Interview Related Questions

I have collected few basic and advanced questions which are and may be asked during interviews in companies.

(Sourced from various websites and journals.)

1. Why is 4-20 mA used as standard for measuring?

Ans: It is more linear for most of the readings as the transducer provides non linear values outside this range of 4-20 mA.

2. Why not 0 mA used?

Ans: Apart from non linearity, the standard 0mA is not used for low range of the instrument. Instead when the reading from the instrument is 0mA it means that the instrument is off or cable in between is not connected, or loss of contact.

3. Various kinds of Programming used in modern day PLC/DCS?

Ans: SFC/CFC, Structured Text, Function Block Diagram, Machine Programming also known as Instruction List and Ladder Logic.

About Ladder Logic, Structured Text


4. Types of Architecture of DCS systems.

Ans: Client/Server Network and Ring structure.

5. What is Redundancy in Control Systems.

Ans: Redundancy is having a secondary unit running parallely with the primary unit. Like a secondary controller having a parallel run with the primary controller which is controlling the plant. In case of Primary unit failure, the secondary unit takes over as primary so that the operation doesnt take a hit.

 6.What is a gateway or Router?

A node that is connected to two or more networks is commonly called as router or Gateway. It generally forwards message from one network to another.

7.  What is DNS?

DNS stands for Domain Name System. It is a Naming System for all the resources over Internet which includes Physical nodes and Applications. DNS is a way to locate to a resource easily over a network and serves to be an essential component necessary for the working of Internet.

 8. What is point-point link?

If the physical links are limited to a pair of nodes it is said to be point-point link.

 9. What is DHCP scope?

A scope is a range, or pool, of IP addresses that can be leased to DHCP clients on a given subnet.

 10. What is IP?

It's a unique 32 bits software address of a node in a network.

 11. What is private IP?

Three ranges of IP addresses have been reserved for private address and they are not valid for use on the Internet. If you want to access internet with these address you must have to use proxy server or NAT server (on normal cases the role of proxy server is played by your ISP.).If you do decide to implement a private IP address range, you can use IP addresses from any of the following classes: 

Class A : 
Class B : 
Class C :

12. What can you tell me about the OSI Reference Model?

The OSI Reference Model provides a framework for discussing network design and operations. It groups communication functions into 7 logical layers, each one building on the next. This question will demonstrate whether candidates have the theoretical knowledge to back up their practical skills.

13. What are the use of cross and standard cables? Where do you find their usages?

A Network cable may be crossover as well as straight. Both of these cables have different wires arrangement in them, which serves to fulfill different purpose.

14. Explain the term BOM?

BOM stands for Bill Of Materials; it is a list of item or parts that makeup a product assembly.  For example, a lawn mower requires a handle assembly, metal deck assembly, a control assembly, motor and blade assembly.

15. Explain what is DCR?

DCR stands for Document Change Request, a change request which addresses about a problem with a document, SOP (standard operating procedure) or specification and propose a change to fix it. Involves monetary billing for change or modifications of the deviation from SOP.

16. what is batch production?

Batch production is a manufacturing technique, where components or goods are produced in groups and not in a continuous stream. This methodology is mainly used when similar items are produced together. Eg Pharma, chemicals like pesticide, petochem industries etc.

17. Which of the following is the dynamic characteristics of an instrument ?

1. Sensitivity
2. Reproducibility
3. Dead zone
4. Fidelity

Ans: Fidelity

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