Temperature measurement test questions

1. What instrument is used to measure temperature?
● Thermometer,
● Bimetal temperature indicator,
● Thermocouples,
● Resistance temperature detector,
● Optical pyrometer.

2. What is a standard temperature sensor?
1. Thermocouple
2. Thermal resistance

3. Write the conversion formula of temperature from Fahrenheit to Celsius?
Degrees C=(Degrees F – 32)/1.8

4. What is the difference between 'Centrigrade' and 'Celsius'?
It's one thing. Celsius is the technical name. In short, Celsius is a scale in hundreds.

5. What are thermocouples? How does it work?
Two different metals are welded (joined) at one end to form a "hot joint" and the other end to form a "cold joint".
When there is a temperature difference between the "hot" and "cold" junctions, mv proportional to the temperature difference will be generated in the circuit.
The mv generated by the thermocouple depends on the characteristics and types of the thermocouple, such as "j", "k" type, etc.

6. What is the range of different thermocouples?
The following thermocouples can accurately measure the temperature within the specified range:
Copper constantan: 0-300 ℃
Iron constantan: 0-600 ℃
Chromium nickel aluminum nickel thermocouple: 0-1200 ℃
Platinum rhodium alloy: 0-2000 ℃

7. What are the names of common thermocouples?
On the bearing of the pump: iron constantan
Combustion chamber of gas turbine: chrome nickel aluminum

8. What is the name of the cable connecting thermocouple and measuring instrument?
The intermediate cable used to connect the thermocouple from the field to the instrument in the control room is called "compensation cable".

9. What is cold end compensation?
"Cold junction compensation" is used for temperature measurement through thermocouple. This compensation is to correct errors caused by room temperature (ambient).
The mv generated by the thermocouple is proportional to the temperature difference between its "hot" and "cold" junctions. The cold end is the ambient temperature (control room).
If there is no "cold end compensation", the temperature measurement of the hot end will be inaccurate.

10. What is RTD? How does it work?
RDT – Resistance Temperature Detector
RTD is a positive temperature coefficient resistor, whose resistance increases linearly with temperature.

11. What is the common RTD?
Pt 100 platinum resistance 100 ohms

12. What is "pt 100"? What is the resistance (in ohms) of pt100 at 0 ℃?
Pt 100 platinum resistance, providing 100 ohms at 0 ℃.

13. What are the advantages and disadvantages of RTD compared with thermocouple?
RTD is accurate in the lower temperature measurement range, such as - 200 ℃ to+200 ℃.
Compared with thermocouples, RTDs are expensive and have limitations in measuring in a higher temperature range.

14. Why does RTD measurement use 3-wire for field signal connection?

The 3-wire system is used for temperature measurement through RTD to compensate line resistance. The three wire system provides a Wheatstone bridge in the measuring instrument.

15. What is a "bimetal" temperature instrument? How does it work? for instance?
In bimetallic temperature instruments, two metals with different temperature expansion coefficients are connected together.
Due to its expansion characteristics, the response of higher expansion coefficient is greater than that of lower expansion coefficient, and distortion is formed on the element. This principle is used to design a low range thermometer.
Most temperature indicators are bimetallic except for filled in instruments.

16. What is a "filled" temperature instrument? for instance?
The principle that liquid expansion changes with temperature is used to design a "filled" temperature measuring instrument.
For example: glass thermometer, filled capillary thermometer and switch.
The filled temperature measuring instrument is used for temperature measurement in the lower range.

17. What instruments are used to measure temperature?
Precision glass thermometer
The RTD is equipped with a resistance meter in Deg C or Deg F.
Thermocouples and mv meters (expressed in Deg C or Deg F).