ISO 3567:2011 pdf free download – Vacuum gauges一Calibration by direct comparison with a reference gauge.
6.6 Reference gauge
The reference gauge shall be either a calibrated gauge (normal case), traceable to a vacuum primary or national standard, or an absolute measuring instrument (rare case), traceable to SI units and to which a measurement uncertainty can be attributed. In the first case, the reference gauge shall have a calibration certificate according
to ISO/IEC 17025:2005, 5.10.
It is recommended that the reference gauge have a lower or equal resolution limit and a lower or equal measurement uncertainty than the UUC, when either would be calibrated at a primary standard.
The reference gauge should be calibrated, in accordance with this International Standard, for the type of gas that will be used for the calibration. If the reading of the reference gauge depends on the gas species, it shall be calibrated for the type of gas that will be used for the calibration.
7 Calibration
7.1 Procedure
7.1.1 When operating the gauges, follow the manufacturer’s instructions closely, unless otherwise specified (for example by the customer). If, in later use, a set routine is followed when taking a pressure reading, repeat this routine for the calibration. Always use the reference gauge according to the manufacturer’s instructions and/or the information given in the calibration certificate.
7.1.2 After complete installation of the UUC and reference gauge(s), and when the whole calibration system has been readied, pump down the calibration chamber. A bake-out could be necessary in order to reach a base pressure consistent with the requirement of 6.3.1.
7.1.3 The gauges should be switched on when the pressure in the calibration chamber has reached the operating conditions of the respective gauge (after bake-out during cool-down phase). Allow the gauges and their operational device to warm up and stabilize. The stabilization time depends on the type of gauges and the uncertainty required.
Certain types of gauges will require degassing at certain pressures, which should be done during this stabilization period.
If there are gauge heads kept under vacuum by an isolation valve, this shall be opened only when the pressure in the calibration chamber has dropped below the expected value of pressure in the gauge head and/or full scale of the gauge.
7.1.4 Complete the pump-down until a base pressure pçj consistent with 6.3.1 has been reached. Before starting the calibration, record the base pressure and all zero readings of the gauges. This record could become obsolete in the case of calibrations made in a decreasing sequence and, because of this, calibration should be performed in a rising pressure sequence. If calibrations in decreasing sequence are also to be performed, note that the base pressure and its uncertainty could play a significant role.
Measure base pressure P0 in the same condition of the vacuum system as during the calibration, e.g. the valves corresponding to the UUC and reference gauge in the open position.
7.1.5 Establish the first calibration pressure either statically or by stationary equilibrium, as follows.
a) Static method
Static means that the valve to the pump system is closed and gas is admitted into the calibration chamber until the required pressure value is reached (for target pressure points, see Annex B).
1) Make another record of the base pressure ,o after closing the valve to the pump system and before gas admission if different from that recorded according to 7.1.4.
2) If the pressure rise due to outgassing and desorption in the calibration chamber exceeds one tenth of the lowest calibration pressure 5 mm after closing the valve, use the stationary equilibrium method instead,
3) The target value of pressure shall be hit within a certain range agreed with the customer, If no range has been specified, the realized pressure value shall be within ± 5 % of the agreed target pressure value.