Primary flow meter for calibrating a sniffer test leak artefact by a pressure rise method

Sniffer tests are used to locate leaks in equipment during operation. The sensitivity of a sniffer leak detector must be calibrated against a known gas flow to atmospheric pressure generated by a sniffer test leak artefact. We have developed a primary flow meter for calibrating gas flows to atmospheric pressure through the leak artefact. The flow meter is based on a pressure rise method and two chambers are used to measure the pressure rise with small uncertainty even at atmospheric pressure. The calibration range of the flow rate is 5 × 10−7 Pa m3 s−1 to 7 × 10−4 Pa m3 s−1 to atmospheric pressure at 23.0 °C with a minimum uncertainty of 1.4% (k = 2), as well as 4 × 10−8 Pa m3 s−1 to 5 × 10−4 Pa m3 s−1 to a vacuum at 23.0 °C. The long term stability of the flow meter was determined as 0.41% by repeated measurements of the conductance of the leak artefact. In case of the flow rate into a vacuum, the flow meter was successfully linked to the international reference value of CCM.P-K12 by a lab-internal comparison.