# Instrumentation Interview Questions - Based on Temperature measurement

**URL:** <https://forumautomation.com/t/instrumentation-interview-questions-based-on-temperature-measurement/6266>\
**Category:** Instrumentation\
**Created:** [April 18, 2019, 3:24pm UTC](https://forumautomation.com/t/instrumentation-interview-questions-based-on-temperature-measurement/6266 "2019-04-18T15:24:01Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![sivaranjith](https://forumautomation.com/letter_avatar_proxy/v4/letter/s/ba9def/32.png) [@sivaranjith](https://forumautomation.com/u/sivaranjith)\
**Post date:** [April 18, 2019, 3:24pm UTC](https://forumautomation.com/t/instrumentation-interview-questions-based-on-temperature-measurement/6266/1 "2019-04-18T15:24:01Z")

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## 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**

## 3. What is the temperature range of Platinum RTD?

Answer:

-250 to +850°C

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

Answer:

[**RTD**](https://forumautomation.com/t/resistance-thermometer-rtd-types-materials-and-characteristics-and-calibration/5099) 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

## 5. Draw [Wheatstone bridge](https://automationforum.co/wheatstone-bridge-strain-gauge-operation-and-characteristics/) circuit for 4 wire RTD connection temperature measurement.

Answer:

 ![wheat%20stone%20RTD](https://cdn.forumautomation.com/original/2X/4/48088e0ddbbe518cabbcdc6b13e397ea1f5940ef.png)

## 6. Draw a bird cage RTD and mention its part:

 ![cage%20rtd](https://cdn.forumautomation.com/original/2X/0/035e28e54e13edd552081d8feb940ac875b0fe8b.png)

## 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**](https://forumautomation.com/t/thermocouple-transducer-how-to-costruct-a-thermocouple-device-at-home/2362) 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**](https://forumautomation.com/t/what-is-temperature-transmitter-advantages-and-disadvantages-of-rtd/694) 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.

## 13. Draw a simple sketch of a thermopile setup:

Answer:

 ![thermophile](https://cdn.forumautomation.com/original/2X/2/22f1358929f885f4b3e68f985785cccd80989f60.png)

## 14. Draw a simple sketch of a parallel thermocouple:

Answer:

 ![thermocoupele%20conn](https://cdn.forumautomation.com/original/2X/0/037baa493fa02036d174d3b01e58736a7de7c553.png)

## 15. What are thermowells?

Answer:

[**Thermowells**](https://automationforum.co/thermowells-types-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**](https://forumautomation.com/t/what-are-pyrometers-types-of-pyrometers-non-contacting-type-temperature-measurement/5299): 0 to 3500 degree C

- Optical pyrometer: 350 to 1200 degree C

- Photo-electric pyrometer: 400 to 2000 degree C

## 20. What is the temperature range of Platinum RTD?

Answer:

-250 to +850°C