Thermal Probes in Electric Motors: PTC, NTC, RTD ... What Sets Them Apart? ====================================================================== The measurement of the temperature of the winding using PTC screw in thermal sensor inside an electric motor is one of the main data for its protection. These probes will provide an alarm signal when the T overcomes a certain value. Those of us who are dedicated to the maintenance of electric motors often find different devices to measure the temperature. It is very important to identify them well so that they can be replaced correctly if necessary, for example when rewinding an engine.
Here is a review of the most common: Thermistors or bimetals with PTC screw in thermal sensor: The bimetallic thermostats both in strips and discs, which convert a change of temperature into a mechanical movement, are the best-known bimetallic objects due to their name. They are composed of two layers of metals with different thermal coefficients of expansion, so when changing the temperature tends to flex towards the side of lower coefficient of expansion. This arrangement is used in current circuit breakers, where the current flowing through the same bimetal heats it and opens the circuit, thus limiting the maximum current. Thermocouple:
A thermocouple (also called thermocouple) with PTC screw in thermal sensor is a transducer formed by the union of two different metals that produces a voltage (Seebeck effect), which is a function of the temperature difference between one of the ends called "hot spot" or hot junction or measure and the other called "cold spot" or cold or reference union. It basically consists of a closed circuit PTC screw in thermal sensor formed by two determined threads of different metals joined by their respective ends, in which a small current appears from a potential difference arising from a temperature difference at both ends.
The phenomenon is the result of the transit of electrons between the junctions of the two metals as a result of energy, in this case thermal, applied to one of them. The output signal is very low level, between 0.002 to 80 mV; the way to transmit the signal is by means of compensation cables (wires of the same metals as the thermocouple) or by converting this signal to 4, 20 mA. Source Link - https://goldaircontrol.wordpress.com/2018/04/07/thermal-probes-in-electricmotors-ptc-ntc-rtd-what-sets-them-apart/