Thermistor temperature reference included Low temperature coefficient of sensitivity Applications: ear thermometer, gas detectors (with additional infrared bandpass filter) The TPS 535 thermopile sensor in TO 5 type housing employs a chip of 1.2 x 1.2 mm2 absorber size and a 30 kV thermistor as temperature reference. The square window opening is equipped with a 5.5 mm longpass (standard) infrared filter. The sensor shows a flat sensitivity characteristics over the wavelength. The TPS 535 can also be equipped with infrared bandpass filters for NDIR gas detection.