# Instrumentation Interview Questions - Based on Temperature measurement

#1

## 1. What are the main reason for temperature measurement?

The important reasons for temperature measurement are:

• To ensure the safety of personnel and equipment by maintaining temperatures within design limits.
• To ensure accurate process control.
• To ensure the product quality.

## 2. Equation for converts degree Celsius to degree Fahrenheit:

°F = °C x 9/5 + 32

-250 to +850°C

## 4. What is the operating principle of RTD?

RTD is based on the fact that a metal’s electrical resistance varies with temperature changes. If a metal wire is heated, according to the equation, its electrical resistance will increase:

Rt = Ro(1+At+Bt2+……)

Where,
Rt = resistance of the metal at TC
Ro= resistance of the metal at 0C
a, b= Constants

## 7. Which type of RTD is used in PDO for safeguarding the equipment like pump bearing, pump casing and for control applications?

Nickel and Copper RTD’s

## 8. What is the operating principle of a Thermocouple?

Simply, the thermocouple is two metallurgical dissimilar metals joined at one end and connected to a millivolt meter at the other end. These ends are called “hot junction” and “cold junction” (reference junction).

Thermocouple is an electrical type sensor.

## 9. What is Seebeck Effect?

If two metal wires form a closed circuit and the two junctions of the metals are at different temperatures, an electrical current in the circuit is found to flow.

## 10. What is the function of Temperature switch?

A temperature switch is an instrument that automatically senses a change in the temperature measured and when a predetermined temperature is reached, opens or closes an electrical switch element.

## 11. What is the function of Temperature Transmitter?

The function of the temperature transmitter is to sense the transmitter of the process, convert the temperature into mA or mV and transmit it to the secondary instruments in a control room.

## 12. What is a thermopile?

A thermopile is a group of thermocouples connected in series.

## 15. What are thermowells?

Thermowells are built from solid drilled-out bar stock and are designed to protect a sensor from flow, high pressure and harsh environments. A thermowell has the added advantages of allowing the sensing device to be removed or replaced without the process tank or piping being opened.

## 16. What is the purpose of Thermowell?

• To protect the temperature sensor from the process environment.
• Helps for easy installation or replacement of the sensor without shutting down the plant.
• Withstand the static and cyclic forces encountered in the process line.

## 17. What is the use of Decade resistance box?

The 8-decade resistance box is ideal for simulating resistance transducers for workshop and field use.

## 18. What are the different temperature calibration devices?

• Millivolt Calibrator
• Muti-loop Calibrator
• Precision temperature calibrator
• Fluidised calibration bath