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DCS Distributed Control System Interview Questions 2 contains Elements Of Distributed Control System, Open Loop Control System,  Closed Loop Control System,  PLC, Ground Loop, Globe Type Control Valve, Flow, Control Loop.

14. What Are The Basic Elements Of Distributed Control System?
15. Explain Open Loop Control System?
16. What Are The Advantages And Disadvantages Of Open Loop Control System?
17. Explain Closed Loop Control System?
18. What Are The Advantages And Disadvantages Of Closed Loop Control System?
19. What Is The Significance Of Single Ended & Differential Ended Input For PLC? What is Application Wise Comparison of These Two Types of Inputs?
20. What Is Ground Loop? What are Preventive Steps to Avoid Ground Loop?
21. In a Globe Type Control Valve, What Is the Importance of Flow Direction (top To Bottom or Bottom to Top)?
22. How Control Loop Should Be Tuned In Process Loop?

14. What Are The Basic Elements Of Distributed Control System?

Basic Elements of Distributed Control System :

Distributed Control System continuously interacts with the processes in process control applications ones it gets instruction from the operator. 

It also facilitates to variable set points and opening and closing of valves for manual control by the operator. Its human machine interface (HMI), face plates and trend display gives the effective monitoring of industrial processes.

15. Explain Open Loop Control System ?

Control System in which output quantity has no effect on the input quantity is called Open Loop Control System. 

Open Loop Control System has no facility to correct automatically the error generated in the output. From output of the system no feedback is given back to the input for correction. 

In Open loop control system the output can be varied by varying the input. But due the external disturbance system output may change. 

Any variation in the output from the desired once again attained by varying the inputs manually.

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

Advantages

  • Open loop system is simple and economical.
  • Construction of open loop system is easier.
  • Open loop systems are generally stable.

Disadvantages

  • Open loop systems are inaccurate and unreliable
  • The changes in the outputs due to external disturbance are not corrected automatically

17. Explain Closed Loop Control System ?

Control system in which the output has an effect on the input quantity in such a manner that the input quantity will adjust itself based on the output generated is called Closed loop Control System. 

Open loop control system can be modified in to closed loop control system by providing a feedback.

 This feedback automatically corrects the changes in the output due to external disturbance. Hence closed loop control system is called automatic control system.

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

Advantages:

  • Closed loop control systems are more accurate even in the presence of non-linearity
  • The sensitivity of the system may be made small to make the system more stable
  • The closed loop systems are less affected by noise.

Disadvantages:

  • Closed loop control systems are costlier and complex
  • The feedback in the closed loop system may lead to oscillatory response
  • The feedback reduces the overall gain of the system
  • Stability is the major problem in the closed loop system and more care is needed to design a stable closed loop system.

19. What Is The Significance Of Single Ended & Differential Ended Input For Plc? Application Wise Comparison Of These Two Types Of Inputs?

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

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

When ground wiring is not done properly, grounding of various points is not effective and potential differences exist between them resulting in currents flowing between them. 

This leads to  measurement errors and is not desirable. It can be eliminated by proper ground wiring.

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

Control valves must be installed as per direction marking provided by the manufacturers or instruction manuals. Though people tend to generalize, this is often misleading.

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

You may use Ziegler-Nichol’s method ( open loop / closed loop ) or special tuning software tools.

Thanks for reading - DCS Distributed Control System Interview Questions 2
Naitik Patel
Industrial Guide

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