Interview questions based on temperature measurement?

instrumentation
temperature

#1

What are the instruments used to measure temperature?

Thermometer, Thermocouple, Resistance temperature detector (RTD), Optical pyrometer, Bi-metallic temperature indicator.

Choose an instrument from the following which converts heat energy into electrical energy? say why?

A. RTD
B. Thermocouple
C. Thermister

Answer: B, Thermocouple

RTD and Thermister convert the change in resistance to electrical energy, of course, the change in resistance occurs when these devices are subjected to heat. While thermocouple directly converts heat energy to electrical energy.

What is the name of the cable used to connect a thermocouple to a measuring instrument?

Compensating cable

What is ambient temperature ?

The temperature of the environment where the measuring devices and computers are kept. Ambient temperature is considered while measuring temperature.

What is the main difference between RTD and Thermister ?

RTD have positive temperature coefficient & Thermister have negative temperature coefficient

What is mean by +ve and -ve temperature coefficient ?

  • For + ve temperature coefficient, when the temperature increases the resistance of the element used for sensing increases.

  • For - ve temperature coefficient, when the temperature increases the resistance of the element used for sensing decreases.

What is Pt100?

Platinum 100 which is commonly used in RTDs.
At 0degree celsius temperature platinum gives 100ohm resistance, that’s it got name PT100.

Write the Fahrenheit to Centigrade temperature conversion formula?

Deg C = ( Deg F – 32 ) / 1.8

What are Cold junction and Hot junction in a thermocouple?

Cold junction is the reference junction aways kept at 0degree celsius temperature, to avoid the effect of ambient temperature (room temperature).

Hot junction is exposed to varying heat for which the temperature measurement should take. Where the dissimilar metals are joined.

How to identify an RTD and a thermocouple?

Connect a multimeter in resistance mode to the transmitter. If there is reading in ohms then it is RTD otherwise, it is a thermocouple.

Always thermocouple shows mV reading and RTD gives ohms reading.