226 2 HYDRAULIC, PNEUMAIC AND ELECTRICAL TELEMETRY … · UNIT – 2 HYDRAULIC, PNEUMAIC AND...

UNIT – 2 HYDRAULIC, PNEUMAIC AND ELECTRICAL TELEMETRY

SYSTEMS

1 JN KOTHARI,IC DEPARTMENT

Strength of Hydraulic fluids:

2.1 Industrial: Plastic processing machineries, steel making and primary metal extraction

applications, automated production lines, machine tool industries, paper industries, loaders, crushes,

textile machineries, R & D equipment and robotic systems etc.

2.2Mobile hydraulics: Tractors, irrigation system, earthmoving equipment, material handling

equipment, commercial vehicles, tunnel boring equipment, rail equipment, building and construction

machineries and drilling rigs etc.

2.3 Automobiles: It is used in the systems like breaks, shock absorbers, steering system, wind

shield, lift and cleaning etc.

2.4 Marine applications: It mostly covers ocean going vessels, fishing boats and navel

equipment.

2.5 Aerospace equipment: There are equipment and systems used for rudder control, landing

gear, breaks, flight control and transmission etc. which are used in airplanes, rockets and spaceships.


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COMPONENTS USED IN HYDRAULIC TRANSMISSIONS:

Reservoir:

• All hydraulic systems have a reservoir. A reservoir performs several functions.

• First and foremost, the reservoir holds fluid not required by the system under any

given operating condition and accounts for fluid capacity needs over time in the

system. Fluid volume needs will vary during different operational scenarios

• Secondly, the reservoir provides for thermal expansion of the fluid over the

operational temperature range of the system.

• Thirdly, the reservoir provides fluid to the inlet side of the hydraulic pump.

• Reservoirs consist of a container or volume, fluid inlet port, fluid outlet port,

fill/drain port, and a means to pressurize the fluid in the volume

• Figure shows a mechanical piston reservoir. In this reservoir a spring with an

appropriate preload and a low spring rate pushes on a piston and provides a fairly

constant reservoir pressure.


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• Metal bellows is another (relatively new) type of reservoir. A metal bellows

reservoir would be similar to a metal bellows accumulator. Operation of a metal

bellows accumulator would be similar to a piston/spring reservoir type.

Strainers:

• A strainer is the primary filtering system that removes large particles of foreign

matter from a hydraulic liquid.

• Even though its screening action is not as good as a filter's, a strainer offers less

resistance to flow.

• A strainer usually consists of a metal frame wrapped with a fine-mesh wire screen or

a screening element made up of varying thicknesses of specially processed wire.

Strainers are used to pump inlet lines where pressure drops must be kept to a

minimum.

• Figure -shows a strainer in three possible arrangements for use in a pump inlet line.

If one strainer causes excessive flow friction to a pump, two or more can be used in

parallel. Strainers and pipe fittings must always be below the liquid level in the tank


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Filters:

• Filters are an important part of hydraulic systems. Metal particles are continually

produced by mechanical components and need to be removed along with other

contaminants.

Hydraulic Filter Construction:

• Most hydraulic filters are cylindrical devices with openings for fluid input and

output in opposite sides of the filter.

• Fluid is typically directed through channels in the filter housing and passed

through the filter media.

• The media then collects the contaminants and the cleaned fluid passes through a

central channel between the filter media, making its way to the output.

• The contaminants remain stuck within the filter media; when the filter is full to

capacity, a switch often triggers an LED or other visual indicator to announce that

the filter needs to be changed.

Importance of Hydraulic Filters in a System:

• Fluid contaminants are a leading cause of hydraulic system failure and can cause

numerous problems, including:


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• Mixing of unintended incompatible fluids, causing fluid breakdown and leading to

acid corrosion.

• Internal leakage, lowering component (pump, motor, valve) efficiency and accuracy.

• Particles build up in critical areas, leading to sludge which causes parts to stick.

• Particles build up in close-tolerance areas, leading to component seizure.

• The obvious solution to preventing these problems is to prevent contaminant

particles from cycling through the system. Therefore a clean, efficient filter is

absolutely critical to a hydraulic system

• Most hydraulic systems use mineral oil for the operating media but other fluids such

as water, ethylene glycol, or synthetic types are not uncommon.


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Hydraulic pump:

• Hydraulic pumps are sources of power for many dynamic machines. Hydraulic

pumps are capable of pushing large amounts of oil through hydraulic cylinders or

hydraulic motors. In this fashion, the pump converts the mechanical energy of

the drive (i.e. torque, speed) into hydrostatic energy (i.e. flow, pressure).

• Hydraulic pumps operate according to the displacement principle. This involves

the existence of mechanically sealed chambers in the pump. Through these

chambers, fluid is transported from the inlet (suction port) of the pump to the

outlet (pressure port).

• The sealed chambers ensure that there is no direct connection between the two

ports of the pump. As a result, these pumps are very suitable to operate at high

system pressures and are ideal for hydraulics.

• Hydraulic pumps are manufactured depending on different functional and hydraulic

system requirements, such as operating medium, required range of pressure, type of

drive, etc. A large range of design principles and configurations exists behind

hydraulic pumps.

Centrifugal pump:

• The pumps which employ centrifugal force for conveying liquids from one place to

another are known as centrifugal pumps.

• These pumps are sometimes also called rotodynamic pumps as the liquids are

handled by rotating impeller within a stationary casing.

• The pump is driven by power from an external source by which impeller/rotor is

rotated.

• Here, kinetic energy of the leaving liquid from the impeller is converted into

potential energy.

• When the impeller rotates inside the casing, the liquid is discharged from its centre

by the action of centrifugal force and vacuum is created at the suction eye which is

connected with the suction pipe through which the liquid from reservoir rushes to

the impeller.

• Fig. shows the main element of the centrifugal pump.


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Reciprocating pump:

• The reciprocating pump is a positive displacement pump which operates on the

principle of actual displacement or pushing of liquid by a piston or plunger that

executes a reciprocating motion in a closely fitting cylinder.

• The liquid is alternately drawn from the sump and filled in to suction side of the

cylinder and then led to the discharge side of the cylinder and emptied to the

delivery pipe.

Rotary pump:

• Rotary pumps are positive displacement pumps with the circular motion of the

pumping elements.

• In rotary pumps, the pressure is developed by positive displacement of the liquid.

Rotary pumps are suitable for pumping liquids having low as well as high viscosity.

• The pump can handle vegetable oil, grease, tar, heavy lubricating oil, gasoline,

alcohol, benzene etc. rotary pump consists of fixed casing in which rotating elements

like gears, cams, lobes, screws, vanes etc. are fitted.

TUBES, PIPES AND HOSES:


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• Hydraulic tubes are seamless steel precision pipes, specially manufactured for

hydraulics. The tubes have standard sizes for different pressure ranges, with

standard diameters up to 100 mm. The tubes are supplied by manufacturers in

lengths of 6 m, cleaned, oiled and plugged.

• Hydraulic pipe is used in case standard hydraulic tubes are not available. Generally

these are used for low pressure. They can be connected by threaded connections,

but usually by welds. Because of the larger diameters the pipe can usually be

inspected internally after welding. Black pipe is non-galvanized and suitable

for welding.


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• A hose is a flexible hollow tube designed to carry fluids from one location to another.

Hoses are used when pipes or tubes cannot be used, usually to provide flexibility for

machine operation or maintenance. The hose is built up with rubber and steel layers.

A rubber interior is surrounded by multiple layers of woven wire and rubber.

FITTINGS:

• It is used in pipe plumbing systems to connect straight pipe or tubing sections.

• Fittings serve several purposes;

1) To bridge different standards; O-ring boss to JIC, or pipe threads to face seal, for

example.

2) To allow proper orientation of components, a 90°, 45°, straight, or swivel fitting is

chosen as needed. They are designed to be positioned in the correct orientation

and then tightened.

3) To incorporate bulkhead hardware.

4) A quick disconnect fitting may be added to a machine without modification of

hoses or valves


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Types of fittings:

Pipe fittings:

• Threads on pipe fittings are tapered and rely on the stress generated by forcing the

tapered threads of the male half of the fitting into the female half or component

port.

• pipe threads are prone to loosening when exposed to vibration and wide

temperature variations

Flare-type fittings:

• Tightening the assembly's nut draws the fitting into the flared end of the tubing,

resulting in a positive seal between the flared tube face and the fitting body.

• Tightening the assembly's nut draws the fitting into the flared end of the tubing,

resulting in a positive seal between the flared tube face and the fitting body.

• The flare fittings are designed for use with thin-wall to medium-thickness tubing in

systems with operating pressures to 3,000 psi.


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The Flareless fitting:

• It handles average fluid working pressures to 3,000 psi and is more tolerant of

vibration than other types of all-metal fittings.

• Tightening the fitting's nut onto the body draws a ferrule into the body. This

compresses the ferrule around the tube, causing the ferrule to contact, then

penetrate the outer circumference of the tube, creating a positive seal.

O-ring-type fittings:

• Three basic types now are available: SAE straight-thread O-ring boss fittings, face

seal or flat-face O-ring (FFOR) fittings, and O-ring flange fittings. The choice between

O-ring boss and FFOR fittings usually depends on such factors as fitting location,

wrench clearance, or individual preference.

CONNECTORS:


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Threaded connectors:

• These connectors are used in some low-pressure fluid power systems and are

usually made of steel, copper, or brass, and are available in a variety of designs.

• Threaded connectors are made with standard pipe threads cut on the inside surface.

The end of the pipe is threaded with outside threads. Standard pipe threads are

tapered slightly to ensure tight connections.

Flange connectors:

• Bolted flange connectors are suitable for most pressures now in use. The flanges

are attached to the piping by welding, brazing, tapered threads (for some low-

pressure systems), or rolling and bending into recesses.

Welded connectors:

• The subassemblies of some fluid power systems are connected by welded

joints, especially in high-pressure systems which use pipe for fluid lines.

Brazed connectors:

• Silver-brazed connectors are commonly used for joining nonferrous (copper,

brass, and soon) piping in the pressure and temperature range where their use

is practical. Use of this type of connector is limited to installations in which the


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piping temperature will not exceed 425°F and the pressure in cold lines will not-

exceed 3,000 psi.

Flared connectors:

• Flared connectors are commonly used in fluid power systems containing lines made

of tubing. These connectors provide safe, strong, dependable connections

without the need for threading, welding, or soldering the tubing. The

connector consists of a fitting, a sleeve, and a nut.

• The fittings are made of steel, aluminum alloy, or bronze.

Flareless-tube connectors:


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This type of connector eliminates all tube flaring, yet provides a safe, strong, and

dependable tube connection. This connector consists of a fitting, a sleeve or

ferrule, and a nut.

SEALING DEVICES:

• Seal is relatively soft, non – metallic ring, captured in a groove or fixed in a

combination of rings, forming a seal assembly, to block or separate fluid.

• Fluid power seals are usually typed according to their shape or design. These types

include T-seals, V-rings, O-rings, U-cups and so on.

T-seals:

• The T-seal is always paired with two special extrusion-resisting backup rings,

one on each side of the T. The backup rings T-seals are used in applications

where large clearances could occur as a result of the expansion of the thin-walled

hydraulic cylinder.

V-rings:


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• V-rings can provide excellent service life; otherwise, problems associated with

friction, rod and seal wear, noise, and leakage can be expected.

• The V-ring is the part of the packing set that does the sealing. It has a cross

section resembling the letter V, from which its name is derived.

TYPES OF DIRECTION CONTROL VALVE :

• The directional control valve to extend and retract the main cylinder.

• Directional control valves route the fluid to the desired actuator. They usually consist

of a spool inside a cast iron or steel housing.

• The spool slides to different positions in the housing, and intersecting grooves and

channels route the fluid based on the spool's position.

• The spool has a central (neutral) position maintained with springs; in this position

the supply fluid is blocked, or returned to tank.

• Sliding the spool to one side routes the hydraulic fluid to an actuator and provides a

return path from the actuator to tank.

• When the spool is moved to the opposite direction the supply and return paths are

switched. When the spool is allowed to return to neutral (center) position the

actuator fluid paths are blocked, locking it in position.

• The control valve is one of the most expensive and sensitive parts of a hydraulic

circuit.

• Pressure relief valves, Pressure regulators, Sequence valves, Shuttle valves, Check

valves, Pilot controlled Check valves, Counterbalance valves, Cartridge valves,


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Hydraulic fuses, Auxiliary valves are various types of direction control valves.

TYPES OF ACCUMULATORS:

• An accumulator is a pressure storage reservoir in which hydraulic fluid is stored

under pressure from an external source.

• Four types of accumulators used in hydraulic systems are as follows: 1. Piston type 2.

Bag or bladder type 3. Direct-contact gas-to-fluid type 4. Diaphragm type

Piston type:

• Piston-type accumulators consist of a cylindrical body called a barrel, closures on

each end called heads, and an internal piston.

• Hydraulic fluid is pumped into one end of the cylinder and the piston is

forced toward the opposite end of the cylinder against a captive charge of

air or an inert gas such as nitrogen.

UNIT – 2 HYDRAULIC, PNEUMAIC A


• The orientation of the accumulator and the type of accumulator are

such criteria as available

external monitoring of the

tolerance, seal life, and

and the gas separate.

Bladder-type accumulators:

• Bladder- or bag-type accumulators consist of

inside the shell. See figure

(near the air valve) and

• As a result, the bladder is

accumulator.

• In other words, this type

percentage of the stored

Direct-contact gas-to-fluid

• Direct-contact gas-to-fluid

installations where it would

type accumulator.

2 HYDRAULIC, PNEUMAIC AND ELECTRICAL TELEMETRY

SYSTEMS

JN KOTHARI,IC DEPARTMENT

the accumulator and the type of accumulator are

available space, maintenance accessibility, size, need for

the piston’s location (tail rod indication),

and safety. The purpose of the piston seals is to

type accumulators:

type accumulators consist of a shell or case with a flexible bladder

See figure 9-7. The bladder is larger in diameter

gradually tapers to a smaller diameter at

bladder is capable of squeezing out all the liquid

type of accumulator is capable of supplying

stored fluid to do work.

fluid accumulators:

fluid accumulators generally are used in very large

would be very expensive to require a piston

ND ELECTRICAL TELEMETRY

the accumulator and the type of accumulator are based upon

maintenance accessibility, size, need for

indication), contamination

safety. The purpose of the piston seals is to keep the fluid

a shell or case with a flexible bladder

diameter at the top

at the bottom.

liquid from the

supplying a large

generally are used in very large

piston-or bladder-


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• This type of accumulator consists of a fully enclosed cylinder, mounted in a

vertical position, containing a liquid port on the bottom and a

pneumatic charging port at the top (fig. 9-8).

• This type of accumulator is used in some airplane elevator hydraulic systems where

several thousand gallons of fluid are needed to supplement the output of

the hydraulic pumps for raising the elevator platform.

• The direct contact between the air or gas and the hydraulic fluid tends to entrain

excessive amounts of gas in the fluid.

• For this reason, direct contact accumulators are generally not used for

pressures over 1200 psi.

• The use of this type of accumulator with flammable fluid is dangerous because there

is a possibility of explosion if any oxygen is present in the gas, and pressure surges

generate excessive heat. For this reason, safety fluids are used in this type of

installation.

Diaphragm accumulators:

• The diaphragm-type accumulator is constructed in two halves which are either

screwed or bolted together.

• A synthetic rubber diaphragm is installed between both halves, making two

chambers. Two threaded openings exist in the assembled component.

• An air valve for pressurizing the accumulator is located in the gas chamber end of

the sphere, and the liquid port to the hydraulic system is located on the opposite

end of the sphere.


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• This accumulator operates in a manner similar to that of the bladder-type

accumulator.

COMPONENTS USED IN PNEUMATIC TRANSMISSIONS:

Pneumatic System Components:

1. Compressor

2. Air tank (reservoir)

3. Dryer/Separator

4. Air filter/Regulator/Lubricator

5. Accumulator

6. Direction control valve

7. Actuator


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Compressor:

• A compressor can compress air to the required pressures. It can convert the

mechanical energy from motors and engines into the potential energy in compressed

air.

A single central compressor can supply various pneumatic components with

compressed air, which is transported through pipes from the cylinder to the

pneumatic components.

1 According to the design and principle of operation

1. Reciprocating compressor

2. Rotary screw compressor

3. Turbo Compressor

2. According to the number of stages

1. Single stage compressor

2. Two stage compressor

3. Multi stage compressor

3. According to the pressure limits

1. Low pressure compressors

2. Medium pressure compressors

3. High pressure compressors

4. Super high pressure compressors

4. According to the capacity

1. Low capacity compressors

2. Medium capacity compressors

3. High capacity compressors

5. According to the method of cooling

1. Air cooled compressor


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• Water cooled compressor

• Compressors can be divided into three classes: centrifugal, reciprocatory and rotary.

ROTARY COMPRESSOR RECIPROCATING

COMPRESSOR

CENRTIFUGAL

COMPRESSOR

A

D

V

A

N

T

A

G

E

1. Simple design

2. Low cost

3. Easy maintenance

4. Easy to install

5. Few moving parts

1. Simple design

2. Low initial cost

3. Easy to install

4. High efficiency in

two stage model

1. High efficiency

2. Design to give

lubricant free air

3. Also used for high

pressure

4. Relatively low cost

as size increase

DIS-

A

D

V

A

N

T

A

G

E

1. Low efficiency

2. Difficulty with

dirty environment

1. Higher

maintenance cost

2. Many moving

parts

3. Vibration problem

may occurs

4. Available in

limited size

1. High initial cost

2. Complicated

control system

3. Special

maintenance required

Centrifugal compressor

In the case of where flow simply passes through a straight pipe to enter a centrifugal

compressor; the flow is straight, uniform and has no vortices. As illustrated below α1 = 0°.] As

the flow continues to pass into and through the centrifugal impeller, the impeller forces the

flow to spin faster and faster. According to a form of Euler's fluid dynamics equation, known as

pump and turbine equation, the energy input to the fluid is proportional to the flow's local

spinning velocity multiplied by the local impeller tangential velocity.

In many cases the flow leaving centrifugal impeller is near the speed of sound (340

metres/second). The flow then typically flows through a stationary compressor causing it to


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decelerate. These stationary compressors are actually static guide vanes where energy

transformation takes place. As described in Bernoulli's principle, this reduction in velocity

causes the pressure to rise leading to a compressed fluid.

Accumulator:

• The most common use for accumulators is to supplement pump flow. Some process

requires high-volume flow for a short time and then uses little or no fluid for an

extended period.

• Stores compressed air,

• Prevents surges in pressure

• Prevents constant Compressor operation (“duty cycles” of Compressor)


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Check valve:

• One-way valve -allows pressurized air to enter the pneumatic system, but prevents

backflow of air toward the Compressor when Compressor is stopped (prevent loss of

pressure)

Direction control valve:

• Controls pressurized air flow from Accumulator (source to user equipment via

selected port

• Some valves are one way –shut tight

• Some valves are two way, allowing free exhaust from the port not selected

–valves can be actuated manually or electrically

Actuator:

• Converts energy stored in compressed air into mechanical motion

• Example is a linear piston (piston limited to moving in two opposing directions)

• Other examples are alternate tools including: rotary actuators, air tools, expanding

bladders, etc

Components of Electrical telemetry system:


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ENCLOSURE & JUNCTION BOXES:

• When one spark makes the difference between a normal day and a big problem,

enclosures are an absolute necessity.

• Designed to fully contain and confine an explosive force within the enclosure, they

are strong enough to withstand the effects of corrosion and time.

• Enclosures and Junction Boxes are for use in industrial locations where safety and

productivity depends on protection against hazardous atmospheres and dusts,

corrosive conditions and adverse weather

• Enclosures protect electronic, mechanical, hydraulic and pneumatic instruments and

associated equipment from the damaging effects of high winds, rain, snow and sub-

zero conditions, both onshore and offshore, so extending their operational life,

protecting capital investment and minimizing equipment maintenance and service

costs.

• Process measurements are maintained at consistent levels through the thermal

stability offered by the enclosure.

• Enclosures can be fitted with a number of options including: viewing windows,

heaters/thermostats, junction boxes, isolators, vents, and thermal insulation

materials and are able to accommodate a comprehensive range of integral base or

back mounted instrument manifolds.

NUMBERING AND TAGGING SYSTEM:

• To avert the problems inherent in the above example, many process industries

utilize a numeric-only system for tagging equipment.

• This helps simplify the logical categorization of equipment during the process design

phase.

• Moreover, a structured tag system is more intuitive for the development of design

documentation, operating procedures and training, and general documentation

upkeep/maintenance.

• With that in mind (and considering the points presented earlier in this Part), the

following method is but one example of how to tag process equipment using an

extensible system.


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Area Number, AN:

• Most sizable process plants are comprised of multiple areas. An area is a physical,

geographical, or logical grouping determined by the site.

• It may contain process cells, units, equipment modules, and control modules. To

facilitate a hierarchical organization of equipment, equipment tags should then

incorporate area designation.

• A small or simple project may have only one area. Conversely, larger more complex

projects may have multiple areas.

• The assignment of areas is at the discretion of the process engineer and can be

subjective.

• The only general rule that I like to employ is that common equipment that serves

multiple areas, e.g., utility and infrastructure system be placed into a “Common

Resources” area rather than be made a part of any other process area.


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• Once areas have been designated for a particular project type, engineers should

strive to maintain common area designations on future, similar projects.

• For example, the areas shown in the figure above may be defined on the lead sheet

for a fictitious project.

Equipment Types, ET:

• Equipment can be identified based on its type using a numeric system such as the

simple one shown below. In cases where equipment has multiple functions, user

discretion is advised in selecting the most suitable type code.

Sequence Number, SQ

• This is the consecutive numbering of like equipment in a particular area. The

sequence begins with 01. All equipment is to a have its own sequence number. The

use of alphabetic or other tag suffixes is to be avoided.


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CABLES:

• Unshielded Twisted Pair (UTP) Cable

• Shielded Twisted Pair (STP) Cable

• Coaxial Cable

• Fiber Optic Cable

Unshielded twisted pair cable:

• It is the most common type of telecommunication medium in use today.

• It is mostly used in telephone system.

• As shown in fig. twisted pair consists of two conductors, each with its own colored

plastic insulation.

• One potential problem of UTP is that its wire can be affected by electromagnetic

interference from devices, which can create a noise over wires which can damage

the signal.

Advantages:

• Low cost

• Easy to use

• Cheap and flexible

• Easy to install

Shielded twisted pair cable:

• STP cable has a metal foil or braided mesh covering that enclosed each pair of

insulated conductors, which are a higher quality and more protective jacket than

UTP has.

• This gives STP excellent insulation to protect the transmitted data from outside

interference.

• STP is less susceptible to electrical interference and supports high transmission rates

over longer distance than UTP.

Co – axial cable:


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• Co – axial cable has better shielding than twisted pairs, so it can span longer

distances at higher speed.

• Co – axial cable carries signals of high frequency range than twisted pair cable.

• In fig., co – axial cable has a central core conductor of solid or standard wire

enclosed in an insulating sheath.

• It is enclosed in an outer conductor of metal foil, braid or a combination of two.

• The outer metallic wrapping serves both as a shield against noise and as the second

conductor, which complete the circuit.

• This outer conductor is also enclosed in an insulating sheath and the whole cable is

protected with a cplastic cover.

Advantages:

• Easy to install.

• Flexible and easy to work with.

• Transmit data at longer distance and relatively high speed.

• Low cost.

• Light weight.

FIBER OPTIC CABLE:

• Fig. shows the fiber optic cable.

• At the center is the glass core through which light propagates.

• A core is surrounded by glass cladding.

• A thin plastic jacket is used to protect the cladding.

• Two types of light sources can be used for signaling LED and lasers.

Advantages:

• Fiber is much lighter

• It can’t affect noise

• Immunity to electromagnetic

• Electrical insulator

Disadvantages:


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• High cost

• Propagation of light is unidirectional

• Glass fiber is easily broken

CONNECTORS:

Unshielded Twisted Pair Connector:

• The standard connector for unshielded twisted pair cabling is an RJ-45 connector.

This is a plastic connector that looks like a large telephone-style connector

• A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack,

implying that the connector follows a standard borrowed from the telephone

industry. This standard designates which wire goes with each pin inside the

connector.

Fig. 2. RJ-45 connector

Coaxial Cable Connectors:

• To connect coaxial cable to devices, we need coaxial connectors. The most common

type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC)

connector.

• Fig. shows three popular types of these connectors: the BNC connector, the BNC T

connector, and the BNC terminator.

• The BNC connector is used to connect the end of the cable to a device, such as a TV

set. The BNC T connector is used in Ethernet networks to branch out to a connection

to a computer or other device. The BNC terminator is used at the end of the cable to

prevent the reflection of the signal.

Fiber optic connectors:


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• There are three types of connectors for fiber optic cables, as shown in fig.

• The subscriber channel (SC) connector is used for cable TV. It uses a push/pull locking

system.

• The straight tip (ST) connector is used for connecting cable to networking devices. It

uses a bayonet locking system and is more reliable than SC. MT – RJ is a connector

that is same size as RJ 45.

CLAMP:

• A clamp is a fastening device to hold or secure objects tightly together to prevent

movement or separation through the application of inward pressure.

• There are many types of clamps available for many different purposes. Some are

temporary, as used to position components while fixing them together, others are

intended to be permanent.

INDUSTRIAL SAFETY:

• Industrial safety is primarily a management activity which is concerned

with reducing, controlling and eliminating hazards from the industries or industrial

units.

Importance of industrial safety:

• T h e d a n g e r o f l i f e o f h u m a n b e i n g i s i n c r e a s i n g w i t h a d v a n c e

m e n t o f s c i e n t i f i c development in different fields.

• The importance of industrial safety was realized because every millions of

industrial accidents occur which result in either death or in temporary

disablement or permanent disablement of employees and involve large

amount of losses resulting from danger to property, wasted man hours and

wasted hours.


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• M o r e e v e r , f r o m m a n a g e r i a l p e r sp e c t i v e th e i mp or ta nc e o f i n d u s tr

i a l sa fe t y i n a n y organization may be concluded by following facilitation:

• T r e a t m e n t : i n d u s tr i a l s a f e t y ma n a g e m e n t p r o v i d e s t r e a t me n t

f or i n ju r i e s a n d illness at the work place.

• M e d i c a l E x a m i n a t i o n : i t c a r r i e s o u t m e d i c a l e x a m i n a t i o n o f

s t a f f j o i n i n g t h e organization or returning to work after sickness or accident.

• H a z a r d s i d e n t i f i c a t i o n .

• P r o v i s i on o f p r o te c t i v e d e v i c e s .

• Consultancy: it provides medical advised on other condition potentially

affecting health e.g. works canteen etc.

• Education: it provides safety and health training

ELECTRICAL ISOLATION:

OPTICAL ISOLATION:

• Optical isolation is done by optical isolator.


SYSTEMS


• An optical isolator, or optical diode, is an optical component which allows the

transmission of light in only one direction.

• It is typically used to prevent unwanted feedback into an optical oscillator, such as

a laser cavity. The operation of the device depends on the Faraday effect (which in

turn is produced by magneto-optic effect), which is used in the main component,

the Faraday rotator.

• The need for optical isolation has broadened considerably since the advent of lasers.

It is often necessary to prevent light from reentering the laser, irrespective of any

electrical consideration.

• One example is a small laser followed by high-power laser amplifiers. If the powerful

amplified light reenters the small (master oscillator) laser, it can destroy it.

• Another example is a frequency-stabilized laser, whose oscillation frequency

is perturbed by reentering (injected signal) light.

PROCEDURE TO TEST ELECTRIC ISOLATION:

• An electrical isolation test is a direct current (DC) resistance test that is performed

between sub circuit common and subsystem chassis to verify that a specified level of

isolation resistance is met.

• Isolation resistance measurements may be achieved using a high input

impedance ohmmeter, digital multimeter (DMM) or current-limited test instrument.

The selected equipment should not overstress sensitive electronic components

comprising the subsystem.

• The test limits should also consider semiconductor components within the

subsystem that may be activated by the potentials imposed by each type of test

instrumentation.

• A minimum acceptable resistance value is usually specified (typically in the mega

ohm (MΩ) range per circuit tested). Multiple circuits having a common return may

be tested simultaneously, provided the minimum allowable resistance value is based

on the number of circuits in parallel.

• Five basic isolation test configurations exist:[1]

1. Single Unreferenced End-Circuit - isolation between one input signal and circuit

chassis/common ground.

2. Multiple Unreferenced End-Circuits with a single return - isolation between

several input signals and circuit chassis/common ground.


SYSTEMS


3. Subsystem with Isolated Common - isolation between signal input and common

ground.

4. Common Chassis Ground - isolation between circuit common and chassis (chassis

grounded).

5. Isolated Circuit Common - isolation between circuit common and chassis (chassis

floating).

Isolation measurements are made with the assembly or subsystem unpowered and

disconnected from any support equipment.

226 2 HYDRAULIC, PNEUMAIC AND ELECTRICAL TELEMETRY … · UNIT – 2 HYDRAULIC, PNEUMAIC AND...

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