Flowmeter for very low gas flows of inert gases

Gas flow was measured by using constant volume-variable pressure method. The gas flow is measured by pressure rise method using spinning rotor gauge (SRG). The design is relatively simple and has no precisely movable parts compared to the constant pressure-variable volume method. Due to outgassing effect we used a non-evaporable getter pump in order to diminish the influence of hydrogen outgassing on measured gas flow. Lower limit of pressure rise method is 5 × 10−10 mbar l/s and this is extended to 3 × 10−12 mbar l/s by using constant conductance method. With this flow meter we generated a calibration pressure of Argon in our calibration system in the range from 8 × 10−13 mbar up to 2 × 10−7 mbar.