Abstract
This article elucidates the calibration of newly procured spinning rotor gauge (SRG 3) from MKS Instruments, USA using primary vacuum standards: Orifice flow system (OFS) and Static expansion system (SES) established at National Physical Laboratory, India (NPLI) in the range of 10<sup>-4</sup> Pa to 1 Pa and further compared with manufacturer reported value which was calibrated by transfer standard of National Institute of Standards &amp; Technology (NIST). The key parameters to calculate the pressure measured by SRG is the accommodation coefficients. The accommodation coefficients for N<sub>2</sub> gas obtained using OFS, SES, and calibration report form NIST USA (SRG2) are 0.957, 0.961, and 0.954 respectively.
Highlights
As a national metrology institute, NPLI has the responsibility of maintaining the various primary vacuum standards and disseminate the traceability down to secondary and reference standards
This section has two primary vacuum standards Orifice flow system (OFS) and Static expansion system (SES) which measure the pressure in the range of 0.1 Pa to 1 μPa and 0.05 Pa to 10 Pa, respectively with associate uncertainty 2% and 0.4% of the pressure reading at k=2
The ball/tube assembly was fitted with a mini ultra-high vacuum (UHV) right angle valve so that the rotors could be isolated from exposure to air during venting of the chamber for shifting the ball/tube assemblies from one calibration system to the other and back
Summary
As a national metrology institute, NPLI has the responsibility of maintaining the various primary vacuum standards and disseminate the traceability down to secondary and reference standards. There are some defense laboratories, research institutions and accredited laboratories which possess CDGs and SRGs as transfer or secondary standards which need to be calibrated time to time using NPLI primary vacuum standards. The low precision ionization gauges were used as transfer standard for inter-comparisons before high precision SRGs and CDGs came into the existence. This section bought SRG 3 which has pressure measuring range of 1 Pa to 10-4 Pa. Comsa et al first invented the spinning rotor gauge in vacuum and high vacuum range with unmatched accuracy among the existing transfer standards, almost similar to the uncertainty of OFS [5]. NPLI has calibrated the SRG3 using both the primary standards (OFS and SES) and further compared with the value given by SRG2 (transfer standard of NIST)
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