Interview Questions.

Question 1. What Is A Distributed Control System ?

Answer :

A disbursed manage system (DCS) is a computerised manipulate machine for a method or plant, in which self sufficient controllers are dispensed for the duration of the gadget, however there may be vital operator supervisory control.

Question 2. In Split Range Control, Whether The Signal Is Splitted Through I/p Converter Or The Converter Itself?

Answer :

This may be typically completed with the aid of  approaches:

By connecting o/p of 1 I/P converter to 2 positioners adjusted definitely for break up variety operation of manage valves.

Taking  AO from DCS. Split range to be defined in DCS. Both I/P converters and positioners to be calibrated with enter as 4to20 ma dc and 3to15 psi respectively.

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Question three. What If Thermocouple Wire Is Opened In The Field? What Signal Goes To Dcs?

Answer :In most present day units the sign can be programmed to go to either most or minimal depending upon give up user’s requirement.

Question 4. What If The Power Supply Connections To A Two-wire Transmitter Get Interchanged? What Signal Will Go To Dcs?

Answer :Usually there may be a blockading diode to shield the transmitter against supply reversal and nearly 0 contemporary sign should be transmitted.

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Question five. What Is The Difference Between A Hart Patch Card And A Field Terminal Assembly?

Answer :A area terminal assembly is a DCS factor where discipline alerts are terminated. In a DCS using analog transmitter alerts however smart remotely configured transmitters discipline alerts from boundaries are first delivered to a HART patch panel. From right here the analog indicators are stressed to the DCS area termination assembly or I/O card. The digital indicators are wired to the HART multiplexes who extract the digital records and offer two way communique direction among smart contraptions and a laptop walking suitable software.

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Question 6. What Is The Difference Between Dcs And Plc?

Answer :

Distributed manage device(DCS) and Programmable common sense controller. These are the manipulate systems which handles fields I/Os. Basic difference between DCS & PLC is

DCS handles extra nos of I/Os as opposed to PLC.
 PLC is faster device than DCS.
 DCS can handles handsome quantity of I/Os in order that can be used for total plant automation. Where as PLC has very own boundaries so it normally used for small however for vital(Safety factor of view) devices, like boiler automations, Make-up compressor automations Etc.
 In the above stated case the those PLC’s may be get related with the DCS with the help of gentle link. Generally this is used to make alert to both the operator.
 As I heard the PLC used to deal with the DI/DO signals so it can take rapid movements. Some of the time it is used to handle few nos of AI/AO.
 DCS & PLC’s speed relies upon on the test charge of I/Os.
For each the device Marshalling panels, Consoles and different schools of Ethernet Etc may be used consistent with the want.
According to the Cause and results diagrams the System programmer assigns the control action block into the device, we are able to call them as memory assigning.
Question 7. When Proportional, Integral And Derivative (pid) Controller Is Used?

Answer :

PID controller is used while device calls for:

System adjustments are small.
Offset ought to be removed.
Fast recovery time.
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Question 8. When Proportional (p) Controller Is Used ?

Answer :

Proportional (P) Controller is used throughout the following situations:

Load Changes are small.
Offset (errors exist because of difference among regular kingdom price and favored cost) can be tolerated.
The system response rate is which includes to allow a slim proportional band. Since this reduces the quantity of the offset.
Question nine. When Proportional (p) Controller Is Used ?

Answer :

Proportional (P) Controller is used all through the subsequent conditions:

Load Changes are small.
Offset (error exist due to distinction between regular kingdom price and desired value) can be tolerated.
The system reaction rate is which include to permit a slim proportional band. Since this reduces the quantity of the offset.
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Question 10. When Integral (i) Controller Is Used ?

Answer :

Integral (I) controller is used for the duration of:

When the offset need to be eliminated.
Integral saturation because of sustained deviation isn't objectionable.
Question eleven. When Derivative (d) Controller Is Used ?

Answer :

Large transfer or distance velocity lags are gift.
It is important to minimize the quantity of deviation because of the gadget changes.
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Question 12. When Proportional Plus Integral (pi) Controller Is Used

Answer :

Proportional and Integral movement is employed while

System adjustments is small.
Offset have to be eliminated.
No objection at the recuperation period.
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Question thirteen. When Proportional And Derivative (pd) Controller Is Used ?

Answer :

PD action is employed when:

When the machine adjustments are small.
Improve the healing time.
When system lags are high.
Question 14. What Are The Basic Elements Of Distributed Control System?

Answer :

Basic Elements of Distributed Control System :

Distributed Control System constantly interacts with the approaches in process manipulate packages ones it gets practise from the operator. It also allows to variable set points and starting and ultimate of valves for guide manage with the aid of the operator. Its human system interface (HMI), face plates and fashion show gives the effective monitoring of industrial processes.

Question 15. Explain Open Loop Control System ?

Answer :

Control System in which output amount has no impact at the input quantity is called Open Loop Control System. Open Loop Control System has no facility to correct automatically the error generated inside the output. From output of the gadget no feedback is given returned to the enter for correction. In Open loop manipulate device the output may be varied via various the enter. But due the external disturbance system output may change. Any version within the output from the preferred once more attained through varying the inputs manually.

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Question sixteen. What Are The Advantages And Disadvantages Of Open Loop Control System ?

Answer :

Advantages:

Open loop system is straightforward and inexpensive.
Construction of open loop device is less difficult.
Open loop systems are normally stable.
Disadvantages:

Open loop structures are inaccurate and unreliable
The adjustments inside the outputs due to external disturbance are not corrected automatically
Question 17. Explain Closed Loop Control System ?

Answer :

Control machine wherein the output has an impact on the input amount in this type of manner that the input amount will alter itself based totally on the output generated is called Closed loop Control System. Open loop manage machine may be changed in to closed loop manage device through presenting a remarks. This remarks routinely corrects the adjustments in the output because of outside disturbance. Hence closed loop control gadget is called automatic manage system.

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Question 18. What Are The Advantages And Disadvantages Of Closed Loop Control System ?

Answer :

Advantages:

Closed loop manipulate structures are greater correct even within the presence of non-linearities
The sensitivity of the system may be made small to make the gadget extra strong
The closed loop systems are less suffering from noise.
Disadvantages:

Closed loop manage structures are more expensive and complex
The remarks inside the closed loop system might also result in oscillatory response
The remarks reduces the overall advantage of the machine
Stability is the essential problem inside the closed loop system and more care is needed to layout a solid closed loop machine.
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Question 19. What Is The Significance Of Single Ended & Differential Ended Input For Plc? Application Wise Comparison Of These Two Types Of Inputs?

Answer :

Differential inputs provide better commonplace mode rejection and signal-to-noise ratio.

Question 20. What Is Ground Loop? Preventive Steps To Avoid Ground Loop?

Answer :

When ground wiring isn't always completed well, grounding of diverse points isn't always powerful and capacity variations exist between them resulting in currents flowing between them. This results in dimension mistakes and isn't proper. It may be eliminated by means of right floor wiring.

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Question 21. In A Globe Type Control Valve, What Is The Importance Of Flow Direction (top To Bottom Or Bottom To Top)?

Answer :

Control valves should be established as according to route marking furnished via the producers or education manuals. Though human beings have a tendency to generalize, this is regularly deceptive.

Question 22. How Control Loop Should Be Tuned In Process Loop?

Answer :

You may additionally use Ziegler-Nichol’s method ( open loop / closed loop ) or unique tuning software program gear.