanical relays.

surge suppressor A device that protects equipment from damaging electrical surges by regulating the voltage on the line.

thermal grease A paste often applied between metal surfaces to increase the conduction of heat between them. Thermal grease should always beapplied between a solid state device and a heat sink.

thyristor A diode with an extra junction that forms a gate preventing current flow in either direction until it receives a voltage signal. Also knownas a silicon controlled rectifier or SCR.

triac An electronic switch that allows small control voltages and currents to switch very large voltages. Triacs can conduct current in eitherdirection.

trip class A numeric rating that correlates to the amount of time it takes to break the circuit when an overload condition occurs. A class 10 relaybreaks the circuit within 10 seconds of overload, a class 20 relay breaks the circuit within 20 seconds of overload, etc.

twisted pair Two insulated copper wires that are twisted around each other to reduce electromagnetic induction from one wire to the other.

varistor A device that protects the relay against overvoltage by diverting high voltages away from sensitive components. A varistor's rating should

be a minimum of 10% higher than the line voltage of the output circuit.

voltage drop The amount of energy used by a device with resistance in the circuit. In a series circuit, voltage drop increases as resistance increases,and decreases as resistance decreases.

voltage spike A sudden, short surge in voltage. Voltage spikes can be caused by lightning, power outages, short circuits, or power transitions in largeequipment on the same power line.

wiring tray A device for organizing and managing multiple electrical wires. Wiring trays should be used to minimize electrical noise in wires bykeeping them separate.

zero switching relay A type of solid state relay in which the load is turned on when the AC sine wave crosses zero. Zero switching relays are used forresistive, inductive, or capacitive loads.



Deaccleration methods

accelerate To increase the rate of speed.

brake fade A reduction in braking effectiveness caused by excessive heat and wearing of components.

brake fluid Hydraulic fluid used in some brake designs. When disk brakes are applied, the hydraulic fluid is sent through the brake lines to the pressure plateor caliper to apply pressure to the rotor and slow or stop motion.

brake pad The anti-friction material that lines plates and calipers used in disk brakes. Brake pads help to reduce heat and increase the life span of brakingelements.

brake shoe Anti-friction material that lines metal plates in brakes. Shoes help to reduce heat and increase the life span of braking elements.

braking Applying some force to cause deceleration.

bridge rectifier A type of full-wave rectifier with four diodes that converts both the positive and negative cycles of AC voltage to DC.

brushes Sliding electrical contacts used to provide a connection between the armature and the external circuit.

caliper A component in disk brakes that holds brake pads and straddles the rotor, pressing against it when the brake is applied to slow and stop motion.Disk brakes with calipers do not create as much heat as brakes with a friction plate.

coasting The natural rate of deceleration of a motor when the power is removed. Coasting is the simplest deceleration method.

contaminant Damaging foreign material such as dirt or shop debris that causes wear to machine components.


counter torque A rotational force that opposes the directional force of torque. Plugging and dynamic braking apply counter torque to a rotor.

DC injection braking Another name for electric braking. Direct current is injected into the system to create constant pole magnetic fields.

decelerate To decrease the rate of speed.

disk brake A friction brake that stops motion when a stationary element is pressed against a rotating disk. Disk brakes are commonly used in automobilesand in some industrial machinery, especially in older machines.

dynamic brake A type of brake that reconnects a motor as a generator. This converts the mechanical motion into electrical energy.

dynamic braking A motor deceleration method that reconnects a motor as a generator. This converts the mechanical motion into electrical energy.

electric brake A non-contact brake design actuated when an electric current charges a coil that acts as an electromagnet. Electric brakes are widely used inautomated machinery and provide a high cycling rate.

electric braking A motor deceleration method that uses DC to create a constant magnetic field.

friction The resistance to motion between the contact surfaces of two objects. Friction generates heat and increases the wear between components butis the key to providing mechanical braking force.

friction brake A brake that engages when two surfaces press together and transfer energy through friction. Friction brakes are the most common typeavailable.

friction plate A stationary disk used in disk brakes to apply pressure to the rotor and slow and stop motion.

inertia The tendency of an object to stay in its state of rest or motion until acted on by an external force. Torque and braking must overcome inertia toaccelerate or decelerate a motor.

mechanical interlock Arranging forward and reverse contacts so that it is physically impossible for both sets of contacts to close at the same time.

off delay timer A delay timer that immediately closes contacts when the control coil is energized, then waits for a predetermined amount of time to open themafter power is removed from the coil.

piston A piece of metal that moves up and down inside a hollow cylinder in response to a pressure change in pneumatic and hydraulic systems. Pistonsmay be used to transfer motion to brake components.

plugging A motor deceleration method that reverses the motor connections so that the motor develops a strong counter torque.

plugging switch A mechanical switch that opens and closes contacts when a motor reaches a set speed. Plugging switches keep the load from reversing once thecounter torque has stopped the load.

rotor The driven, rotating disk in a disk brake that is stopped when pressure is applied by a stationary friction plate or by a caliper.

service factor A measure of the amount of overload a motor can reasonably handle. A service factor of 1.35, or 35% over the rated horsepower withoutoverheating, is required for a motor to be plugged for regular braking.

Acceleration methods::

accelerating torque Another name for pull up torque. It is called accelerating torque because this is the moment at which speed transitions fromstarting speed to full speed.

acceleration The rate at which speed increases.

base speed The speed (in rpm) at which the motor runs with full-line voltage applied to the armature and the field.

breakdown torque The maximum torque a motor can produce without abruptly losing motor speed.

constant horsepower/variable torque A load that requires high torque at low speeds and low torque at high speeds. Horsepower remains constant as speed and torqueare inversely proportional.

constant torque/variable horsepower A load that requires a constant torque throughout acceleration. If the load needs to move faster, the horsepower is increased.



copper loss A power loss due to current flowing through wire. The lost power is converted into heat.


frequency A measurement of the number of complete AC cycles that occurs in one second. Frequency is measured in Hertz (Hz).

friction The resistance to motion between the contact surfaces of two objects. Friction generates heat and increases the wear betweencomponents.

full load torque The torque needed to produce the rated power at the full speed of the motor.

horsepower A unit of power used to describe machine strength. One horsepower equals 33,000 ft-lbs of work per minute, or 746 watts.

inertia The tendency of an object to stay in its state of rest or motion until acted on by an external force. Torque and braking mustovercome inertia to accelerate or decelerate a motor.


locked rotor torque The torque that a motor produces when full power is supplied to the motor and the rotor is not yet moving.

NEMA The National Electrical Manufacturers Association. Motor nameplates carry NEMA letter designations that indicate the designcharacteristics of the motor.

percent slip The difference between a motor's synchronous speed and its speed at full load. Percent slip is a way to measure the speedperformance of an induction motor.

pull up torque The torque needed to cause a load to reach its full rated speed.

rheostat A continuously variable electrical resistor used to regulate current.

speed control The external means of varying the speed of a motor under any type of load.

speed regulation The ability of a motor to maintain its speed when a load is applied. A motor's speed regulation is fixed based on its design.

starting torque Another name for locked rotor torque. It can be called starting torque because it is the torque applied by the motor at startup.

synchronous speed The speed of the rotating magnetic field of an AC induction motor.

torque A force that produces rotation. Torque is measured in pounds-feet in the English system and Newton meters in the metricsystem.

variable frequency drive A device that converts incoming 60Hz AC power into other desired frequencies to allow for AC motor speed control.

variable torque/variable horsepower A load in which both torque and horsepower requirements can change depending on the needed speed.

watt A unit used to measure power. 746 watts equals one horsepower.

actuator The part of a limit switch that transfers the mechanical force of the moving part to the electrical contacts.

air compressor A component that pressurizes ambient air and directs it into a pneumatic system.

automatic input A type of control device that is set to automatically control each step in a process. Pressure switches, flow switches, and temperatureswitches are types of automatic inputs.

bellows A cylindrical device with several deep folds that expand or contract in response to pressure. Bellows are usually used at mediumpressure.

bimetallic sensor A sensor with two unlike metals bonded together. The metals expand at different rates when heated, providing a physical signal thatthe sensor converts into an electrical signal.

capacitive proximity switches Switches that are triggered when they detect either conductive or nonconductive substances.

capillary tube sensor A sensor that changes internal pressure when temperature changes. Capillary tube sensors use temperature sensitive liquid.

chatter The occasional unwanted vibration between components. Chatter decreases productivity and can cause wear.

cold junction The end of a thermocouple that provides a reference point. The cold junction is held at a constant temperature.

contact A conductive part in an electrical circuit attached to a switch that opens or closes a circuit by coming in contact with or separatingfrom the main conductor.

contact block The part of a pushbutton that holds the contacts and is activated when the pushbutton is pressed. The most common pushbuttoncontact block has one NO and one NC contact.



control relay An electrical switch that opens and closes a circuit. Relays can open or close one or many sets of contacts.

deadband pressure The amount of pressure that must be removed before pressure switch contacts reset after the actuation level has been reached.Deadband pressure is also referred to as differential pressure.

diaphragm A deflecting mechanism that moves when reacting to pressure. Diaphragms are usually used at low pressure.

eddy current A magnetic current created by sensor vibration that flows out and around the sensor head.

electrical devices A type of control device that senses the presence of an object without touching it. Electrical devices include proximity switches andphotoelectric switches.

extended button operator A type of pushbutton operator that extends beyond the guard ring. An extended button operator is used when accidental startup is nothazardous.



float A device used in switches that floats on liquid. The float raises or lowers based on the level of the liquid.

flow switches Switches that detect the movement of any fluid, such as liquid, gas, or air in a system. Flow switches are commonly used in fluid pumpsand air compressors.

fluid pump A mechanical device used to move liquids in a hydraulic system.

flush button operator A type of operator that has a guard ring around it to prevent accidental startup.

fork lever actuator A type of actuator that is moved by one of its two roller arms. Fork lever actuators can detect movement in two directions.

guard ring A device around a pushbutton operator that prevents an individual from accidentally pressing the button.

hot junction The end of a thermocouple the measures temperature. The hot junction is exposed to the elements.

hydraulic Power created by the motion and pressure of fluids.

inductive proximity switches Switches that are triggered when they detect a conductive substance.

legend plate The part of a switch that has the written function of the switch's operation. A legend plate often includes the words "start," "stop,""jog," "on," or "off."

level switches Switches that detect the height of a liquid or solid in a tank or another type of vessel. The most common type of level switch is themechanical level switch.

lever actuator A type of actuator that works through a lever connected to the shaft of a limit switch.

light source A beam of light received by a photosensor used to trigger photoelectric switches.

limit switches Switches that detect the presence or absence of an object by physically touching it. Limit switches have a variety of actuators thatcome into contact with an object.

main control station A control panel on a machine that consists of the main pushbuttons and switches that turn the machine on and off and control variousother functions.

manual input A type of control device that requires an individual to manually press a button or turn a switch. Pushbuttons and selector switches are

types of manual inputs.

mechanical devices A type of control device that physically contacts an object. Mechanical devices include limit switches, flow switches, and levelswitches.

mechanical input A type of control device that must touch an object in order to detect it. A limit switch is a type of mechanical input.

mechanical level switch A type of level switch that uses a float that triggers electrical contacts when the liquid reaches a set height.


mushroom button operator A type of pushbutton operator that hangs over the guard in a mushroom shape. A mushroom button operator is easy to press and is usedfor emergency stops.

operator The part of a switch that is pressed, pulled, or turned by an individual operating the circuit. Operators come in a variety of styles andsizes.

paddle A hinged actuator used in many types of flow switches. The flow of fluid deflects the paddle, actuating the flow switch contacts.

photoelectric switches Switches that use a light beam to detect the presence of an object without touching it. Photoelectric switches can detect light objects,heavy objects, or objects that are too hot.

photosensor A type of sensor that detects the presence of an object through the use of a beam of light.

piston A rod inside a cylinder that is moved by hydraulic or pneumatic pressure. Pistons are used at high pressure.

pneumatic Power created by the motion and control of gas, often air, under pressure.

pressure The amount of force exerted on a surface divided by the area of the surface. Pressure is typically expressed in pounds per square inch(psi).

pressure switches Switches that detect a certain amount of force and activate electrical contacts when the force is reached. Pressure switches havedifferent sensing devices that detect pressure changes.

proximity switches Switches that use an electronic sensing field to sense the presence of an object without touching it. Proximity switches can detect thepresence of almost any liquid or solid.

push roller actuator A type of actuator that moves directly forward into the limit switch.


relay An electrical switch that opens and closes a circuit. Relays can open or close one or many sets of contacts.

resistance The opposition to current flow. Electricity flows in the path of least resistance.

resistor A device used in circuits to limit current flow.

selector switches Switches that can be turned to different positions to make a connection with the contacts in that particular position.

sensor A device that detects a change in a physical stimulus and turns it into a signal that can be measured or recorded. All sensors are controldevices, but not all control devices are sensors.

solenoid An output device that converts electrical energy into linear mechanical force.

stop plate A metal guard plate connected to a limit switch that prevents damage to the switch. Stop plates keep limit switches from being forcedbeyond their travel limit.

switch A device that opens and closes a circuit.

temperature switches Switches that react to different heat intensities and activate electrical contacts when the temperature rises or drops below a set level.Temperature switches are often used in heating and cooling systems.

thermistor A resistor that is temperature sensitive. As temperature changes, the resistance of a thermistor changes.

thermocouple A temperature sensor that measures heat at a hot junction and outputs voltage at a cold junction. Thermocouples output voltage that isproportional to the measured temperature.



three-position selector A selector switch that allows you to select one of three circuit conditions. The third position is usually OFF, as in forward/reverse/off.

two-position selector A selector switch that allows you to select one of two circuit conditions. Common two-position selector switches are on/off andforward/reverse.

wobble stick actuator A type of actuator that works through any movement into the switch except a direct pull.

General Definitions Electrical

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