Thermistors (also known as “PTC- Positive Temperature Coefficient”) are made from a semiconductor material wafer in a ceramic capped. The semiconductor its electrical resistance rises abruptly from a certain temperature called “cut”. Depending on the composition of the thermistor semiconductor material used will have a temperature defined cut. They can be simple or linked as triplet to monitor each of the phases in a three phase machine.
With no moving parts are very reliable and can make an unlimited number of operations.