The most important factors that limit measurement performance of high-accuracy low-pressure transducers are: short-term instabilities in the zero-pressure readings, long-term shifts in the transducer calibration with time and, in the case of heated gages, the effect of thermal transpiration at absolute pressures below 100 Pa. A comprehensive study of capacitance diaphragm gages (CDG's) of the types currently being used by calibration laboratories as transfer standards has been carried out. Several hybrid CDG systems, developed at NIST by using thermoelectric heating/cooling modules to control the CDG's near room temperature, have demonstrated that this approach can improve their measurement performance. Somewhat more limited data on alternative low-pressure transducers based on other technologies (e.g., helical quartz tube, resonant structures, etc.) have been obtained and are presented as well.
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