Calibration to High Precision in the Medium Vacuum Range with Stable Environments and Micromanometer

Ultrastable vacuum environments are combined with a micrometer-point contact manometer to obtain a calibration uncertainty of 1.2×10−4 Torr + 6 parts in 105 of the reading for the range 1×10−4 Torr to several Torr. The stable pressures are generated with a dynamic vacuum system and a servo control loop which employs cascaded error signals from a capacitance-diaphragm gauge to obtain pressure stabilities of better than ±1 part in 105 at 1 Torr. Precise evaluation of systems and procedures is given. Operational factors that affect accuracy were studied, for example, sorption in the manometer fluid, pressure distribution in the test chamber, time constants of the micromanometer, and thermal response of the control loop.