# Instrumentation Interview Questions - Based on Temperature measurement

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

Answer:

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:

Answer:

°F = °C x 9/5 + 32

Answer:

-250 to +850°C

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

Answer:

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

Answer:

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

Answer:

Nickel and Copper RTD’s

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

Answer:

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?

Answer:

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?

Answer:

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?

Answer:

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?

Answer:

A thermopile is a group of thermocouples connected in series.

Answer:

Answer:

## 15. What are thermowells?

Answer:

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?

Answer:

• 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?

Answer:

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

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

Answer:

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

## 19. Write the temperature range of Pyrometers

Answer:

• Radiation pyrometer: 0 to 3500 degree C

• Optical pyrometer: 350 to 1200 degree C

• Photo-electric pyrometer: 400 to 2000 degree C

Answer:

-250 to +850°C