Instrumentation Questions

300+ Instrumentation Engineering Interview Questions – Part 6

1. What is the purpose of an inclined manometer?

It is used to increase the instrument’s scale. Because the manometer is angled with respect to the vertical.

2. What is the output range of transmitter?

4 -20 ma or 0-10 V

3. What is the drift?

Changes that occurred in the instrument calibration are called drift. Drift is the term used to describe how an instrument’s calibration shifts over time.

4. Define positioning action?

This is the action in which there is a predetermined relationship between the value of the controlled variable and the position of the final control element.

5. Define proportional action?

The existence of a continuous linear relationship between the value of the actual measurement of the controlled variable and the value position.

6. What is sensitivity?

The instrument reacts to even the smallest variation in the measured variable.

7. Stroboscope is used for the measurement of____?

Angular velocity

8. Which materials do not have a covalent bond?


9. What is the constant voltage circuit?

This is the power circuit that is utilised to keep the output consistent.

10. What is an embedded system?

A Microcontroller-based system that is tailored to perform certain task.

11. What is the other name of Multiplexer?

Multiplexer: Data selector

12. What is the other name of De-Multiplexer?

De-Multiplexer: Data Distributer

13. What is an opto-coupler?

It is a semiconductor device that transmits an electrical signal between two isolated circuits.

14. What is the another name of opto-coupler


15. What are the benefits of an opto-coupler?

1). One-way signal transmission

2). Total electrical isolation between the input and output

3). Can be used to separate a low voltage circuit from a high voltage circuit.

16. Disadvantages of Opto-coupler?

1). Optocouplers cannot handle high currents.

2). For operation, an optocoupler requires an external biasing voltage.

3). The high-frequency response is inadequate.

4). Phototransistor-based optocouplers do not have the same linear relationship between changes in light input and output current as photodiode-based types.

17. Name the applications of opto-coupler?

1).Used to isolate the ground.

2). Typically found in high voltage monitoring circuits.

3). Typically found in lighting control circuits.

4). In dimmer circuits.

18. Define Modbus?

A protocol for electronic device communication is called Modbus. Given that the protocol is open source, anyone can use it to enable communication between their electronic gadgets. Over serial lines, electronic gadgets talk to one another.

19. Define Profibus?

The Profibus is a standard for communication in the fieldbus domain, which is the name of a family of industrial computer network protocols. It is also referred to as the Process Field Bus. The automation industry makes considerable use of the Profibus.

20. Define Fieldbus?

A family of protocols used specifically for computer networks goes by the name of “Fieldbus.” A distributed control system and a structured hierarchy of controller systems are required for complex automation systems in industry, such as the manufacturing assembly line, to function properly.

21. Define live zero?

The term “live zero” refers to a loop signal in which the zero value is greater than zero (i.e. 4 mA) .

22. Define dead zero?

The term dead zero refers to a loop signal in which the zero value is, in fact, zero (i.e. 0 mA).

23. CNC Stands for

Computerized Numerical Control

24. The Active transducer also known as?

Self-generating type of transducers.

25. Which transducer converts heat energy into electrical energy?


26. Which phenomenon depends on Avalanche breakdown?


27. In temperature records, how is automatic reference junction compensation performed?

Variable nickel resistors are used in automatic reference junctions. Temperature changes cause resistance to change. The reference junction compensator is positioned so that it is at the reference junction’s temperature. The reference junction is located at the point where the thermocouple’s dissimilar wire is re-joined. This joint is invariably located at the instrument’s terminal strip.

28. Which phenomenon depends on Zener diode?

High-intensity electric field

29. Advantages of CNC

1). Can use continuously

2). Consistency, Precision and Redundancy

3). Low Skill Requirement

4). Flexibility

5). Capability

30. Explain DI?

DI stands for Digital Input. Digital inputs are binary inputs (0 or 1) used by the PLC. Binary inputs are voltages that range from 5V to 230V depending on the type of card used. Simply put, any pushbutton, switch, or sensor generates digital inputs to a PLC. Digital inputs are used to determine whether a device is turned on or off. For a 24Vdc input module, 0Vdc is the OFF state (Binary 0), and 24Vdc is the ON state.

31. Explain DO?

DO stands for Digital Output. PLC digital outputs are binary outputs (0 or 1) It is a field-processed control output from the PLC. It is used to turn any piece of field equipment ON or OFF. DO functions similarly to a relay contact in that when the pre programmed conditions are met, the contacts close. DO can be used to control solenoid valves, relays, indicating lamps, or any other device.

32. What is AI?

Analog input is a continuous field input to the PLC. Is not a constant voltage signal, unlike digital signals. It varies according to the field conditions. The most commonly used analogue signals are 4-20mA and 0-10Vdc. The input signal can range between 4-20mA and 0-10Vdc depending on the field conditions. For example, if you use a pressure transmitter with a range of 0-10 Bar to monitor the pressure of water flowing through a pipe, the transmitter will output a signal between 0 and 10V proportional to the pressure in the pipe.

33. What is AO?

The analogue output is a continuous signal from the PLC to the field devices. You can use analogue output to provide a speed reference signal to a variable frequency drive, for example. Otherwise, if you are measuring the pressure with analogue input as described above and want to display it on an analogue meter, you can use a PLC’s analogue output.

34. Difference between DI and AI?

Data collected from the field is represented by digital and analogue input. Digital input is binary in nature, meaning it can only be ON or OFF. Depending on the type of IO module used, it can be either 0V or 24V. Digital input devices include switches, sensors, and so on. A time-varying signal is an analogue signal. Depending on the design, it can range from 0-10V to 0-20mA. Analogue input devices include transducers.

35. Difference between DO and AO

A digital output is binary in nature, meaning it can be either ON or OFF. Depending on the type of IO module used, it can be either 0V or 24V. A time-varying signal is an analogue signal. Depending on the design, it can range from 0-10V to 0-20mA.

 36. Purpose of Pirani gauge

Low-pressure measurement

37. Psi stands for

Pounds per square inch

38. Low pressure expressed in


39. What is UPS?

When the primary power source fails, an uninterruptible power supply (UPS) keeps the system running for at least a short time. UPS equipment also protects against power surges.

40. What is an inverter?

It is the electrical equipment used to convert D.C power from the battery into A.C power.Because a battery saves electricity as D.C, we need an inverter to convert it to A.C because most equipment is designed to operate on A.C power.

41. What are non-slam check valves?

Swing check valve, conventional check valve, wafer check valve, tilting disc check valve, piston check valve, stop checkvalve, ball check valve.

42. What kinds of material being used for impulse tubing pressure leak testing?

Nitrogen and water

43. Types of bourdon valves

1). C Type

2). Helix

3). Spiral

44. What is a CNC Machine?

A CNC machine is an automated machining system controlled by a computer that executes pre-programmed sequences of control commands. CNC machines replace traditional machines that were manually controlled by levers, handwheels, or mechanically automated using cam systems with integrated software.

45. Components of a CNC Machine

1). Software

2). Machine Control Unit (MCU)

3). Processing Equipment.

46. List different test inputs

Test inputs come in a variety of forms, including

  1. Step,
  2. Ramp,
  3. Impulse,
  4. Sine, and
  5. Pulse.

47. How would define self-regulation?

Self-regulation is the process through which an input undergoes a persistent change while the output alternates between two steady states. The output variable will increase in response to changes in some input variables until it achieves a steady state where inflow equals outflow. Through this technology, the process adopts a certain controlled variable value for nominal load without requiring any control activities.

48. What two characteristics does a first order process modelling show?

The initial response of the system would be steeper the smaller the time constant’s value. For a unit step change in the input, a first order lag process self-regulates with an ultimate value of the response equal to Kp or steady state gain.

49. Why is the electronic controller recommended over the pneumatic controller?

Electronic vs. Pneumatic Controls: Fundamentally, electrical signals function instantly over long distances. Digital controllers can be developed to work with these electronic signals. As electrical risks are eliminated by intrinsic safety measures, electronic equipment can be made to require essentially no maintenance. Additionally, they require less money to install and use less energy. Electronic controllers are chosen over pneumatic controllers because of these beneficial features and characteristics.

50. What is Bernoulli’s Theorem and where is it applicable?

Bernoulli’s theorem states the “Total energy of a liquid flowing from one point to another remains constant.”It works with non-compressible liquids.

300+ Instrumentation Engineering Interview Questions – Part 1

300+ Instrumentation Engineering Interview Questions – Part 2

300+ Instrumentation Engineering Interview Questions – Part 3

300+ Instrumentation Engineering Interview Questions – Part 4

300+ Instrumentation Engineering Interview Questions – Part 5

Rabert T

As an electrical engineer with 5 years of experience, I focus on transformer and circuit breaker reliability in 110/33-11kV and 33/11kV substations. I am a professional electrical engineer with experience in transformer service and maintenance. I understand electrical principles and have expertise troubleshooting, repairing, and maintaining transformers, circuit breakers, and testing them. Tweet me @Rabert_infohe

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