A primary standard high vacuum calibration station for industrial applications

Abstract

The Metrology Laboratory at Lockheed Martin Missiles & Space in Sunnyvale, CA, has developed a primary standard high vacuum calibration station. Maintaining an in-house capability for calibrating Bayard–Alpert gauge tubes and spinning rotor gauges (SRGs) at the primary level eliminates the need for external sources of calibration. This not only significantly reduces costs but also provides for continuous monitoring of the reference standards used to support research programs and manufacturing processes. A constant volume, pressure drop flowmeter is used to generate known pressures in a vacuum chamber partitioned by an orifice of calculable conductance. Data are presented which show vacuum chamber pressure to be directly proportional to flowmeter pressure drop in the three decades of vacuum spanned by the SRGs (10−3–10−6 Torr). Using a SRG calibrated at the National Institute of Standards and Technology, the proportionality constant is determined and shown to agree well with the constant calculated from system fixed parameters and measured pressure ratios. A new design of flowmeter is discussed. An estimate of when the system will be fully utilized as a primary reference will be made.