Temperature Sensor

Polymer thermal switches are comprised of a crystalline polymer matrix containing conductive particles. Below a critical temperature, the polymer matrix is dense enough to allow the conducting particles to form a continuous network. Above the critical, or "switching", temperature, the polymer expands and breaks the conductive particle network, opening the circuit. Upon cooling, the polymer contracts and the circuit is restored. Typical applications include over-current protection for sensitive electrical systems.

Bimetallic and polymer thermal switches offer precise switching temperatures and quick response times. They are more desirable than thermocouples, which need a reference temperature, and thermistors, which do not have a large enough increase in resistance. Both bimetallic and polymer thermal switches are small, lightweight, and come in a variety of shapes.

References:
"PolySwitch" from Tyco Electronics
http://www.circuitprotection.com

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