PTC thermistors

PTC thermistors (Positive Temperature Coefficient) are electrical sensors inserted into the winding. Their internal resistance increases as the temperature rises. In addition to the motor protection switch (overcurrent), PTC is an additional thermal protection (overtemperature) and is therefore highly recommended. Elevated temperatures damage the motor and cause it to fail prematurely.
PTC relays must be approved for use in biogas plants in hazardous areas. However, the PTC sensor itself does not require this approval. The PTC is only partially relevant for an Ex assessment: This is because the agitator in the Optimix should only be operated completely immersed in the substrate - using the immersion probe would be one option for this. There is no risk of explosion if the substrate overheats. At most, the substrate will start to boil in the area of the Optimix housing.