An in-situ type vacuum gauge calibration system which can perform both direct and comparative calibration of vacuum gauges has been developed. The two calibrations are a direct evaluation of vacuum gauge in a constant volume chamber and a calibration of vacuum gauge compared by gas volume expansion method. This system consists of a gas feeding chamber, pumps (rotary, scroll, turbo molecular), and three vacuum chambers (A, B, C) with different volumes connected with each other.
By using volume expansion method, the ratios of chamber volumes are obtained and the comparative calibrations are successfully performed. The initial gas pressure of chamber A is read by DPI-515 (digital pressure indicator), prior to gas expansion to another chamber with a larger volume.
The pressures of chambers B and C are measured by CDG (Capacitance Diaphragm Gauge). The CDG for vacuum measurement is attached in the chamber C. Prior to the calibration the CDG's are calibrated by using ultrasonic interferometer manometer. Three thermometers with sensitivity of 0.01 °C are attached to temperature measurement on the chambers surface. This equipment has a full automatic control of valves and vacuum measurement to improve calibration efficiency and measurement accuracy.
This calibration system enables to do both direct and comparative calibration of vacuum gauge in a vacuum system so that it will be useful in many areas of vacuum industry as well as many institutions for vacuum gauge calibration.
|