Mass spectrometer

Abstract

In a mass spectrometer, a detector generates a current-pulse signal corresponding to an incident ion, with a gain corresponding to a detector voltage which is given by a voltage-generating section. A branching section divides, into branches, a voltage-pulse signal which is based on the current-pulse signal taken from the detector's anode. A pulse-counting section detects the signal one branch by a pulse-count method. An analog detection section detects the signal in another branch by an analogue detection method. A conversion-information storage section holds conversion information showing a relationship between an unsaturated predetermined pulse-count value and the corresponding analog detection value under the detector voltage given to the detector during a measurement. A converted-count-value calculation section calculates a converted count value when the pulse-count value or the analog detection value obtained by a measurement exceeds a predetermined value, using the analog detection value obtained by the measurement and the conversion information.