Power supply for multipolar mass filter
First Claim
1. A multipolar mass filter (1) through which charged particles of a selected mass-to-charge ratio may be transmitted in response to the application to its electrodes of an alternating potential of selected amplitude and frequency, said filter comprising resonant circuit means (8) connected to the electrodes (2-5) of said filter, controllable radio-frequency oscillator means (7) for generating said alternating potential at a frequency determined by said resonant circuit means (8) and at an amplitude determined by an amplitude control signal, said mass filter being characterized by means (26-33, 18, 19) for adjusting the amplitude of said alternating potential in response to changes in the actual frequency of oscillation of said oscillator means (7) in order to maintain the transmission through said filter of charged particles of said selected mass-to-charge ratio.
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Accused Products
Abstract
A quadrupole mass filter (1) includes a controllable RF oscillator (7) which follows any drift in the resonant frequency of a resonant circuit means (8), this circuit means (8) amplifying an alternating RF potential from the oscillator (7) and supplying it to the filter electrodes (2, 3, 4, 5). To ensure that the charge to mass ratio of the particles transmitted by the filter remains constant, a signal for controlling the amplitude of the oscillator (7) is corrected in response to any resonant frequency shift. This signal is also fed to DC supply means (12, 13, 15), to ensure that the amplitude of the DC potential applied to the electrodes (2, 3, 4, 5) remains in the correct ratio to the RF potential amplitude so that the filter resolution remains constant.
37 Citations
20 Claims
- 1. A multipolar mass filter (1) through which charged particles of a selected mass-to-charge ratio may be transmitted in response to the application to its electrodes of an alternating potential of selected amplitude and frequency, said filter comprising resonant circuit means (8) connected to the electrodes (2-5) of said filter, controllable radio-frequency oscillator means (7) for generating said alternating potential at a frequency determined by said resonant circuit means (8) and at an amplitude determined by an amplitude control signal, said mass filter being characterized by means (26-33, 18, 19) for adjusting the amplitude of said alternating potential in response to changes in the actual frequency of oscillation of said oscillator means (7) in order to maintain the transmission through said filter of charged particles of said selected mass-to-charge ratio.
- 14. A method of operating a multipolar mass filter (1) through which charged particles of a selected mass-to-charge ratio may be transmitted and to which is applied through resonant circuit means (8) an alternating potential whose frequency is determined by said resonant circuit means and whose amplitude is determined by an amplitude control signal, said method being characterized by adjusting the amplitude of said alternating potential in response to changes in the actual frequency of said alternating potential to maintain the transmission through said mass filter of said charged particles of selected mass-to-charge ratio.
Specification