Thermal relays

Thermal switches are used for monitoring / controlling temperature without being connected to an electricity supply. Not only are they small and powerful up to 16 A, but they are also suitable for various range of uses and areas of application. Special models are also available on request for specific applications.

By using a normally closed relay, the circuit is broken upon reaching a defined temperature threshold or temperature that is too low within a predefined temperature range.

By using a normally open relay, the circuit is connected upon reaching a defined temperature threshold or temperature that is too low within a predefined temperature range.

Thermal switch changeovers are used to switch the circuits upon reaching a temperature that is too high or too low within a predefined temperature range. This type of thermal switch can typically be found as a form of ventilation control in fan ovens.

By using a thermal switch latcher, the circuit is broken upon reaching a defined temperature threshold or a temperature that is too low within a predefined temperature range. Thermal switch latchers prevent automatic resetting using a high-value resistance in parallel to the contact system. The circuit is closed only after disconnecting the voltage and a short cooling-off phase.

Thermal switch limiters are used to open the circuit upon reaching a defined temperature threshold or temperature that is too low within a predetermined temperature range. They are not subject to automatic resetting because they are ready to be used again only following a manual resetting.

Thermal two-pole switch limiter type C2B is an innovative 2-point temperature controller switch with a long service life. It opens and closes its two bimetal-based contact systems synchronously as the temperature rises at the preset setpoint. After the thermal switch has cooled down, its contact systems can be manually reset to the original state. This thermal switch can be used perfectly for any application that requires a two-pole switch-off, making the variety of its applications nearly unlimited.

Thermal sensors are crucial for the functionality and the service life of the appliances and systems in which they have been installed.

EAW Relaistechnik offers the installation of NTC, PTC, KTY, PT100, PT500 and PT1000 temperature sensors in the ½-inch housing corresponding to the thermal switches range. This solution allows the easy replacement of traditional bimetal thermostats with temperature sensors using NTC or PTC elements.

PTC thermal sensors are made of materials that conduct electricity better at low temperatures than at high temperatures. Their electrical resistance increases as the temperature rises, which give them a positive temperature coefficient.

PT thermal sensors (platinum resistors) are predominantly used for taking temperature measurements with maximum accuracy, as their resistance has a virtually linear correlation with a rise in temperature. PT sensors are protected from both chemical and mechanical influences on account of their platinum coating, subsequent embedding and, in some cases, even their adaptation to specific applications.

NTC sensors are made from materials that conduct electricity better at high temperatures than at low temperatures. Their electrical resistance decreases as the temperature rises, which give them a negative temperature coefficient.

KTY thermal sensors are rather limited in their accuracy because of their non-linear temperature resistant behavior, thus they must be calibrated with additional electronics for sufficient accuracy. As a result of this, the temperature range for KTY sensors is really quite modest. In contrast, the temperature coefficient of KTY sensors is around twice as high in comparison to PT100 as the effective signal is less vulnerable to disturbances from the environment. The greatest disadvantage of KTY sensors is their sensitivity to electrostatic discharges as the sensors can be slightly damaged by external voltage pulses.