Temperature switches are generally used in industry for limiting temperature. They monitor the temperature of machinery and equipment and, for example, switch off machinery if it overheats or switch on a fan to cool the equipment.
Bimetals form the basis of the WIKA TFS35 temperature switches. Temperature sensing is carried out by a bimetal disc, which snaps over when the nominal switching temperature (NST) is reached.
On cooling back down to the reset switching temperature (RST), the switch returns to its original state.
The bimetal disc in the model TFS35 bimetal temperature switch carrys no current, and this eliminates the possibility of arcing.
With current-carrying bimetal discs there is also a danger of premature switching as a result of higher self-heating.
The reset switching temperature is typically 15 ... 30 K below the switching temperature.
The model TFS35 bimetal temperature switch can be delivered in two contact designs.
A Normally Closed (NC = closed in the normal state) opens a circuit and shuts down the machinery.
A Normally Open (NO = open in the normal state) closes a circuit on reaching the switching temperature, in order that, for example, a fan or warning lamp can be switched on.
In both cases, on cooling down below the reset switching temperature, the contacts return to their original state, so that the monitored equipment can again work normally.