A method for controlling mass spectrometers and mass spectrometers

A method for controlling a mass spectrometer, comprising: during a period in which a measurement of the partial pressure of a gas to be measured takes place: - supplying a cathode current to a cathode electrode of an ion source comprising the cathode electrode and an anode electrode, and ionizing molecules of a gas to be measured by light emitted from the cathode electrode, thermal electrons, the cathode current of the cathode electrode is supplied so that the between the cathode electrode and the becomes constant anode electrode flowing current emission of thermal electrons; - selecting generated in the ion source ions according to their mass-to-charge ratio; and - detecting the ion current value of the selected ions as the basis of measuring the partial pressure of the gas to be measured; during a period in which no measurement of the partial pressure of the gas to be measured. takes place: - supplying a constant current having a current value smaller than that of the cathode current to the cathode electrode.