Thermistor temperature reference included Applications in pyrometers, and - with additional infrared bandpass filters - in gas detectors The TPS 534 thermopile sensor inTO 5 type housing employs a chip of 1.2 x 1.2 mm2 absorber size and a 30 kV thermistor as temperature reference. The round window opening is equipped with a 5.5 m longpass (standard) infrared filter. The sensor shows a flat sensitivity characteristics over the wavelength. Remark: The TPS 534 can also be equipped with infrared bandpass filters for NDIR gas detection.