ISO 20486:2017 pdf download

ISO 20486:2017 pdf download.Non-destructive testing — Leak testing — Calibration of reference leaks for gases
1 Scope
This document specifies the calibration of those leaks that are used for the adjustment of leak detectors for the determination of leakage rate in everyday use. One type of calibration method is a comparison with a reference leak. In this way, the leaks used for routine use become traceable to a primary standard. In other calibration methods, the value of vapour pressure was measured directly or calculated over a known volume. The comparison procedures are preferably applicable to helium leaks, because this test gas can be selectively measured by a mass spectrometer leak detector (MSLD) (the definition of MSLD is given in ISO 20484). Calibration by comparison (see methods A, A s , B and B s below) with known reference leaks is easily possible for leaks with reservoir and leakage rates below 10 −7 Pa·m 3 /s. Figure 1 gives an overview of the different recommended calibration methods.
3.1 unknown leak
leak having a stable and repeatable leakage rate of known order of magnitude that can be determined by calibration
3.2 reference leak
calibrated leak which may be used to calibrate another leak
Note 1 to entry: The uncertainty of the reference leak is lower than the required uncertainty of the leak to be calibrated.
3.3 calibration
set of operations which establish, under specified conditions, the relationship between leakage rate values represented by an unknown leak and the corresponding known values of the leakage rate
Note 1 to entry: In the case of calibration by comparison, the known values of the leakage rate are represented by a reference leak.
Note 2 to entry: Normally, the result of a calibration is given as the leakage rate value for the reference leak with a standard uncertainty.
3.4 nominal leakage rate
leakage rate of a leak calculated for specified reference conditions
Note 1 to entry: In leak detection, leakage rates are commonly given in units of pV-throughput (Pa·m 3 /s, mbar l/s,Std cm 3 /min). These are only a precise measure of gas flow if the temperature is given and kept constant. Flow units such as mass flow (g/y) or molar flow (mol/s) are sometimes used to overcome this problem.
4 Nominal leakage rates
Calibrated leaks are only comparable under the same reference conditions. Nominal leakage rates shall be used for comparison. Recommended reference conditions are:
— Ambient temperature:20 °C
— Atmospheric exhaust pressure: 1 000 mbar
— Vacuum exhaust pressure: < 100 mbar
The reference inlet pressure is given by the leak reservoir pressure or the application requirement