Application of radiometric temperature determination methods to semiconductor gas sensors

A radiometric method for the determination of the operating surface temperature of very small objects to within ±5 K has been applied to commercial semiconductor gas sensors operated in a static atmosphere. The method involves the collection of the infrared (IR) emission spectrum of the sensor at regular intervals over the operating heater voltage range, followed by the fitting of ambient-corrected Planck functions to determine the temperature at each voltage. At least one independent calibrating temperature measurement (to eliminate the effects of sensor emissivity and spectrometer response) is obtained using the known melting point of an inorganic salt. The operating voltage–temperature relationships for two popular Figaro tin oxide sensors were found to be pseudo-linear and are reported as T=103 V+214±3 K for the Figaro TGS813 sensor with its base removed, T=101 V+224±5 K for the TGS813 with its base attached, and T=106 V+238±5 K for the Figaro TGS2611 sensor. (The temperature of the sensors does not rise appreciably above ambient when they are operated below 0.5 V.) These results indicate that sensor temperatures are significantly higher than most previously reported estimates, particularly those made using infrared thermometers (IRTs). A heat loss model for the sensors is discussed, and the calibration of the heater resistance–temperature relationship is achieved for the TGS2611.