Technical Term in Engineering

8/6/2019 Technical Term in Engineering

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TECHNICAL TERM IN ENGINEERING

Address

A code or number used to reference an area of memory in a PLC.

Algorithm

A software procedure used to solve a particular problem.

Alternating Current

A current (and therefore voltage) that varies over time. Typical power

supplies oscillate as sine waves at either 60Hz or 50Hz. Technically,

at 60 Hz the current is reversing direction 60 times per second.

Analog

A value (such as voltage or current) which can be at any level

between certain limits. With PLCs this typically refers to signals that

range between 0 and 10 volts or 4 to 20mA.

Analog to Digital Converter

Analog to digital converter. A circuit or device that inputs an analog

signal and converts it to a digital value. The resolution refers to

number of bits used to indicate the analog value.

ASCII

American Standard Code for Information Interchange. A code used to

represent common numbers, letters, special symbols and control

codes.


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Assembly Language

Mnemonic commands (typically only three characters) that are one

level above the machine code directly used by the processor. PLC

programming software often has a mnemonic view that correlates

with the ladder diagram.

Back Plane

The printed circuit board at the back of the PLC rack where the

modules connect to a power supply and data bus.

BASIC

A computer language developed by Kemeny & Kurtz in 1964 which

stands for Beginners' All-purpose Symbolic Instruction Code. Some

PLCs have coprocessor cards that use a form of BASIC to perform

computional tasks without affecting the main CPU.

Battery Backup

A battery that allows the memory to retain it's values when the PLC is

turned off.

Baud

The number of times per second a communication transmission

changes the carrier signal. A 2400-baud modem changes the signal

2400 times a second. Baud is technically not the same as bits per

second (bps). For example a 1200 bit-per-second modem actually

runs at 300 baud, but it moves 4 bits per baud (4 x 300= 1200 bits

per second).


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Binary

A base 2 numbering system meaning only the digits 0 and 1 are

used.

Binary Coded Decimal

A PLC coding system in which a word of 16 bits is divided up into four

nibbles (4 bits) and each region used for the decimal range of 0 to 9.

Thus a word will go from 0 to 9999 and can be easily deciphered.

This technique is also used for devices like thumbwheel switches.

Bit

One binary digit. A bit can be either a 1 or 0, either on or off. This is

the smallest piece of information in the PLC. Typically eight bits make

a byte and 16 bits make a word.

Block

A group of bytes or words. A term often used when transmitting or

moving areas of memory.

Block Diagram

An electrical schematic that represents the exact layout of the

components, connections and wiring.

Boolean

A system based on logical states such as AND, OR, NAND, NOR,

NOT and XOR. The symbols can be used singly or in combination to

form circuits that perform true or false operations.


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Branch

A parallel logic path on a ladder logic rung.

Broadcast

A networking term indicating that the message should be sent to all

slaves/clients.

Buffer Memory

A register or group of registers used for temporary storage of data.

Most often used in communication to compensate for different

transmission rates and reception of data.

Bug

Problems in software or hardware design that cause undesired

behavior.

Burn

The process of writing information to PROMmemory. The device that

does the writing is called a burner.

Burn-in

A testing procedure used to run a device at high temperatures to

increase the probability that any component weakness will be

revealed. This ensures that the design is durabile and meets

specifications.


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Bus

In PLCs it is a set of parallel conductors used to deliver information at

a high rate between electronic components. The term is also used for

power distribution connectors.

Byte

A group of bits forming a piece of data. Usually a subset of a word

consisting of eight bits.

Channel

An input or output on a PLC card that requires more then one

connection point. An example is a isolated current signal channel that

requires a positive and negative wire into the PLC card.

Character

A single byte that holds a letter or punctuation.

Chip

A term used for an integrated circuit typically memory.

Clear

The process of removing values or settings from memory.

Closed Loop

A system that measures the output and adjusts operation based on

conditions. This is also known as feedback.


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Compile

The process of translating a program into machine code for the

computer to execute.

Complement

A logical operation that inverts a signal or bit(s). The complement of 0

is 1 and the complement of 1 is 0.

CPU

The Central Processing Unit also refered to as the Processor. The

part of the PLC that runs and interprets the code.

Crosstalk

Signals being induced into other conductors possibly causing

communication errors or false transmissions.

CRT

Cathode Ray Tube. A display device that uses a phosphor coated

screen and one or more electron guns to draw the screen image.

Typically used in TVs and computer monitors but now being replaced

with flat panel displays.

CTS

Clear To Send. Used in serial communications to indicate that the

device can now receive transmissions.


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Current Loop

Use of a 0-20mA or 4-20mA signal over two wires to transmit a value

or state.

Current Sink

A device which permits current to flow to ground when activated.

Current Source

A device that supplies current when activated.

Debounce

Switch and relay contacts bounce on the contacts a few times before

settling down to make a stable electrical connection. Debouncing is

the act of removing or ignoring these initial on/off states.

Debug

The act of locating and eliminating malfunctioning code in a program.

Digital

A value which is discrete, that is, it can only be at certain defined

levels. With PLCs this typically refers to an on or off state like a

switch or relay.

Direct Current

A current (and therefore voltage) that does not vary over time.

Typically a low voltage like 12 or 24 from a battery or power supply.


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Distributed Control System

A system interconnecting sensors, controllers, operator terminals and

actuators to a computer for process automation control. The term

typically refers to proprietary interconnections in contrast to a Process

Automation System.

Double Integer

A number that occupies two consecutive words in memory (32 bits). It

varies from 0 to 4,294,967,295 (in hexadecimal nation from 0 to

FFFFFFFF). A signed double integer goes from -2147483648 to

+2147483647.

Download

Transfer of the program from the computer to the controller.

Driver

A small program running in the background that defines the

configuration settings for software to communicate with a hardware

device.

EEPROM

Electrically Erasable Programmable Read Only Memory is a second

variation of ROM that can be reprogrammed. It is erased electrically

and reprogrammed typically on board without any external device.


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EPROM

Erasable Programmable Read Only Memory is a variation of PROM

that can be reprogrammed once the existing program is erased by

ultraviolet light.

Fieldbus

A fieldbus is a system for serial data transfer in the field area, i.e. the

installation,

sensor/actuator and controller level. Typicall fieldbuses include

PROFIBUS, AS-Interface and InterBus.

Floating Point

Simply put, it's a way of representing numbers with a decimal point

(e.g. 3.0 or 0.003). It is accomplished by using a double word which

holds the sign bit, mantissa and exponent for scientific notation such

as 3 X 10-3. The term Real Number and Floating Point are

equivalent.

Full-Duplex

A bidirectional mode of communication where data may be

transmitted and received simultaneously.

Half-Duplex

A communication link in which data transmission is limited to one

direction at a time.


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Incandescent

Used technically to describe anything that glows with heat.

Incandescent bulbs use a filament heated by electricity to produce

light.

Integer

Used to indicate a whole number in memory. The term is used

independant of the base or radix so it can be in octal, hex or decimal

notation.

Ladder diagram

A circuit diagram used to display electrical control systems like relays

and timers. They consist of power rails on either side with contacts

and coils forming the "rungs of the ladder."

Light Emitting Diode

A semiconductor diode that emits light when biased in the forward

direction. They are typically small domes or square shapped with the

most popular colors being red, green and yellow. They draw less

power then regular incandescent lights but more the LCDs. Some

diplays are made of a matrix of LEDs but they usually are used for

indicator lights.

Liquid Crystal Display

A type of display used typically for text messages which is low cost

and low power but needs a backlight. The technology uses a fluid

between glass which is polarized to block light.


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Logic diagram

An electrical schematic showing the components in a ladder diagram

or using AND,OR and NOT symbols to represent the logical flow of

the controls rather then their real world physical connections.

Long Integer

A number that occupies two consecutive words in memory. It varies

from 0 to FFFFFFFFFFFFFFFF in hexadecimal notation.

LSB

Least significat bit is the rightmost bit or lowest order of a binary

number.

mA

Abbreviation formilliAmps. Milli is a standard metric designation for

1/1000th. Therefore 1 mA = 0.001 Amps.

Mnemonic

A mnemonic is a code, usually from 1 to 5 letters, that represents a

machine code used directly by the processor for commands.

Examples are ADD (add), MUL (multiply), MOV (move).

Modbus

A communication protocol used to share data between controllers. It

was originally designed forModicon PLCs but was adopted by many

other manufacturers since it is an open architecture and thus has

become an industry standard.


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MSB

Most significant bit is the leftmost bit or highest order of a binary

number.

OPC

OPC is a set of standards that specify the communication of data

between software applications and automation hardware. The

acronym OPC originally stood for OLE for Process Control because it

was based upon the Microsoft OLE (Object Linking and Embedding)

technology. In fact, it was meant as the automation industries version

of OLE but with the changes in Microsoft technology the term OLE

has been dropped from the acronym. OPC now stands as a phrase to

describe a set of standards for open connectivity in automation and

process control.

Open Loop

A system that does not monitor the output to adjust control. This is

typically used on well behaved systems.

PID

Acronym forProportional, Integral, Derivative. Control algorithm that

is used to closely control processes such as temperature, mixture,

position, and velocity. The proportional portion takes care of the

magnitude of the error. The derivative compensates for the rate of

error change. The integral takes care of small errors over time.


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Platinum Resistance Thermometers

Platinum Resistance Thermometers. RTDs made of platinum.

PLC

Programmable Logic Controller

Points

The number of possible connections on a PLC card. Usually in

reference to digital inputs and/or outputs. Common numbers of points

are 8,16,32 and 64.

Pre-emptive Multitasking

The ability of a processor to perform multiple tasks which have

priority ratings. The processor performs one task at any given time,

but can be interrupted by the calling of a higher priority task. When

the higher priority task is completed, the processor returns to the

lower priority task that was interrupted.

Process Automation System

A system interconnecting sensors, controllers, operator terminals and

actuators to a computer for process automation control. A PAS is

based on open standards in contrast to a DCS (distributed control

system), which is traditionally proprietary.


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Profibus

A fieldbus standard developed in a government assisted joint

research project in

1987. In 1991, DIN 19245 was adopted, whereby the Profibus

became one of the

first standardised fieldbus systems. This is an open fieldbus standard

covering a

wide area within process and building automation.

Profibus-DP

Profibus Decentralised Peripherals is tailored to the requirements for

a quick, efficient data exchange between automation equipment and

decentralised devices such as binary or analogue input/output

modules and drives for time-critical applications.

Profibus-FMS

Profibus Fieldbus Message Specification is used for messaging

(telegrams) between higher level controls such as PLCs and PCs

where timing is not critical.

Profibus-PA

Profibus Process Automation is a Profibus variant which provides

power on the bus, is intrinsically safe and inter-operable with

Profibus-DP.


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Programmable Controller

An electronic device that can be programmed to control a process or

machine operation. It typically consists of a power supply, processor,

memory, inputs and output.

PROM

Programmable Read Only Memory is a type of non-volatile memory

that can only be written to once but read many times. Unlike ROM

memory this comes from the factory blank so that the user can burn

the contents onto the memory chip. Once the memory is set it cannot

be reprogrammed.

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