Vacuum gauge calibration by a combination of expansion and pumpdown methods

A combined approach to the calibration of vacuum gauges is described. It is based on the principle of expansion and pumpdown methods. Two chambers V1 and V2 are connected by conductance Ck. Gas is first expanded into V1 (expansion method), admitted into V2 via Ck, and then pumped away through an orifice of conductance C2. The pressure P2 in V2 decreases exponentially (pumpdown method). A formula for computing P2 is given. Calibration of a Bayard–Alpert type ionization gauge has been carried out in the range 10−4–5×10−7 Torr (1.3×10−2–6.7×10−5 Pa). Possible experimental errors are discussed. A total uncertainty of about 5.2% has been estimated.