Study on calibration technology of port quick leak detector for spacecraft

Abstract

In order to reduce measure standard uncertainty and achieve precise calibration of Port Quick Leak Detector in different temperatures under full range, the special calibration apparatus was designed on basis of theoretical studies. This apparatus consists of pressure standard leak system, calibration system, temperature control system, gas supply and pump system. Pressure standard leak system is made up of a series of standard leaks, it provides standard leak by adjusting the inlet gas and outlet gas pressures of standard leak. Calibration system includes measure instrument, calibration chamber, reference chamber, which used for measure the pressure leakage of leak. Temperature control system consists of constant temperature box, temperature control unit, temperature sensor etc. it can change the environment temperature of calibration system from −50°C to 20°C. Gas supply and pumping system comprised of high pressure gas cylinder, vacuum pump. It provides known pressure gas to pressure standard leak system and calibration system, and pumps all the apparatus. This apparatus is based on direct comparison calibration method of constants volume pressure reduction method, the apparatus and Port Quick Leak Detector are measured under same flow leak, which is provided by pressure standard flow system, and its correction factor in full range is gained by comparing both measure values. This apparatus is used symmetry structure for calibration chamber and reference chamber, and hence which can reduce the influence of calibration environment temperature on calibration results, calibration lower limit is extended to 2×10−6Pa·m3/s. By using cycle water system, the influence of initiative constant temperature and passivity constant temperature techniques on the calibration of detector was studied systematically, and the accurate calibration of Port Quick Leak Detector under different temperature was achieved. The effect of inlet and outlet pressures of leak on leakage was investigated, and a corrected formula about the change of leakage with pressure was derived successfully, and a series of standard leaks were provided and the full range calibration of detector is achieved. The calibration range of the resultant apparatus is 2×10−6∼1×10−3Pam3/s with a combined standard uncertainty about 4.7 %, and its calibration temperature is in the range from −50°C to 20°C.