ei 72logic and dis control

8/13/2019 Ei 72logic and Dis Control

1/15

1.What are the main advantages of PLC?

Modular design High reliability Economy Size Ease of programming Rugged construction and designed to withstand vibrations,temperature,humidity,noise Ability to communicate with computer

2.What are the major areas of application of PLC?

Sequence control,timing,counting,and data calculation Batch or continuous process control Precise position/motion control Open loop or feed back control ,process data acquisition and display

3.Write about the relayWith the relay type,the signal from the PLC output is used to operate a relay and so is able to

switch currents of the order of a few amperes in an external circuit.The relay isolates the PLC

from the external circuit and can be used for both D.C and A.C.switching. Relays are how

ever relatively slow to operate.

4.What are the three sizes of PLCs

Small Medium Large

5.What is the general application of the PLC?PLCs are mostly applied in steel mills,paper and pulp plants,chemical and automotive and

power plants.

6.Write the key factors in selecting a PLC?

The key factor in selecting a PLC is establishing exactly what the unit is supposed to do.In

general it is not advisable to buy a PLC system that is larger than current needs dictate.How

ever,future conditions should be anticipated to ensure that the system is the proper size to fill

the current and possibly future requirements of an application

7.Define memoryMemory is where the control plan or program is held or stored in the controller.The

information stored in the memory relates to how the input and output data should be

processed

8.List the types of memories

Read only memory(ROM) Random Access Memory(RAM) Program Read-Only Memory(PROM) Erasable Programmable Read only Memory(EPROM) Electrically Allocable Read Only Memory(EAROM) Electrically Erasable Programmable Read only Memory(EEPROM)


2/15

Magnetic Core Memory9.Explain the functions of PLC input and Output modules

Input interface modules accept signals from the machine and convert them in tosignals that can be used by the controller

Output interface modules convert controller signals in to external signals used tocontrol machine or process

10.Expalin On delay and OFF delay timerON delay timer:

This increment while it receives power flow and resets to zero when power flow and resets to

zero when power flow is stopped. The On delay timer will turn ON the output device after

delay

OFF delay timer:

OFF delay timer increments while power flow is off and resets to zero when power flow is

on. The Off delay timer will turn OFF the output device after delay.

11.What is a PLC?A programmable logic controllers are industrially hardened micro computers designed to

replace electromechanical relays that perform discrete or continuous functions in a variety of

processing plant and factory environments.

12.Why the term logic is used?

The term logic is used because the programming is primarily concerned with implementing

logic and switching operations

13.Write the operating principle of the logic controllersInput devices and output devices are connected to the PLC. The controller monitors the

inputs and outputs according to the program stored in the PLC by the operator and controls

the machine or process

14.Write about the architecture of PLCIt consists of a CPU,memory,input/output circuitry.The CPU controls and processes all the

operations with the PLC.It is supplied with a clock with a frequency between 1 and 8 MHz.It

also has a bus system,memory and input/output units a system ROM for permanent

storage,RAM for the users program and temporary buffers.

15.What happens when the power supply is switched off?When power supply is lost PLC will loose its programmed content. To prevent the loss of the

programs,when the power supply is switched off,a battery is likely to be used in the PLC to

maintain the RAM contents for a period.

16.Write about the input /output channelsThe input/output channels provide signal conditioning and isolation functions so that sensors

and actuators can be generally directly connected to them without the need for other circuitry.

Common input voltages are 5V and 24V.Common output voltages are 24 V and 240V

17.What are optoisolators

Opto isolators are used with transistor switches to provide isolation between the externalcircuit and the PLC. They are used to provide isolation.


3/15

18.List out the programming languages in PLC

Ladder Logic(LAD) Statement List(STL) Function block diagram(FBD)

19.What is mean by power flow in PLC?

If there is electrical current flow through the relay contacts in a rung,the output relay coil will

be turned ON.This is termed power flow in the ladder rung

20.List the part of PLC

Central processing unit The input/output section Programming device

21.Define program ladderProgram ladders are used to record and store the program or to load pre-programmed

instructions in to the processor.There are two types of program ladders

Magnetic cassette Disk recorder and electromagnetic modules

22.List three possible functions of a PLC programming device

The programming device provides the primary mean by which the user cancommunicate with the circuits of controller.

The programming device allows the user to enter, change, or monitor a PLCcontroller program

23.Explain the function of an optical isolator

There are three main functions Separate the higher ac input voltage from the logic circuits Prevents damage to the processor due to line voltage transients. Helps to reduce the effect of electrical noise, which can pass entire operation of the

processor

24.What is the function of processor in PLC?The processor reads the inputs, executes logic as determined by the application program,

performs calculations, and controls the outputs accordingly. It controls the operating cycle or

processor scan

25.List the relay type instructionsInstruction set is composed of contact symbols so the ladder diagram language is also

referred as contact symbology

26.List three possible functions of a PLC programming device?Easy to use programming equipment is an important feature of the PLC.

The programming device provides the primary mean by which the user

Can communicate with the circuits of controller.


4/15

The programming device allows the user to enter ,change, or monitor a PLC controller

program

27.Explain the function of an optical isolator?There are three main functions . They are

Separatethe higher ac input voltage from the logic circuits.Prevents damage to the processor due to line voltage transients.

Helps top reduce the effect to electrical noise which can pass entire operation of the

processor.

28.List the conditions for drawing the ladder logic ?Contacts may be always inserted in the upper left .

Coils must be inserted at the end of a rung.

All contacts must run horizontally (i.e)no vertically oriented contacts.

The contacts must be nested .

Flow must be from left to right.

Contact progression should be straight across.

29.List the sequence of operations carried out in PLC programming?Processor memory organisation

Program scan

PLC programming language

Relay type instruction

Instruction addressing

Branch instruction

Internal relay instruction

Programming examine ON and OFF instructions

Entering the ladder diagram.

Modes of operation.

30.What is meant by program scan?During each operating cycle the processor reads all the inputs,takes their values and

according to the user program energies or de_energies the output .This process is known as

program scan.

31.What is meant by PLC programming languages?PLC programming languge refers to the method by which the user communicate information

to PLC

32.List the relay type instructions?Instruction set is composed of content symbols so the ladder diagram langue is also referred

as contact symbology

1.EXAMINE ON instructions

2.EXAMINE OFF instruction

3.OUTPUT ENERGISE

33.What is meant by internal relay instructions?Most PLCS have an area of memory allocated for what are known as internal storage bits

.These storage bits are also called internal outputs ,internal coils,internal control relays arejust internals .The internal outputs does not directly control an output device.


5/15

34.List the modes of operations in PLC?There are 5 different modes of operations .They are

1.Connect PLC with PC

2.Clering the Ram

3.Store the logic in the Ram4.Run

5.Continous until stop mode is selected.

35.What are the applications of PLC?1.Sequence control, timing, counting, data calculation

2.Batch (or)continuous process control

3.Pricise position/motion control

4.Open loop or feedback control ,process data acquisition and display

36.What are the word transfer instruction in Allen Bradley PLC5?

Bit distribute(BTD)Move(MOV)

Masked move(MVM)

37.What are the arithmetic operationsADD-addition

SUB-subtraction

MUL-Multiplication

DIV-Division

38.What are the data comparison instructionsEqual to-EQU

Less than-LES

Greater than-GRT

39.Name some program control instruction

Master control relay-MCR

Jump(IMP)

Label-LBL

40.What are the three inputs in PLC sequencer function

Step circuitReset circuit

Enable circuit

41.What are the uses of PCMaximizes plant yields

Increases plant capacity and productivity

Ensures the repeatability an the product quality

Reduces raw material and energy costs

Increases safety of plant operation and improved profitability

42.What are the applications of PCElectric oven temperature control


6/15

Reheat furnace temperature control of mill in an integrated steel plant

Thickness and flatness control system for metal rolling

Automation of hot strip mill in an integrated steel plant

Control of Electric Power Generation plant

43.What are the uses of PLCUsed for logic-based sequencing operations

Used for counting, timing and complex mathematical operations

Used to perform PID, feed forward and other control functions

Large scale PLCs having data highway capabilities function well in DCS environment

44.What is PIDPID stands for Proportional, Integral, Derivative controller. PID is an effective control system

for continuous processes, that performs two control tasks. First PID control keeps the output

at a set level even though varying process parameters may tend to cause the output to vary

from the desired set point. Second, PID promptly and accurately changes the process level

from one set point level to another set point level.

45. What is MCR?The master control relay (MCR) instruction is used in pairs to activate or deactivate the

execution of a group of zone of ladder rungs.

46. What is JMP?

The jump instruction (JMP) allows the normal sequential execution to be altered so the CPU

will jump to a new position in the ladder program.

47. What LBL?The label (LBL) is to identify the Ladder rung that is the destination of a jump instruction.

48. What are the three subroutine instructions?

1.The jump to subroutine (JSR).

2.The Subroutine (SBR)

3.The return (RET)

49. What is EQU?The equal to (EQU) instruction is used to test whether two values are equal.

50. What is LES?Much like the equal to instruction, the less then (LES) instruction tests the contents of the

value of one location (source A) to see if it is less than the value stored in a second location

(source B).

51.Define SCADA?Supervisory Control And Data Acquisition system is computerized hardware and software

based project that provides a single integrated view of all control and information resources,

enable engineers, supervisors, managers, operators to view and interact with the working of

an entire operation through graphical representation of their product process.

5 2.What is CIMPLICITY?

CIMPLICITY is a SCADA package. It is based on a client-server architecture consisting ofservers and viewers. Servers are responsible for the collection and distribution of data.


7/15

Viewers connect into servers and have full access to the collected data for viewing and

control actions.

5 3.State the requirements of CIMPLICITY HMI plant edition?

CIMPLICITY HMI Plant Edition provides an extraordinary selection of features that enables

to configure comprehensive and robust project. It gives a quick tour which provides links tothe related subject in the documentation.

5 4. What is a DDC?

The DDC (Direct Digital Control) directly interface to the process for data acquisition and

control purposes.

55. List the tasks performed by microprocessor in DDC?

It reads the various variables from different transmitters through multiplexer and ADC.

It determines the error for each control loop and executes control strategy for each loop.

It outputs the correction value of control valve through DAC.

56.Mention the two algorithm used in DDC software?There are two algorithms for programming a three mode PID control loop

Position algorithm

Velocity algorithm

5 7.Define AI?

Artificial Intelligence has been defined as the branch of computer science which deals with

the software and hardware techniques to solve symbolic problems as against number

crunching problems solved by EDP machines.

58.What is heuristics?The learned facts, experience and institution are three basic inputs which enable decision

making collectively these are known as heuristics. In AI systems the decisions are taken on

the basis of heuristics.

59.Mention the various categories under the AI system.Natural language system

Perception system

Expert or knowledge based system

60.List the various types of information presented to expert system.The information presented to the expert system may be factual, incomplete, judgmental,

speculative, experimental, uncertain, fuzzy and intuitive. Expert system should derive

conclusions based on such incomplete information just like real life human expert.

61.What is domain knowledge?The domain knowledge is stored in the knowledge base of system. The domain knowledge

contains:

Facts

Relation between facts

Heuristics

62.Differentiate the two reasoning mechanics.


8/15

Backward chaining:-stars with a goal i.e. conclusion which is most portable and then tries to

go backward and match the left hand side of rule i.e. conditions.

Forward chaining:-is a top down approach. It proceeds in the direction until the goal i.e.

conclusion is reached.

63.List the goals for an ideal expert controller. Ability to control a large class of processes which may be time varying, non linear,

with variety of disturbance.

Requirement of minimum prior knowledge about the process. Ability to improve itsperformance with time, as it acquires more knowledge.

64.Differentiate between analog controller and digital controller.

Analog controller though are faster than digital controllers, the later is preferred because the

changes in the parameters values are possible in digital controller while not in analog

controller.

65.List down the methodologies used in knowledge representationIt includes

Sematic networksIn this,nods and arcs form graphical notation to represent objects and relationship among

them

FramesFrames are templates or modules for holding clusters of related knowledge about a particular

narrow subjects

RulesRules may be in one of the three forms

a)If {this happens} then do {that} or

b)If(this is the case} then {that is true} or

c) If { this is the case} then do {that}

66.What are the operational objectives that a control system is called upon to achieve?

Ensuring the stability of the process Supporting the influence of external Optuimising the economic performance of a plant or A combination of the above

67.What are the main constituents of the fuzzy controller Fuzzifier Knowledge base Decision strategy Defuzzifier

68.What are the advantages of neural network?

Good fit for non linear models Ability to adapt,generalize and extrapolate results Speed of execution in recall mode Ease of maintenance


9/15

69.What are the disadvantages of neural networks?

Cannot handle constraints Cannot optimize Needs of lots of data Needs lots of CPU power in training session Are unpredictable for utilization in untrained areas

70.What is the important concept in fuzzy logicIt is the grade of membership-A number which describes the extent to which an element is in

a set.It also describes the truth value of a particular statement.

71.What is meant by membership function?The grade of membership of fuzzy set is defined by membership function.The membership

function provides a direct linkage between fuzzylogic and fuzzy sets.It is defined by

mA(x).Where x is a member of A and A is some proportional or predicate class.

72.What is fuzzy controller?A controller which is used to control the complex processes is to investigate the control

stratergies followed by a human operator which are based on institution and experience.

73.What is mean by fuzzificationIn fuzzy controller,in order to include the control statergy of human operator the ensor

readings which are non-fuzzy should be converted to fuzzy from by a process called

fuzzification

74.What are the manipulated variables to be used to control the process

Ususally in a process, there are number of inputs,variables adjusted freely.Which one weselect to use as a manipulated variables is a crucial question,as the choice will affect the

quality of control actions

75.What are the measure problems in velocity algorithm?

Controller drift Integral overshoot

76 What is the significance of DCS?Used for interfacing and computing functions and also provides the means of

communication between the other devices. It consists of local control unit, low level

interface, high level interface, shared communication facility. Etc

77. Mention any two advantages of DCSmore reliable

small expensive

cost is lower than centralized system which performs the same function.

78. What is LCU?Local control unit is the small collection of hard ware in the system that can do closed

loop control. Local control unit interfaces directly to the process.

79. What is the significance of LLHI?


10/15

This is the device that allows the operator or instrumentation engineer to interact with

the LCU to change set point, control modes, control configuration, or tuning using a direct

connection. LLHI can also interface directly to the process.

80. What is the function of HLOI?

It has the functions similar to the LLHI with increased capacity and user withincreased capability and user friendliness. It interfaces to other devices only over the shared

communication facilities. Operator oriented program at this level is called HLOI. It is an

instrument engineer oriented program.

81. What is shared communication?One or more communication hardware and associated software that allow the sharing

of data among all devices in the distributed system. Shared communication facilities do not

include dedicated communication channels between specific devices.

82. What is the need can be satisfied in designing an industrial grade LCU?

flexibility of changing the control configurationAbility to use the controller without being a computer expert.

Ability to by pass the controller in case it fails. So that the process still can be

controlled manually.

Ability of the LCU to communicate with other LCUs and other elements in system.

83. What is the architecture parameter to be considered while selecting LCU?

size of controller

functionality of controller

performance of controller

communication channels out of controller

Controller output security.

84. Compare the configuration of the controller

85. What are the security requirements of LCU?

Maximize the availability of the automatic control functions of the system.

Architecture

parameter

Configuration A Configuration B Configuration C

Controller size Number of function

needed for single

PID loop or motor

controller

Includes functions

and I/O

Equivalent to small

DDC system

Controllerfunctionality Uses both continuesand logic function Uses both continuesand logic function

Split between the

controller

Uses both continuesand logic function

Controller scalability High degree of

scalability

Requires both

controller types

Not scalability


11/15

During failure of the controller allows the operator to take the manual control of that

process?

Operator can shut the process down in an orderly and safe manner.

86. Write objectives of DCS.

1. Safe operation of plant2. Lowest cost of operation

3. Longest equipment life

4. Minimum environment effect

5. Maximum efficiency

87. What is distributed system?A distributed system is one in which components located at networked computers

communicate and coordinate their actions only by passing messages.

88. What is DCS?

A distributed control system (DCS) refers to a control system usually of amanufacturing system, process or any kind of dynamic system, in which the controller

elements are not central in location (like the brain) but are distributed throughout the system

with each component sub-system controlled by one or more controllers. The entire system of

controllers is connected by networks for communication and monitoring.

89. Write benefits of DCS?High reliabilityreduce human error

Improved response time

allowing easier identification of bottle-necks

Improve operator interface to plant

better production scheduling, making maximum use of the production

facilities

Improve accessibility of plant data to engineering & management personals

- Faster identification of faults in both product and processing machinery

Historical storage & retrieval system.

90. Write DCS elements1.

Local Control Unit: This unit can handle 8 to 16 individual PID loops.

Data Acquisition Unit: Digital (discrete) and analog I/O can be handle.

Batch Sequencing Unit: This unit controls a timing counters, arbitrary functiongenerators, and internal logic.

Local Display: This device provides analog display stations, and video display for

readout.

Bulk Memory Unit:This unit is used to store and recall process data.

91. Write DCS elements2.

General Purpose Computer:This unit is programmed by a customer or third party

to perform optimization, advance control, expert system, etc

Central Operator Display: This unit typically contains several consoles for operator

communication with the system, and multiple video color graphics display units


12/15

Data Highway: A serial digital data transmission link connecting all other

components in the system. It allow for redundant data highway to reduce the risk of

data loss

Local area Network(LAN

92. What are the Advantages of DCS? Access a large amount of current information from the data highway. Monitoring trends of past process conditions. Readily install new on-line measurements together with local computers. Alternate quickly among standard control strategies and readjust controller

parameters in software.

A sight full engineer can use the flexibility of the framework to implement hislatest controller design ideas on the host computer.

93. List the Modes of Computer control.1. Manual2. Automatic

PID with local set point3. Supervisory

PID with remote set point (supervisory)4. Advanced

94. What are the two methods that control the flow of data across communication links?

1) Stop and wait 2) sliding window

95. What is the mechanism of stop-and-wait flow control?In the stop and wait method of flow control sender sends one frame and waits for an

acknowledgement before sending the next frame.

96. What is the mechanism of sliding window flow control?

In the sliding window flow control; the sending of data is constrained by imaginary

window that expands and contracts according to the acknowledgement received by the

sender.

97. What does the term error control mean in the data link layer?Error control in the data link layer is based on the automatic repeat request which

means retransmission of data in three cases: damaged frame lost frame, lost acknowledgment.

98. What is the mechanism of poll/select?A poll is sent to the secondary device by the primary to determine if the secondary has

to send. The secondary can respond by sending a acknowledgement or a data frame. A select

frame is sent from the primary device to the secondary device to tell the secondary to prepare

to receive data. The secondary responds with an ACK or a NAK

99. Define protocol.A protocol in data communications is the set of rules or specifications used to

implement one or more layers of the OSI model.

100. What are the two types of data link protocol?1).Asynchronous protocol 2).Synchronous protocol


13/15

101. What is manual backup?In this case, each LCU is designed to implemented only one or two control loops , and

reliable is placed on the operator to take over manual control in case of a failure of LCU.

10 2. What is redundant control mode?

In this case, the LCU is backed up by another LCU that takes over if the primarycontroller fails. In this way, full automatic control is maintained even under failure

conditions.

103. What are the approaches in designing a redundant LCU architecture?a) CPU redundancy,

b) One-on-one redundancy,

c) One-on-many redundancy,

d) Multiple active redundancy.

104. What is meant by geographically centralized and geographically distributed

control system?All the LCUs are located in a central equipment room area; it is called as

geographically centralized control system. Each LCU is located in the plant area closest to

the portion of the process that it controls. It is called as geographically distributed control

system.

105. What is functionally distributed control system?

Several LCUs are used to implement the functions required in controlling the

process. Therefore it is called as functionally distributed control system.

106. What are multiple active controllers?In this case, several LCUs are active at the same time in reading process inputs

calculating control algorithms and producing control outputs to the process. The multiple

active approaches is designed so that a failure of one of the controllers does affect the

automatic control function.

107. What are the redundant approaches of redundant controllers?The redundant architecture should be kept as simple as possible. There is a law of

diminishing in redundancy design. At some point, adding more hardware will reduce system

reliability. The redundant nature of the controller configuration should be transparent to the

user that is the user should be able to deal with the system in the way as a non redundant one.

108. Mention the requirement of operator interfaceprocess monitoring

process control

process record keeping

109. What are the motivations for using LLOI?It provides an interface that is familiar to the operator trying to use panel board

instrumentation.

Less expensive

Provide manual back up in the case if high level operator interface fails.

110. Explain about different types of operator display.


14/15

Plant display.

Area display.

Group display.

Lop display.

Graphic display.

Trend display.Tabular display.

111. What is the function of engineering interface?

system configuration

operator configuration

system documentation

system failure diagnosis

112. What is data transparency?Data transparency in data communication means we should be able to send any

combination of bits as data. The combination of bits as data is not confused with the controlinformation.

113. Define BSC.Binary synchronous communication is a well-known character oriented protocol

.BSC operates in half-duplex mode using stop and wait ARQ in a point to point or

multipoint configuration.

114. What is bit stuffing?

Bit stuffing is the process of adding one extra 0 whenever there are five

consecutive 1s in the data. So that the receiver doesnt mistake the data for a flag.

115. What do you mean by HDLC?High-level data link control is a bit oriented data link designed to support both half-

duplex and full-duplex communication over point-to point and multi point links.

116. How do the three HDLC frame types differ from one another?a)I-frame -for data transmission and control

b)S-frame-control

c)U-framefor control and management

117. What are the types of modes in HDLC?a) Normal response mode (NRM)

b) Asynchronous response mode (ARM)

c) Asynchronous balanced mode (ABM)

118. What is piggy bagging?Piggy backing means combining data to be sent and acknowledgement of the frame

received in one single frame.

119. Name the four types of s-frames?

a) Receive ready(RR)b) Receive not ready (RNR)


15/15

c) Reject (REJ)

d) Selective reject (SREJ)

120. Name the five categories of U-frame.1) Mode setting

2) Unnumbered exchanging3) Disconnection

4) Initiation

5) Miscellaneous

1 21. What are the types of sliding window ARQ error control?1) go-back-n 2) Selectivereject

122.Distinguish X-modem and Y-modem?

X-modem Y-modem

1.the data is 128bytes

2one CANS signal is used to abort a

transmission

3.CRC error checking is used

4.It is a half-duplex stop and wait ARQ

protocol

1.the data unit is 1024bytes

2.two CAN signals are used

3.ITU-T CRC is used for error checking

4.here multiple files can be sent

simultaneously

123. What are the disadvantages of asynchronous transmission?1).speed of transmission is less

2)It leaves unpredictable gaps of time between each character

3).the addition of start and stop bits and the insertion of gaps into the bit stream make

asynchronous transmission slower.

124. What are the two types of synchronous protocol and explain it?

1) Character oriented protocol

2) bit-oriented protocol

125. What is routing table?A routing table has columns for at least three types of information: the network ID

and ID of the next router. The network ID is the final destination of the packet. The cost isthe number of hops a packet must make packet to get there. And the next router is the router

is the router to which a packet must be delivered on its way to a particular destination.

ei 72logic and dis control

Documents