Paper VT-MoM4
New PTB Standard to Provide Traceability for Partial Pressure Measurement

Monday, November 10, 2014, 9:20 am, Room 303

Partial pressure measurement in vacuum by quadrupole mass spectrometer (QMS) is an important tool to control and monitor processes in industry and to measure outgassing rates. It is, however, difficult to obtain reliable results with quadrupole mass spectrometers, since its calibration is ill-defined and at present there is no traceability to any national primary standard.

PTB has recently established a new calibration system to calibrate QMS. It is based on the continuous expansion method and allows generating three partial pressures at the same time in the calibration chamber with pressure ratios between them of a factor of up to 10⁸ with the uncertainty of each partial pressure depending on the value and the gas species. In the minimum the uncertainty of partial pressure is close to 1%. With less accuracy more gas species than three can be mixed.

The flow of desired gas into the calibration chamber is generated by nano-holes, glass capillaries or sintered elements characterized in terms of conductances for some gas species. Since the flow through these conductance elements is of molecular type up to about 10 kPa, the flow can be predicted for any gas species.

Four QMS were characterized with the new system and some results will be given. The first goal with this standard is to test and establish calibration procedures for written standards for several parameters of QMS like sensitivity, minimum partial pressure and minimum concentration.

Support through the EMRP IND12 project is gratefully acknowledged. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.