1.4. A system leakage test shall be performed. The probe shall be disconnected from the exhaust system and the end plugged. The analyser pump shall be switched on. After an initial stabilisation period all flow meters should read zero. If not, the sampling lines shall be checked and the fault corrected. The maximum allowable leakage rate on the vacuum side shall be 0.5% of the in-use flow rate for the portion of the system being checked. The analyser flows and bypass flows may be used to estimate the in-use flow rates.
Another method is the introduction of a concentration step change at the beginning of the sampling line by switching from zero to span gas.
If after an adequate period of time the reading shows a lower concentration compared to the introduced concentration, this points to calibration or leakage problems.