Top 50 Instrumentation Interview Questions
Instrumentation Interview Questions and Answers
Instrumentation Interview Questions and Answers
There are different questions that you can be asked in an interview for the post of instrument technician, instrumentation engineer, or instrument supervisor.
Most interview questions are related to the industry you are going to apply to, and they prefer a skilled person and have a good knowledge of instruments used in that specific industry.
Here I will try to write the question with answers that are mostly asked for instrumentation professionals.
Q. No. 1:
What is instrumentation?
Ans :
Instrumentation is a branch of science which deals with the measurement and control of process variables in a process.
Q. No. 2
What is the process?
Ans :
The process is defined as the adoption of series of steps or methods to acquire a predefined result.
Q. No. 3
What is a process variable?
Ans :
It is a variable in the process that we are attempting to maintain, measure or control in a process.
Q. No. 4
What are basic process variables?
Ans :
Following are the process variable
Flow
Pressure
Temperature
Level
quality
Q. No. 5
What is flow?
Ans :
A material passing through a specific point at a specific time is called the flow of that material.
Q. No. 6
What are the primary elements used for flow measurement?
Ans :
Orifice plate
Venturi tube
Pitot tube.
Annubars.
Flow Nozzle.
Weir & Flumes
Q. No. 7
What is the unit of flow?
Ans :
Unit of flow is :
kg/ min
tonn/hr
liter/ min
etc
Q. No. 8
What is a controller?
Ans :
The controller is used to control a process variable.
It is used to maintain a process variable to a required value (setpoint).
It is an instrument or device which receives a process variable value measured in the process by a transmitter or sensor, compares this process variable with a set point, and then outputs a control signal to the final control equipment to achieve the desired value of the process variable.
Q. No. 9
What is FCE (Final Control Equipment)?
Ans :
Final Control Equipment is a device that has a direct effect on the process variable, it may be a motor, a valve or a heater, etc.
Q. No. 10
What are the different types of control systems used in Industries?
Ans :
PID Controller based control system
PLC-based control system
DCS based Control system
PC Based automation system
Q. No. 11
What types of sensors are used for measuring different parameters in instrumentation?
Ans :
Temperature sensors
RTD, Thermocouple, Thermister
Pressure Sensor
Borden Tube, Bellows, Strain gauge
Flow sensor
Pitot tube, orifice plate, venturi tube
Level switches and transmitter Conductivity meter
Density meter
Ph meter.
Q. No. 12
What is meant by set point?
Ans :
A specific point or value where we want to maintain the process variable in a process.
Q. No. 13
Which is your favorite instrument?
Ans :
Tell the instrument you have better knowledge because you will be asked more details about that specific instrument.
Q. No. 14
What is manipulated variable?
Ans :
Q. No. 15
What is meant by feedback?
Ans :
Feedback means using output as input back into the control system as a part of chain or cause, and to check the effect.
Q. No. 16
What is accuracy?
Ans :
Accuracy means how close the result of measurement is to show the correct known value, its means how close is an instrument reading to a standard measurement.
If we have a 1 kg weight and one instrument measures it 9.999 kg while another instrument measure it as 9.998 then the first instrument is more accurate than the second instrument.
Q. No. 17
What is precision?
Ans :
Precision means how close is each result of an instrument.
Suppose we measure a weight of 1 kg with an instrument and every time it shows 9.99, that's means this instrument is precise. But if it shows 1 kg in the first reading, in the second 9.99 third 1.1kg, its mean instrument is less precise.
Q. No. 18
What is the resolution of a sensor?
Ans :
Resolution is the smallest quantity change at input a sensor can measure or detect.
Suppose a temperature sensor can measure the temperature change of 1 C° then its resolution is 1 C°, it will not detect a change of 0.9 C° or below this value.
Q. No. 19
What is the dead band?
Ans :
The dead band or dead zone is the band where input change does not affect the output in a control system.
Informally we can say that its difference between the setpoint and process value is acceptable.
Suppose setpoint is 99 and PV is 98.5 then 0.5 is a deadband. A difference of 0.5 between setpoint and PV is acceptable for the controller, we can change the dead band as per our requirements.
Q. No. 20
What is Control Valve?
Ans :
The control valve is referred to as the final control component, it is made up of an actuator, pneumatic device motorize, or hydraulic device which transforms the control signal from the controller into action and regulates the flow in the valve body.
Q. No. 21
What are the types of valves?
Ans :
Following are types of control valve
Gate valve
Globe valve
Check valve
Plug valve
Ball valve
Butterfly valve
Needle valve
Pinch valve
Q. No. 22
What are the parts of the control valve?
Ans :
There are three main parts of a control valve.
1. Actuator
2. Stem
3. Body
Q. No. 23
What are the types of actuators?
Ans :
Three main types of actuator
1. Motorized actuator
2. Pneumatic actuator
3. Hydraulics actuator
Q. No. 24
What is an I/P converter?
Ans :
It is a device that converts a current signal to a standard pneumatic signal. It is a device that has a current input of 4 to 20 mm, and at output standard, pneumatic signal changes from 3 to 15 psi.
Q. No. 25
What is a control valve?
Ans :
A control valve is an instrument that regulates the flow of fluids or gases as the valve position is changed by moving the stem with help of an actuator.
Q. No. 26
What is Cavitation in the control valve?
Ans :
Vapor bubble formations happen when internal pressure falls below the vapor pressure, in liquid flow. Then again pressure rises above the vapor pressure, during the recovery of this pressure bubbles collapse, this time cavitation takes place.
Q. No. 27
what is Flushing in the control valve?
Ans :
Flashing is just the first stage of cavitation, this happens with the liquid flow where the pressure falls below the vapor pressure (same as cavitation) and remains below it. There are two phases, vapor, and liquids, flowing downstream and no collapsing of bubbles.
Q. No. 28
How to perform control valve calibration?
Ans :
For calibration of control valve at the site,
First of all, check that it's mechanically free and no obstruction in the movement of the valve.
Apply a zero set point and check that valve is fully close, if not close the valve and adjust zero.
Then apply a 100 percent setpoint and check that valve is fully open, if not open it full and adjust the span to 20 mA.
Q. No. 29
What is control valve sizing?
Ans :
Control valve sizing is a procedure in which the dynamics of the system are matched to the performance characteristics of the valve. So we ensure that a valve meets all the requirements in the process where we want to use it.
Q. No. 30
What is Pressure definition?
Ans :
Force per unit area is called pressure.
P= F/ A
Q. No. 31
What is the unit of pressure?
Ans :
SI unit of pressure is Pascal.
other common units are
kg/cm2
bar
psi
mmWs
mmHg
etc
Q. No. 32
What are the primary sensing elements for pressure measurement?
Ans :
Following are the primary sensing elements for pressure measurement:
Bourdon tube
diaphragm
bellows
capsule
Q. No. 33
What are the parts of a pressure gauge?
Ans :
Following are the main parts of a pressure gauge:
1. intake point or socket
2. bourdon tube
3. gear
4. pinion
5. hairspring
6. pivot
7. pointer
8. pointer stopper
9. dial
Q. No. 34
What are common problems in the pressure transmitter?
Ans :
Following are common problems in pressure transmitters.
1. Impulse line leak
2. Impulse line blocked
3. Leakage or blockage in equalizing valve.
4. Power loss or voltage drop due to cable etc.
Q. No. 35
How to calibrate a pressure transmitter?
Ans :
Vent both ports of pressure transmitter.
Apply zero range pressure and check zero calibration is ok, 4 mA at the output.
Apply span range pressure and check span calibration is ok if not adjust span at output 20 mA.
Also check the 25%,50%,75%,100% rising and falling calibration is ok.
Make a pre-calibration and after calibration chart for the record.
Q. No. 36
What will you do if the pressure transmitter is showing zero pressure?
Ans :
Check that any blockage or leakage in the take-up point, impulse line, or pressure transmitter input point.
Check whether power 24 volts are OK
Check range and calibration of pressure transmitter.
Q. No. 37
What are the types of manometers?
Ans: Following are the types of manometer;
1. U tube manometer
2. Well type manometer
3. Inclined type manometer
4. Ring balance manometer
5. Micro manometer.
Q. No. 38
How many types of diaphragm do you know?
Ans :
There are two main types of the diaphragm;
1. Flat type
2. Corrugated type
Q. No. 39
How capacitive pressure transducer work?
Ans :
It is made up of two parallel plates like a capacitor, The output of a parallel plate capacitor depends on the gap between its movable and fixed plates. Due to pressure, the gap between the plates is changed so capacitance also changes. This change in capacitance is directly proportional to pressure.
Q. No. 40
What is temperature?
Ans :
The degree of hotness or coldness is called temperature.
Q. No. 41
What is the unit of temperature?
Ans :
1. Centigrade
2. Fornhite
3. Kelvin
4. Rankin
Q. No. 42
What are the primary sensing elements for a temperature measurement?
Ans :
Following are temperature measurement primary sensors.
1. Thermometer
2. Thermostat
3. RTD
4. Thermocouple
Q. No. 43
What are common problems in temperature transmitters?
Ans :
1. Power loss or voltage drop.
2. Sensor open or short
3. Cable open or grounded
4. Transmitter faulty
Q. No. 44
How to calibrate a temperature transmitter?
Ans :
Apply zero range input temperature to a transmitter and check output current 4 mA.
Apply span value temperature at the input and check output current is 20 mA.
Q. No. 45
What is RTD?
Ans :
It is an abbabbreviation of Resistance Temperature Detector. It is used to measure temperature, with an increase in temperature its resistance increases gradually. This resistance change is directly proportional to temperature.
Q. No. 46
What is the output of RTD?
Ans :
The output of an RTD is resistance in ohms.
Q. No. 47
What are types of RTD?
Ans :
There are two main types;
1. Wire-wound RTD
2. Thin-film RTD
Q. No. 48
What are the types of thermocouples?
Ans :
There are many types of thermocouples, these types are based on the construction material of thermocouples, each type has a different range of temperature. Following are the main types of thermocouple :
B type thermocouple
E type thermocouple
J type thermocouple
K type thermocouple
N-type thermocouple
R type thermocouple
S type thermocouple
T type thermocouple
Q. No. 49
How to check a thermocouple?
Ans :
We can check a thermocouple with a multimeter, a good working thermocouple has resistance up to 1 or 2ohmsm. Body toelementt resistance should be megaohm.
For further checking heat up the thermocouple and check the outputmillivoltt.
Q. No. 50
What is the working principle of a thermocouple?
Ans :
A thermocouple works on the basic principle of see back effect. When two dissimilar metals are joint at one end ( hot junction) while another end is openly called ( cold junction). When the hot junction is heated then the voltage is produced at the cold junction, these volts are proportional to temperature.
Top 50 instrumentation interview questions
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