Temperature dependent workplaces are the heart of industrial civilization. Powerful and controllable energy source are the most important demand of an industry. Boiler, heat exchangers provide this energy to these industries. The temperature of these sources must be controlled by means of controlling the heater coils or the flame so that it cannot damage complete system by excessive heating or else. Various temperature controlling system are hence employed to achieve this objective.

The basic concept is to sense the current status of the system and to control the source generating the heat. Various extra enhancement are like provision of a set point Valve; display status on screen etc. can be added.

The phenomenon of temperature sensing is not measurable by basic standards method, direct comparison purpose. When a Body gets heated or cooled various primary effects take place and one of these effects can be employed for measuring purpose like,

1. Changing in physical or chemical state

2. Change in dimensions

3. Variation in electrical properties

4. E.M.F. generation

5. Change in intensity of total radiation emitted

The various sensors that can be used are of type

1. Mechanical type

2. Liquid in glass thermometer

3. Liquid filled system

4. Vapor pressure thermometer

5. Resistance type temperature sensor

6. Thermostat

7. Thermocouples