Interview Questions

50+ Industrial automation interview questions

1.What are the major functions of a supervisory control system?

A. There are three major functions for a supervisory control systems and they are

Set point generation

Process monitoring

Operator interface

2.Explain automation ?

A. Automation is a process that can reduce human efforts, we can see the use of automation in many industrial applications. The machines in a factory can be controlled by using automation.

3.What are the functions of a production control system?

A. The product control system does the scheduling of the process, and it also does the inventory and maintenance management.

4.What are the types of control systems that is used in automation?

A. In automation, there are different kinds of the control system and they are

PLC control system

DCS control system

PID control system

PC based automation system

5. What are the major components that is required for automation?

A. There are many components in an automation system like sensors, transmitters, control systems, and output devices. The sensors are used to sense the input, and transmitters are used to transmit electrical signal. The control system is composed of PLC, DCS etc. The actuators and control valves are the output devices.

6.How is a PLC different from relay?

A. A relay cannot be programmed but the PLC can be programmed, relay is not advanced like PLC. PLC can work with analog I/O’s whereas the relay cannot do this.

7.What is the difference between a DCS system, a SCADA system, and a PLC system??

A. Distributed control system (DCS) is a computerized system used to control industrial processes that span a large geographical area.

SCADA (supervisory control and data acquisition) system is a computerized monitoring and controlling system for industrial processes.

Programmable logic controller (PLC) is a computer system used to manage repetitive industrial processes.

8.What knowledge do you have of serial communication protocols??

A. To transmit data between devices, serial communication protocols are utilized. The most used serial communication protocol is RS-232, which is utilized to link computers and peripherals.RS-485 and RS-422 are two other serial communication standards.

9. Could you please explain what HMI stands for? What is its function?

A. HMI is the abbreviation for Human Machine Interface. HMIs are designed to facilitate human interaction with machines, especially industrial machinery, by providing a graphical user interface. This might range from a basic display of information to a more complicated interface that enables the machine’s control.

10. What exactly is meant by the term “Internet of Things”? What does this have to do with industrial automation??

A. The Internet of Things, sometimes known as IoT, is a network of physical devices that are linked to the internet and can exchange data. This information can be utilized to automate a variety of operations, including those seen in industrial settings. For example, if a machine in a plant is connected to the Internet of Things, it can communicate data about its performance and maintenance requirements with other machines and human operators. This data can then be used to improve the overall efficiency of the factory.

11. In PLC, what does scan mean??

A. Any sequential program controller activity is referred to as SCAN. The process generates all updated outputs that match the given inputs.

The ladder diagram shows the SCAN process in action. It takes a total of one cycle to read the input, run the program logic, and update the matching output.

12. What are the different types of sensors used in automation?

A. There are many types of sensors used in automation they are temperature sensors, pressure sensors, flow sensors, and there are sensors to detect the level, conductivity, and density.

13. Why do we 4-20mA signal instead of 0-10V?

A. The 4-20mA signal has the advantage that it won’t drop signal value during long-distance travel, but in the case of the 0-10V, it is different the signal will drop due to the line resistance.

14. What is the use of capacitive sensors?

A. It can sense metallic and non-metallic objects

15. What is the use of inductive sensors?

A. Inductive sensors can sense metallic body without touching it

16. What is industrial automation?

A. We can see most of the industries uses automation and it is used to reduce manpower. Many manufacturing industries have replaced manpower with automation nowadays we can see automated machines, automated monitoring systems. So most of the industrial machines are automated and they also have automated control systems.

17. What are the benefits of industrial automation?

A. Increased quality and production, industrial automation, and process control have widely reduced the need for human sensory and mental requirements. The manufacturing flexibility is increased and the manufacturing process can be easily converted with the same production line.

18. Explain derating factor?

A. It is the factor in which the ratings of the parts of the components are decreased so that it will be safe for to use it in critical applications and also it can be used for extreme environmental conditions.

19. What does PID stands for?

A. Proportional integral derivative

20. What is PID based control system?

A. In closed-loop control system an algorithm is used which is PID, and the PID controllers are used to control the closed-loop control in plants. PID controllers are mostly used for independent loops.

21. Explain smart transmitter?

A. In a smart transmitter it would have a microprocessor in its electronic section and because of this, it can do remote digital communications and also we can set the device from a remote position.

22. Explain the difference between the two wire, three wire and four wire transmitter?

A. The power signal transmission is done in a single cable for a two-wire transmitter. The data signal and power are related to common ground in a three-wire transmitter, while in the case of four-wire transmitter two wires are used for supply power, and for signals, two wires are used.

23. Explain fieldbus?

A. A field bus is a communication protocol and it is digital, in-fact it is a high speed communication protocol. With the help of the field bus higher speed communication is possible and it can communicate with multiple transmitters in the same filed wiring.

24. What are the required features for a good automation tool?

A. It should support multiple frame work

     It should be able to identify the object

     It should be able to test the image and object

     It must need better debugging facility

25. Explain the cold junction compensation?

A. The instrument will not be set to 0 degree Celsius because of the industry standards instead of that it will be set to room temperature. Because of this the EMF must be changed and this is called cold junction compensation.

26. What is a pneumatic system?

A. It is a system that uses air to operate the control valves and actuators

27. What are the factors that must be considered while selecting a sensor?

A. Accuracy

Environmental conditions

We must consider the sensor measurement limit


The sensor should be capable to detect the smallest change

28. What are the types of temperature sensors?

A. Thermocouple, resistance temperature detectors, thermistors,

29. What are the required elements for an automation system?

A. The required elements of automated systems are, they should have the power to accomplish the process and operate the system, in order to direct the process it would need a program of instructions, and actuate the instructions it would need a control system.

30. What are the output devices that is used in industrial automation?

A. The output devices such as actuator, drives, control valves, solenoid valves, coils, indicating lamps, etc can be seen in industrial automation.

31. What is the purpose of sensors and transmitters in automation?

A. The sensors can sense the input parameters and the transmitter is used to transmit the electrical signal or it can transmit the out.

32. What is the importance of PLC in industrial automation?

A. A PLC is a computerized industrial computer that is capable to do discreet or sequential logic in a factory environment. It replaces timers, relays, counters, etc.

33. Explain the positive and negative feedback system?

A. In a negative feedback system the output will be removed from the controller while in a positive feedback system the output will be added to the controller.

34. What are the types of pressure sensors that is used for pressure measurement?

A.  Manometers, DP transmitter, Bellows, bourdon tubes and diaphragm elements.

35. Explain open loop and closed loop control system?

A. The out-put of open-loop control system doesn’t make any effect on the output of the controller and the controller would have high gain in this type of control system. In a closed-loop system, the system output would affect the controller output.

36. Explain the function of smart regulator of the PID controller?

A. Most of the PID’s are loaded with self-tuning parameters and this feature is known as a smart regulator. With the help of the smart regulator, the PID can vary the parameters automatically using intelligent adjustment.

37. Name the types of control valves that is used in industries and their functions?

A. The control valves such as gate, ball, diaphragm, butterfly, and plug valves are used for ON-OFF services. While certain control valves such as the globe and pinch valves are used for throttling services and the check valves are used to do the throttling services.

38. What is active and passive sensor?

A. Active sensors are sensors that needs the power supply, photoconductive cell is an example for this. While the passive sensors doesn’t need a power supply an example for this would be radiometer.

39. What are the types of sensors used for industrial automation?

A.  There are different types of sensors used in industrial automation and these sensors can be calssified according to their properties.

Classification of sensors based on properties

Temperature – RTD, thermistors etc

Pressure – LVDT, Fiber optic etc

Level sensors – Thermal, differential pressure etc

Flow – Differential pressure, positional displacement etc

Proximity & displacement – Ultrasonic, LVDT etc

Certain other sensors are also used for industrial automation like speed sensor, moisture humidity sensor.

40. What is an actuator, and what does it do?

A. Actuator is a major part of the control system, which is capable to change the output of a microprocessor or control system into a control action.

41. Explain pneumatic actuators?

A. The pneumatic actuator will use the air to do certain functions, these actuators use the air to do the control action in a machine.

42. What is hydraulic actuators?

A. This type of actuator uses the fluid power to do the control action in a machine

43. Explain the infinite position valve and finite position valve?

A. The control valves could be either finite position or infinite position valves, the infinite position valve can be set in between the fully opened to the fully closed position. The finite position valve cannot be set like the infinite position valve it could either be completely open or completely closed

44. How to check the zero of a DP level transmitter while it is in line?

A. At, first close the isolation valves then open the vent valve on the LP leg and HP leg drain and then check and adjust zero if needed.

45. Explain the difference between the two wire and three wire RTD system?

A. The two wire RTD’s are used for small distance while the three wire RTD is used for long distance.

46. Is there any limitation for level troll?

A. The major limitation of the level troll is that it can’t be used for lengths that is more than 70 inches.

47. What is the purpose of suppression and elevation?

A. Suppression and elevation is used for level measurement if the transmitter couldn’t be installed to the zero levels of the tank

48. If a displacer has hole in it while in line what could happen?

A. There would be only minimum output

49. If the displacer has fallen down while in line then what could happen?

A.  Then the output will be maximum

50. Explain the interface level and how can we calculate it?

A. If a tank is filled with two liquids that have two different specific gravities and this level measurement is the interface level.

It can be calculated by the formulae DP= H (D-d)

H=height      D= specific gravity of the liquid that is below in the tank

d= is the specific gravity of the liquid with is above the tank or it has less specific gravity when compared to the other liquid in the tank.

51. What is plant automation?

A. in industrial automation systems, the technical process would contain many multiple subprocesses and it can be seen in the entire plant.


post-graduate in Electronics & communication.

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