| The thermistor is a temperature
dependant resistor. It comes in all shapes, sizes and colours.
The left hand symbol denotes a positive temperature coefficient thermistor. Its resistance rises as the temperature increases. The other symbol denotes a negative temperature coefficient thermistor. Its resistance falls as the temperature increases. |
| Thermistors are often used
in a Wheatstone bridge circuit as shown above.
If the bridge is balanced at a low temperature then the output from the amplifier is zero. If the ambient temperature rises then since both thermistors change in value by the same amount the bridge will remain balanced. If Th1 is used as a temperature
sensor then any changes in temperature affecting its resistance will unbalance
the bridge and give an output from the amplifier.
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