Measurement of temperature




1.temperature measurement bench with accessories.


Temperature is degree of hotness and coldness of body. It is also defined as the measure of the kinetic energy of the particles in a system. If two system are same temperature then there is no exchange of any properties between two system. In this time body is in thermal equilibrium and no exchange of energy.

 Zeroth law of thermodynamics is in the basis of temperature measurement. According to this law if two system are in thermal equilibrium with third system separately then the two system also thermal equilibrium with each other.

Temperature scale and fixed point

In order to measure the temperature thermometer is constructed. To calibrate a thermometer is to mark a thermometer so that you can use it to measure temperature accurately. A fixed point is a standard degree of hotness or coldness such as the melting point of ice or boiling point of water. A scale may be created by reference to such point the typical fixed  point of the same substance are listed below:

Boiling point of oxygen 182.97

Boiling point of silver 960.80

Boiling point of gold  1063.00

Most popular unit of temperature are as fallows:

  1. Centigrade
  2. Fahrenheit
  3. Kelvin

The conversion are as fallows:

(0°C × 9/5) + 32 = 32°F

0°C + 273.15 = 273.15K

Types of thermometer

Liquid in glass thermometer

This type of thermometer consists of a capillary tube with a bulbous and the working principle of such thermometer is based on the expansion of liquid associated with an increase in temperature for eg: liquid and gas thermometer


A thermocouple consists of two wire of dissimilar metal joined each end. One junction is placed where temperature is to be measured and other is kept at a constant lower temperature. It measure temperature 200- 300 degree Celsius.

Thermistor thermometer

The thermistor is a thermally sensitive variables resister which is made from semiconducting material positive charge in resistance with temperature is grater than increase in metal which means less sensitive instructions is used. The thermometer is usually restricted to an operating range of 200 °C to 250 °C. the thermistor have may other advantage over other thermometer and widely used in industry. They an be small and conquently  permit point sensing and are widely used in rigid response for temperature change. The disadvantage of thermistor includes non – linear output with temperature.

vapor pressure thermometers

In vapor pressure thermometers a highly volatile liquid is used, but only partially occupies the thermometer volume. The liquid begins to vaporize and fills the rest of the volume with steam. As a result, the pressure rises until an equilibrium between the liquid phase and the gas phase is reached. In simple terms, the rising pressure causes the vaporizing particles to be forced back into the liquid state.This equilibrium between vapor and liquid depends on the temperature (cf. vapor pressure curve). If the temperature rises, more liquid will vaporize and the vapor pressure will rise accordingly . This rising vapor pressure is indicated by a Bourdon tube, as with gas filled thermometers. Conversely, a drop in temperature causes part of the gaseous vapor to condense and the vapor pressure to decrease. The indicated temperature decreases.

Resistance thermometer

Resistance thermometers, also called resistance temperature detectors, are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a ceramic or glass core but other constructions are also used. The RTD wire is a pure material, typically platinum, nickel, or copper.

Bimetal thermometer

It use two strips of different metals to convert temperature into mechanical displacement . bimetal thermometers are in expansion simple and durable. As purely mechanical devices, they display only the current temperature on their dial. They can be accurate to about 1% full span

s.n Time(min) Mercury 0°C thermometer Thermistor thermocouple Platinum pt 100
      0°C kohm 0°C mV  
1 0 20 21 11.1 17 0.83  
2 2 29 30 5.9 29 0.9  
3 4 41 41 5.1 40 1.5  
4 6 53 53 3.3 51 1.6  
5 8 70 64 2.5 62 2.1  
6 10 75 73 1.8 73 2.3  
7 12 84 82 1.4 83 3.0  
8 14 92 90 1.2 91 3.1  
9 16 96 94 1 94 3.4  


Hence, the boiling point of water is found to be 96°C in mercury thermometer 94°C in thermocouple and 94.1°C in thermistor thermometer.


Therefore, the most accurate thermometer used here is found to be of mercury thermometer.

Leave a Reply

Your email address will not be published. Required fields are marked *