Thermally Coupled Thick-Film Thermistors: Main Properties and Applications

A pair of thick-film segmented thermistors with negative temperature coefficient (NTC) were joined together (back-to-back) to form thermally coupled device. The alumina substrate enables very high galvanic insulation of thermistors and thermal coupling at the same time. The input thermistor
${R}_{{1}}$
in the coupled pair was self-heated at constant voltages and the output thermistor
${R}_{{2}}$
was a heat receiver through the alumina substrate. Custom-designed NTC thick-film thermistor pastes were made out of nickel manganese and modified nickel manganese. Thermistor electrical resistances were measured in a climatic test chamber and the thermistor exponential temperature factor
${B}$
was determined for both pastes. The TCT device was electrically characterized at different ambient temperatures. The input power, heat transfer, resistance, and temperature of both thermistors were measured as a function of input voltage and time. The input and output thermistor temperatures
${T}_{{1}}$
and
${T}_{{2}}$
were obtained using the thermistor resistance and the Steinhart–Hart equation. The device sensitivity and measuring inaccuracy were analyzed. The main advantage of TCT is thermal coupling/electrical decoupling. The applications of TCT device are seen in automotive electronics, home appliances, and power converters to measure output temperature versus input power.