It is a resistor whose resistance changes with change in temperature. As we already know that resistance is dependent on temperature. This is the only principle in the working of a thermistor. The change in resistance depends on the type of material used. Their cost is very less are very efficient. We can find them in many areas. But do not work well in extremely hot and cold weather.
Thermistor Symbol
The symbol of thermistor is
When two two or more metallic oxide semiconductors are mixed together a slurry is formed. This mixture will form slurry. We prepare it on a wire. We keep it in a sintering furnace to cool down. This cause the slurry to shrink. As we keep it on wire it also forms an electrical connection. We now apply a coat of glass on it. The coat of glass prevents it from water. It will increases its stability.
Working of Thermistor
We use ohmmeter to measure value of resistance. The thermistor has resistance depending on the temperature. We see from figure that change in temperature will bring corresponding change in resistance. The resistance is measured through ohmmeter. The temperature and resistance characteristics is below which shows how the change in resistance with temperature is dependent on the type of material it is made of.
There are two types of thermistors
Negative temperature coefficient:
In negative temperature coefficient type of thermistor the resistance will decrease when temperature increases and vice versa. The NTC are mainly in use. The temperature and resistance relationship is given as
RT =R0
Where:
- RT is the resistance at temperature T (K)
- R0 is the resistance at temperature T0 (K)
- T0 is the reference temperature (normally 25 degree Centigrade)
Positive temperature coefficient:
In positive temperature coefficient type of thermistor the resistance will increases with increase in temperature and vice versa.
Application
We can find them in many fields. For measurement of temperature. Some of its applications are digital thermometer. In microwaves thermistor is used. We also find them in rechargeable batteries and wheat stone bridge.
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