Method to test linearity of quadrupole mass spectrometers by use of a flowmeter and a standard leak

A linearity test of the quadrupole mass spectrometer signal can be performed by using the pressure generated by the flow rate of a secondary leak as a fix point and varying the flow rate by a primary gas flowmeter around this value. Applying this method, we have investigated three different quadrupole mass spectrometer in a range of helium partial pressures between 10−9 Pa and 10−4 Pa, corresponding to flow rates of 10−7 Pa L s−1 to 10−2 Pa L s−1 in our system. Our preliminary results indicate significant non-linearities for even modest partial pressure changes.