Hemant Pathak

7/28/2019 Hemant Pathak

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NATIONAL FERTILIZERS LIMITED

VIJAIPUR GUNA (M.P.)

REPORT ON

VOCATIONAL TRANING

At

(AMMONIA 1 (INSTRUMENTATION))

SUBMITTED TO SUBMITTED BYMr. D. R. Chowdhary(Chief Manager HRD)Mr. R. P. Gupta(Asst. Manager HRD)

Hemant Pathak B. Tech (2 nd Year)

Electronics &Communication


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ACKNOWLEDGEMENT

I deeply acknowledge my sense of quietude to honorable Mr. D. R.Chowdhary (Chief Manager HRD) Mr. R. P. Gupta (Asst. Manager HRD)and staff for arranging my vocational training in their esteemed organization.

I would also like to express my heartily thanks and indebtedness to

Mr. B. Roy (S. R. Manager)

Mr. R. Boipai (Manager)

Mr. Sudesh Kumar (Dy. Manager)

Mr. Shiv Prasad (Asst. Manager)

Mr. Anshul Jain (Asst. Manager)

Mr. A.K. Dwivedi (Asst. Manager)

For their deep involvement, invaluable suggestion and continues motivationthroughout this period. I am highly obliged to them for always being there inmy needs.

I cannot escape by giving thanks to all people directly or indirectly helpingme for the completion of my training.


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AMMONIA PROCESS DESIGN

Ammonia is produced from a mixture of hydrogen and nitrogen in a proportion of approximately 3:1.

Natural gas from Gail is used as the major fuel for urea production. Hydrocarbon feed is completely desulphurized in the desulphurization

section. The desulphurized hydrocarbon is reformed with steam and atmospheric air

into process gas in the Primary and Secondary Reformer.

The gas contains mainly hydrogen, nitrogen, carbon monoxide and carbondioxide. After that carbon monoxide is converted to carbon dioxide and hydrogen

with steam to increase the yield of hydrogen. Then carbon dioxide is then absorbed in GV Section and the sent to

ammonia synthesis chamber. The remaining carbon dioxide is then converted to methane in methanator

using hydrogen.

The purified synthesis gas is compressed to about 220 kg/cm2 and sent tothe ammonia synthesis loop where it is converted into ammonia. This formed ammonia is then sent to urea plant for production of urea or

sent to ammonia storage unit after passing it from cooling tower (which hasa capacity of storing 10000MT).

The flow diagram is shown below.


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CH 4 CO, CO 2, H 2

CO 2, H 2, N 2 CO, CO 2, H 2, N 2

H 2, N 2

Desulphurizationtank

NaturalGas form

GAIL

PrimaryReformer

Secondary

Reformer

GVSection

CO to CO2Converter

Steam

Atmospheric

Air

Absorbed CO2 to UREAPLANT

SynthesisCompressor NH3 Reactor

Ammonia to Urea Plant orto Storage Unit


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INSTRUMENTATION

The Technology of using instruments to measure and control the chemical and physical properties of materials is called Instrumentation.

It is a tool for efficient plant operation in any process industry. Efficiency meansincreased productivity, cost reduction and increased profitability of operation.When the instruments are used for the measurement and control of industrialmanufacturing conversion process is known as process instrumentation.

The role of instruments in particularly very pivotal in a fertilizer industry.Where instruments has to keep pace with the new developments to measure ,record, analyze and control the highly complex chemical reaction, unit operationtaking place at high pressure and temperature.

Process plant consists of hundreds or even thousands of control loops allnetworked together to produce to be offered for sale. Each of these is controlledwithin a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates disturbance that detrimentally affect the

process variables and interaction from other loops in the network providesdisturbances that influence the process variable.

To reduce the effect of these load disturbance sensor the transmitter collectinformation about the process variable and relationship to some desired set point.

This simple process control loop consists of these elements:-

1. Sensing2. Measurement3. Controlling element

4. Final control element


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MEASUREMENT

Measurements have got to be one of the most important equipment in any processing plant. Any decision made on what the plant should do is based on what

the measurement tell us.It is the integrated approach of application of knowledge, skill, standard practicesto keep all the equipments / Instruments in healthy condition with their reliability,accuracy, for efficient & trouble free optimum operation of the plant

In the context of process control, all controller decision is similarly passedon measurement. This section is going to deal with the instrument equipmentnormal used to measure and provide signals. We will look at the measurement of these process parameters.

Pressure Flow Level Temperature Vibration

PRESSURE

General Theory

Pressure is probably one of the most commonly measured variables in the process plant. It includes the measurement of steam pressure; feed water pressure,condenser pressure, process fluids, lubricating oil pressure and many more.Pressure is actually the measurement of force acting on area of surface. We couldrepresent this as:

The units of measurement are either in pounds per square inch (PSI) in Britishunits or Pascals (Pa) in metric. As one PSI is approximately 7000 Pa, we often usekPa and MPa as units of pressure.


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Pressure Measurement

The object of pressure sensing is to produce a dial indication, control operation or a standard (4 - 20 mA) electronic signal that represents the pressure in a process.

Common Pressure Detectors

Bourdon Tubes

Bourdon tubes are circular-shaped tubeswith oval cross sections. The pressure of the medium acts on the inside of the tube.The outward pressure on the oval crosssection forces it to become rounded.

Because of the curvature of the tube ring,the bourdon tube then bends as indicated inthe direction of the arrow.

Due to their robust construction, bourdonare often used in harsh environments andhigh pressures, but can also be used for very low pressures; the response timehowever, is slower than the bellows or diaphragm.

Differential Pressure Transmitters

Most pressure transmitters are built around the pressure capsule concept. They are usually capableof measuring differential pressure (that is, thedifference between a high pressure input and a low

pressure input) and therefore, are usually called DPtransmitters or DP cells. Figure illustrates a typicalDP transmitter. A differential pressure capsule is

mounted inside housing. One end of a force bar isconnected to the capsule assembly so that themotion of the capsule can be transmitted to outsidethe housing. A sealing mechanism is used where the force bar penetrates thehousing and also acts as the pivot point for the force bar. Provision is made in thehousing for highpressure fluid to be applied on one side of the capsule and low-


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pressure fluid on the other. Any difference in pressure will cause the capsule todeflect and create motion in the force bar. The top end of the force bar is thenconnected to a position detector, which via an electronic system will produce a 4 -20 ma signal that is proportional to the force bar movement.

DP Transmitter Application

A DP transmitter is used to measure the gas pressure (in gauge scale) inside avessel. In this case, the low-pressure side of the transmitter is vented toatmosphere and the high-pressure side is connected to the vessel through anisolating valve. Theisolating valve facilitatesthe removal of thetransmitter. The output of the DP transmitter isproportional to the gaugepressure of the gas, i.e., 4mA when pressure is 20kPa and 20 mA whenpressure is 30 kPa.

STRAIN GAUGES

The strain gauge is a device that can be affixed to the surface of an object todetect the force applied to the object. One form of the strain gauge is a metalwire of very small diameter that is attached to the surface of a device beingmonitored.


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For a metal, the electrical resistance will increase as the length of the metalincreases or as the cross sectional diameter decreases. When force is applied asindicated in Figure 8, the overall length of the wire tends to increase while thecross-sectional area decreases. The amount of increase in resistance isproportional to the force that produced the change in length and area. Theoutput of the strain gauge is a change in resistance that can be measured by theinput circuit of an amplifier. The change in the process pressure will cause aresistive change in the strain gauges, which is then used to produce a 4-20 mAsignal.


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FLOW MEASUREMENT

There are various methods used to measure the flow rate of steam, water,lubricants, air, etc., in a nuclear generating station. However, in this module will

look at the most common, namely the DP cell type flow detector. Also in thissection we will discuss the application of a square root extractor and cut-off relayplus the possible sources of errors in flow measurements and different failuremodes that can occur.

Flow Detectors

Orifice Plate

The orifice plate is the mostcommon form of restrictionthat is used in flowmeasurement. An orificeplate is basically a thin metal

plate with a hole bored in thecenter. It has a tab on one sidewhere the specification of the plate is stamped. The upstream side of the orificeplate usually has a sharp, edge.

With an orifice plate in the pipe work, static pressure increases slightly upstreamof the orifice (due to back pressure effect) and then decreases sharply as the flowpasses through the orifice, reaching a minimum at a point called the venacontracta where the velocity of the flow is at a maximum. Beyond this point,static pressure starts to recover as the flow slows down. However, with an orificeplate, static pressure downstream is always considerably lower than the upstreampressure. In addition some pressure energy is converted to sound and heat due tofriction and turbulence at the orifice plate. Figure shows the pressure profile of anorifice plate installation.


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Advantages and Disadvantages of Orifice Plates

Advantages of orifice plates include:

High differential pressure generated

Exhaustive data available

Low purchase price and installation cost

Easy replacement

Disadvantages include:

High permanent pressure loss implies higher pumping cost.

Cannot be used on dirty fluids, slurries or wet steam as erosion will alter thedifferential pressure generated by the orifice plate.


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LEVEL MEASUREMENT

Accurate continuous measurement of volume of fluid in containers has alwaysbeen a challenge to industry. This is even more so in the nuclear station

environment where the fluid could be acidic/caustic or under very highpressure/temperature. We will now examine the measurement of fluid level invessels and the effect of temperature and pressure on this measurement. We willalso consider the operating environment on the measurement and the possiblemodes of device failure.

Open Tank Measurement

The simplest application is the fluid level in an open tank. Figure shows a typical

open tank level measurement installation using a pressure capsule leveltransmitter

Closed TankMeasurement

Should the tank beclosed and a gas orvapour exists ontop of the liquid,


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the gas pressure must be compensated for. A change in the gas pressure willcause a change in transmitter output. Moreover, the pressure exerted by the gasphase may be so high that the hydrostatic pressure of the liquid column becomesinsignificant. For example, the measured hydrostatic head in a boiler may beonly three meters (30 kPa) or so, whereas the steam pressure is typically 5 MPa.Compensation can be achieved by applying the gas pressure to both the high andlow-pressure sides of the level transmitter. This cover gas pressure is thus used asa back pressure or reference pressure on the LP side of the DP cell. One can alsoimmediately see the need for the three-valve manifold to protect the DP cellagainst these pressures.

Effect of Temperature on Level Measurement

Level measu rement systems that use differential pressure P as the sensingmethod, are by their very nature affected by temperature and pressure. Recallthat the measured height H of a column of liquid is directly proportional to thepressure P exerted at the base of the column and inversely proportional to thedensity of the liquid.

H P/

Density (mass per unit volume) of a liquid or gas is inversely proportional to itstemperature.

1/ T

Thus, for any given amount of liquid in a container, the pressure P exerted at thebase will remain constant, but the height will vary directly with the temperature.

H T


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Effect of Pressure on Level Measurement

Level measurement systems that use differential pressure P as the sensingmethod, are also affected by pressure, although not to the same degree as

temperature mentioned in the previous section.

Again the measured height H of a column of liquid is directly proportional to thepressure PL exerted at the base of the column by the liquid and inverselyproportional to th e density of the liquid:

H PL/

Density (mass per unit volume) of a liquid or gas is directly proportional to theprocess or system pressure Ps.

Ps

Thus, for any given amount of liquid in a container, the pressure PL (liquidpressure) exerted at the base of the container by the liquid will remain constant,but the height will vary inversely with the process or system pressure.

H 1/Ps

Most liquids are fairly incompressible and the process pressure will not affect thelevel unless there is significant vapour content.


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TEMPERATURE MEASUREMENT

Every aspect of our lives, both at home and at work, is influenced by temperature.Temperature measuring devices have been in existence for centuries. The age-old

mercury in glass thermometer is still used today and why not? The principle of operation is ageless as the device itself. Its operation was based on thetemperature expansion of fluids (mercury or alcohol). As the temperatureincreased the fluid in a small reservoir or bulb expanded and a small column of the fluid was forced up a tube. You will find the same theory is used in manymodern thermostats today. In this module we will look at the theory andoperation of some temperature measuring devices commonly found in agenerating station. These include thermocouples, thermostats and resistive

temperature devices.

Thermocouples (T/C) and resistive temperature devices (RTD) are generallyconnected to control logic or instrumentation for continuous monitoring of temperature. Thermostats are used for direct positive control of thetemperature of a system within preset limits

TEMPERATURE MEASURING INSTRUMENTS:-

1. Mercury in Glass Thermometers.

2. Bimetallic Thermometers.

3. Pressure-Spring Thermometers.

4. Thermocouples.

5. Resistance Thermometers.

6. Pyrometers.


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Resistance Temperature Detector (RTD)

Every type of metal has a unique composition and has a different resistance tothe flow of electrical current. This is termed the resistively constant for that

metal. For most metals the change in electrical resistance is directly proportionalto its change in temperature and is linear over a range of temperatures. Thisconstant factor called the temperature coefficient of electrical resistance (shortformed TCR) is the basis of resistance temperature detectors. The RTD canactually be regarded as a high precision wire wound resistor whose resistancevaries with temperature. By measuring the resistance of the metal, itstemperature can be determined. Several different pure metals (such as platinum,nickel and copper) can be used in the manufacture of an RTD. A typical RTD

probe contains a coil of very fine metal wire, allowing for a large resistancechange without a great space requirement. Usually, platinum RTDs are used asprocess temperature monitors because of their accuracy and linearity. To detectthe small variations of resistance of the RTD, a temperature transmitter in theform of a Wheatstone bridge is generally used. The circuit compares the RTDvalue with three known and highly accurate resistors.

RTD using a Wheatstone bridge

Advantages of RTD:

The response time compared to thermocouples is very fast. In the order of fractions of a second.

An RTD will not experience drift problems because it is not self- powered.


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Within its range it is more accurate and has higher sensitivity than athermocouple. In an installation where long leads are required, the RTDdoes not require special extension cable.

Unlike thermocouples, radioactive radiation (beta, gamma and neutrons)has minimal effect on RTDs since the parameter measured is resistance, notvoltage.

Disadvantages:

Because the metal used for a RTD must be in its purest form, they are muchmore expensive than thermocouples.

In general, an RTD is not capable of measuring as wide a temperature rangeas a thermocouple.

A power supply failure can cause erroneous readings

Small changes in resistance are being measured, thus all connections mustbe tight and free of corrosion, which will create errors.

Among the many uses in a nuclear station, RTDs can be found in the reactorarea temperature measurement and fuel channel coolant temperature.

Failure Modes:

An open circuit in the RTD or in the wiring between the RTD and the bridgewill cause a high temperature reading.

Loss of power or a short within the RTD will cause a low temperaturereading.


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Thermocouple (T/C)

A thermocouple consists of two pieces of dissimilar metals with their ends joinedtogether (by twisting, soldering or welding). When heat is applied to the junction,

a voltage, in the range of mili-volts (mV), is generated. A thermocouple istherefore said to be self-powered. Shown in Figure is a completed thermocouplecircuit.

The voltage generated at each junction depends on junctiontemperature. If temperature T1

is higher than T2, then thevoltage generated at Junction 1will be higher than that atJunction 2. In the above circuit,the loop current shown on thegalvanometer depends on therelative magnitude of thevoltages at the two junctions.

Advantages of thermocouples:

Thermocouples are used on most transformers. The hot junction is insidethe transformer oil and the cold junction at the meter mounted on theoutside. With this simple and rugged installation, the meter directly readsthe temperature rise of oil above the ambient temperature of the location.

In general, thermocouples are used exclusively around the turbine hall

because of their rugged construction and low cost.

A thermocouple is capable of measuring a wider temperature range thanan RTD.


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Disadvantages of thermocouples :

If the thermocouple is located some distance away from the measuringdevice, expensive extension grade thermocouple wires or compensating

cables have to be used. Thermocouples are not used in areas where high radiation fields are

present (for example, in the reactor vault). Radioactive radiation (e.g., Betaradiation from neutron activation), will induce a voltage in thethermocouple wires. Since the signal from thermocouple is also a voltage,the induced voltage will cause an error in the temperature transmitteroutput.

Thermocouples are slower in response than RTDs

If the control logic is remotely located and temperature transmitters (milli-volt to milli- amp transducers) are used, a power supply failure will of course cause faulty readings.

Bimetallic Strips

A bimetallic strip is constructed by bonding two metals with different coefficients

of thermal expansion (Figure 10). If heat is applied to one end of the strip, themetal with the higher coefficient of expansion will expand more readily than thelower one. As a result, the whole metallic strip will bend in the direction of themetal with the lower coefficient.


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FINAL CONTROL ELEMENTS

There are many types of final control elements including valves, dampers, feeders,louvers, and variable speed drive devices, although in general the vast majority of

final control elements found in the industrial control world are pneumaticallyactuated valves.

CONTROL VALVE

A valve with actuator that automatically, fully or partially opens or closes the valveto a position dictated by signals transmitted from controlling instruments can becalled as a control valve.

Importance of Control Valve

The actual purpose of the final control element is to regulate the flow of the process fluid strictly in accordance with the dictates of the controller output(PD). In other words the valve must move to a position represented by thevalue of the PD. The faster and more accurately the valve follows thesedictates the better the control variance becomes.

The importance of the final control element cannot be overestimated. Many people mistakenly believe that the valve is not really critical to the control

performance.


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DISTRIBUTED CONTROL SYSTEM

The old system in CPP Plant was single loop controller based, which came inbeginning of year 1984, at the time of Vijaipur-1 project. The system is nowalmost 30 years old and fast moving towards abolescence and non-availablity of spears.

LIMITATIONS OF OLD SYSTEM:-

1. Non-working data acquisition system.

2. Non reliable recording with high maintenance cost.

3. Optimization through cascaded loops not possible.4. Non redundant system.

5. Un-predictive failure due to ageing problem.

WHY WE NEED DCS???

Earlier a conventional split Architecture type SINGLE LOOP CONTROLLER namedas SLPC . The basic process control system for any hazardous chemical/

petrochemical process plant shall have a high rate of reliability and availability asthe loss of control can create an unsafe situation.

WHAT IS DCS???

It is a process control system that uses a network to interconnect sensors,controllers, operator, terminals and actuators . DCS typically contains severalcomputers for controls and uses proprietary interconnections.


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DCS SYSTEM

This system includes both the field area , we also call it as the Hazardous area andthe safe area.

The hazardous area includes the transmitters from which field cables carryingsignals are fed to the junction box where the cables are combined in a simplifiedform so that cables will be arrange in a proper manner.

Then this system is divided in two cabinet system

1. Marshaling cabinet

2. System cabinet

Marshaling cabinet system:-

The field cables are fed to a safety barrier. The barriers supplies +24VDC power tothe field transmitters. The barrier separates the hazardous area and the non-hazardous area. The MTLbarriers are used in CPP plant.

The barrier supplies 24VDC power but receive 4-20mA signal and a digital signalfrom the field transmitters. Then this 4-20mA signal is fed where this signal is

converted into 1-5VDC signal and this signal is transmitted to the input card,which is located at the I/O i.e., END of this cabinet.

System cabinet:-

It consist of analog to digital converter if the signal is in form of analog it convertit to digital or vice versa also. Then this signal is fed to FCS(field control station) orcontroller CS3000 . This cabinet includes different I/O card, power supplies, CPU,communication modules, bus controllers.

All the field instrument like transmitters and control valves are wired to thesecontrollers.

Then there is Operator station where the process of monitoring and operating isdone. Communication bus are used to communicate between controllers and


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operator station and then a ETHERNET cable is used to connect engineeringstation and other supervisory computers.

And at last if needed to convert the current of 4-20mA into pneumatic signal 0.2-

1kg/cm2

. This pneumatic signal helps in operating the control valve, which is afinal control element.

FCS (Field Control Station):

Used to control the process. All the instruments and interlocks created bysoftware reside in the memory of the FCS. All the field instruments liketransmitters and control valves are wired to the FCS.

o Reliable controller

o Cost-effective and capable I/O subsystem

HIS (Human Interface Station)

Used to monitor the process and to operate various instruments.

o The operator station based on Windows XP or Windows2000. (Both areselectable.)

o HIS provides easy & flexible operation .

ENG (Engineering Station)

o Engineering Station is used to do the engineering builder for all thestations like HIS, FCS, CGW etc. ENG is a PC loaded with Engineeringsoftware.

Communication Bus:

Used to communicate between the FCS and the OPS

o V-Net (Communication Bus)

Real-time control bus.

V-NET is a used for communication between HIS, FCS, CGW.

Max 64 Stations can be connected on V-net.


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Transmission speed: 1 GBPS

o ETHERNET (Communication Bus) - it is a standard network in CS3000to connect HIS, ENG and supervisory computers

Transmission speed: 100 MBPS


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PROGRAMMABLE LOGIC CONTROLLERS (PLC)

This training introduces the basic hardware and software components of a

Programmable Controller (PLC). It details the architecture and basic instruction setcommon to all PLCs. Basic programming techniques and logic designs arecovered. This training describes the operating features of the PLC, the advantagesof the PLC over hard-wired control systems, practical applications, troubleshootingand maintenance of PLCs.

INTRODUCTION TO PLCS

Major Components of a Common PLC

PROCESSOR

POWER SUPPLY

I M

N OP DU U T L

E

O M

U O T D P U U L T E

PROGRAMMINGDEVICE

FromSENSORS Pushbuttons

, contacts,

To OUTPUT

Solenoids,contactors,

alarms


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Processor

The processor module contains the PLCs microprocessor, its supporting circuitry,and its memory system.

The main function of the microprocessor is to analyze data coming from fieldsensors through input modules, make decisions based on the users defined control

program and return signal back through output modules to the field devices. Fieldsensors: switches, flow, level, pressure, temp. transmitters, etc. Field outputdevices: motors, valves, solenoids, lamps, or audible devices.

The memory system in the processor module has two parts: a system memory andan application memory.

I/O Module

The I/O interface section of a PLC connects it to external field devices.

The main purpose of the I/O interface is to condition the various signalsreceived from or sent to the external input and output devices.

Input modules converts signals from discrete or analog input devices to logic

levels acceptable to PLCs processor.

Output modules converts signal from the processor to levels capable of driving theconnected discrete or analog output devices.

Advantages of PLCs:-

Less wiring. Wiring between devices and relay contacts are done in the PLC program. Easier and faster to make changes. Trouble shooting aids make programming easier and reduce downtime.

Reliable components make these likely to operate for years before failure.


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PROGRAMMING OF PLC

Power flows through these contacts when they are closed. The normally open(NO) is true when the input or output status bit controlling the contact is 1. Thenormally closed (NC) is true when the input or output status bit controlling thecontact is 0.

AND OPERATION

Each rung or network on a ladder program represents a logic operation. In the rung

above, both inputs A and B must be true (1) in order for the output C to be true(1).

OR OPERATION

In the rung above, it can be seen that either input A or B

is be true (1), or both are true, then the output C is true (1).

Normally Open (NO)

Normally Closed (NC)

Rung B C

Rung

B


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ESD (Emergency Shut Down)

To protect people, environment and equipments safety systems are used thathave to fulfill many more criteria their simply performing safety functions.

Safety:- Safety systems have always confirm to the latest standards such Availability: - If the process is to be cost effective, then they must run

continuously. It is not accepted for them to stop because of error in thesystem.

Cost Saving: - The startup costs combined with reliability maintenance andupgrade costs determine the cost effectiveness of a safety system.

Openness: - The level of networking in automation solutions is growing allthe time. At the same time, there is growing demand to reduce the numbersof different bus system.

Hemant Pathak

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