There are many kinds of thermistors, generally according to the resistance temperature coefficient can be divided into negative resistance temperature coefficient (hereinafter referred to as negative temperature system thermistor number) and positive resistance temperature coefficient (hereinafter referred to as positive temperature coefficient) thermistors; According to the change of resistance value with temperature, it can be divided into: slow change and mutant type; According to its heating mode can be divided into: direct heat type and side heat type; According to its operating temperature range can be divided into: room temperature, high temperature and ultra-low temperature thermistor; According to its structure classification are: rod, round, square, gasket, ball, wire tube, film and thick film and other thermistors