# Interview questions based Process Control Engineering

#1

## 1. Define process

Any system comprised of a dynamic variable usually involved in manufacturing and production operations. It is defined as a series of operations during which some materials are placed in more useful state.

## 2. What is mathematical modelling? Why do we need mathematical modelling of a process?

Set of equations that characterize the process is termed as Mathematical Modelling.

If the process equipment needs to be available for experimentation the procedure is costly. Therefore we need a simple description of how the process reacts to various inputs, and this is what the mathematical models can provide to the control designer.

##3. Distinguish between continuous process and batch process

A process in which the materials or work flows more or less continuously through a plant apparatus while being treated is termed as a continuous process. The problem of the continuous process is due to load changes.

A process in which the materials or work are stationary at one physical location while being treated is termed as the batch process.

##4. Explain the function of a controller?

A controller receives the process errors from the controlled process, according to the process error the controller initiates corrective action by a signal to the controlling variable.

## 5. Define controller turning

Deciding what values to be used for the adjusted parameters of the controller is called controller turning.

## 6. What is ITAE and when to go for it?

ITAE means Integral Time Absolute Error. To suppress the errors that persist for a long time, the ITAE criterion will tune the controllers better because the presence of large t amplifies the effect of even small errors in the value if integral.

## 7. What are the parameters required to design the best controller?

Process Parameters (K,I), Controller parameters (Kp,Ti, Td),performance creation (ISE, IAE, IATE).

##8. Define ratio control

Ratio control is a special type of feed forward control where two disturbances are measured and held in a ratio to each other.

Cascade control is defined as a control system composed of two loops where the set point of one loop (the inner loop) is the output of the controller of the other loop (the outer loop).

## 10. What is meant by auctioneering control?

Such control configurations select among several measurements the one with the highest value and feed it to the controller. Thus it is a selective controller which possesses several measured outputs and only one manipulated input.

## 11. What are decouplers?

The special element introduced in a system with two strongly interacting loops to cancel the interaction effect between the two loops and thus render two non-interacting control loops is called decoupler.

## 12. When do you use a valve positioner?

If the diaphragm actuator does not supply sufficient force to position the valve accurately and overcome any opposition that flowing conditions create a positioner may be required.

## 13. Differentiate split-range control and selective control

Split-range control system involves one measurement and more than one manipulated variables but selective control system involves one manipulated variables and several controlled outputs.

## 14. What is the need of I/P converter in a control system?

In some process loop the controller is electronic and the final control element is electronic one. To interconnect these two we need a device that should linearly converts electric current in to gas pressure (4-20mA-3 - 15 psi). such device is called I/P converter.

## 15. Differentiate inherent characteristics and installed characteristics of control valve.

Inherent characteristics is which the valve exhibits in the laboratory condition where the pressure drop is held constant. Installed or resultant characteristics is the relationship between flow and stroke when the valve is subjected to pressure conditions of the process