Development of a high precision quadrupole mass filter using the zero-method control circuit

A high precision quadrupole mass filter has been developed using the zero-method control circuit. With this method, peak values of a control voltage are compared with a high-precision reference voltage and detected by a diode and signal-producing resistance connected in series. The dc component of the signal is selectively amplified and fed back to a module in the amplifying system of the rf voltage so as to minimize the voltage in excess of the reference voltage. An instrument has been constructed and the doublet of 4He+–D2+ has been successfully separated.