Combined detector capacitor and vacuum feed through

Details Combined detector capacitor and vacuum feed through Combined detector capacitor and vacuum feed through

2000-11-02

2002-07-23

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S301100, C361S277000, C361S279000, C361S303000

Reexamination Certificate

active

06424515

ABSTRACT:

BRIEF DESCRIPTION OF THE INVENTION
This invention relates to capacitors for detecting voltages applied to components in a vacuum enclosure.
BACKGROUND OF THE INVENTION
Mass spectrometers are instruments for analyzing the chemical composition of matter, usually by using electric or magnetic fields to separate ionized particles by their mass-to-charge ratio. For example, in a quadrupole mass spectrometer, the separation is achieved by driving two pairs of electrodes, one pair driven with a selected radio frequency RF voltage summed with a positive direct current DC voltage, and the other pair driven with the 180° out-of-phase RF signal summed with a negative direct current (DC) voltage.
Accurate measurement of the level of RF voltage driving the electrodes is vital to the success of mass spectrometers, both to provide feedback to the RF circuit to ensure the level of RF is the desired level, and to provide the information to the DC control circuit to ensure that the desired ratio of RF to DC voltage is maintained.
Detector capacitors are used to detect the input RF voltage applied to the pairs of rods and provide an output current which is representative of the input RF voltage. The output current is applied to RF and DC control circuits which control the RF and DC input to the mass spectrometer.
Prior art detector capacitors operate at atmospheric pressure and incorporate features which ensure that the capacitance does not change with temperature changes. One prior art design of a detector capacitor uses low thermal coefficient of expansion metal (e.g. Invar composition 36% Ni balance iron) with insulating parts made of low thermal coefficient of expansion insulator (e.g. Quartz or Alumina). Another prior art design uses materials where the coefficient of expansion are arranged so that changes in dimensions act to cancel any change in capacitance.
SUMMARY OF THE INVENTION
The present invention provides a capacitor which is adapted to be mounted on the wall of a vacuum enclosure, such as the manifold of the mass spectrometer evacuation system, with the capacitor plates inside the enclosure, so that the space between the plates is evacuated by the vacuum system, and a feed-through provides a connection to one of the capacitor plates.


REFERENCES:
patent: 4007406 (1977-02-01), Weisbrod
patent: 4914543 (1990-04-01), Carroll et al.
patent: 4924701 (1990-05-01), Delatorre
patent: 5546058 (1996-08-01), Azuma et al.
patent: 5735884 (1998-04-01), Thompson et al.
patent: 5825608 (1998-10-01), Duva et al.
patent: 6064559 (2000-05-01), Church, Jr.
patent: 6349025 (2002-02-01), Fraley et al.
patent: 6351368 (2002-02-01), Kim

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