Gain control for a quadrupole mass spectrometer

• US 3,946,229 A
• Filed: 03/29/1974
• Issued: 03/23/1976
• Est. Priority Date: 03/29/1974
• Status: Expired due to Term

• Current Assignee: Litton Systems Incorporated (Northrop Grumman Corporation)
• Original Assignee: The Bendix Corporation (Honeywell International Inc.)
• Inventors: Moseman, Paul W. Jr., Carrico, John P., Passeri, David
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US05/456,325
• Time in Patent Office: 725 Days
• Field of Search: 250/292, 250/281, 250/282, 250/283, 250/299, 250/300
• US Class Current: 250/292
• CPC Class Codes: H01J 49/0009 Calibration of the apparatus
• CPC Class Codes: H01J 49/022 Circuit arrangements, e.g. for generating deviation currents or voltages regulating electric or magnetic variables in general, e.g. current, magnetic field G05F; Components associated with high voltage supply high voltage supply per se H02M
• CPC Class Codes: H01J 49/4215 Quadrupole mass filters H01J49/4225 takes precedence

Abstract

A quadrupole mass spectrometer gain control system for continually analyzing a gas mixture with accuracy. A quadrupole mass filter is located in the system to receive the gas mixture output from an ionization source. The quadrupole mass filter is operated in such a manner as to sequentially select the mass channel, detect mass peak amplitudes, and compensate for mass dependencies of individual channels through which an output signal representative of the percentages of an individual gas in the mixture is transmitted to a display. To compensate for system gain variations occurring in the ionization source, mass filter, ion detector, and detector preamplification function, a system gain control is provided in which the sum of the constituent gas amplitudes is compared with a 100% amplitude reference, and the error signal used to control the system gain.

Claims

1. In a quadrupole mass spectrometer wherein a gaseous mixture is sequentially scanned to obtain a measurement of the relative abundance of each component thereof, control means for automatically compensating for variations in ionization, gas transportation and detection efficiencies of said gaseous mixture to continually obtain an accurate analyzation, said control means comprising:

first amplifier means for generating an ion detection signal representative of each component in said gaseous mixture as established through the scanning of the gaseous mixture;

demultiplex means for converting said ion detection signal for each component into a corresponding output signal in synchronization with the sequential scan of the gaseous mixture;

channel means for communicating said output signal to an indicator means to inform an operator of said relationship of each component in said gaseous mixture;

adjustment means associated with said channel means for modifying the output signal of a known gas sample presented to an ionizer to calibrate said indicator means;

first resistor means connected to said channel means for reducing each of said output signals to produce a proportional output signal corresponding to the concentration of each gas in the gaseous mixture;

junction means connected to said first resistor means for combining said proportional output signal of each of said components to produce a component signal;

second amplifier means connected to said junction means for increasing the amplitude of said component signal;

second resistor means associated with said second amplifier means for controlling the gain of the component signal;

comparator means connected to said second amplifier means for comparing said component signal with a reference signal to establish an error signal; and

integrator means having a ramp amplifier and a capacitor means responsive to said error signal for establishing a gain signal for proportionally modifying each of said ion detection signals from said first amplifier means in a manner such that the component signal is brought into equalization with said reference signal in a series of uniform steps.

2. In the quadrupole mass spectrometer, as recited in claim 1, wherein said control means includes:

mass peak detecting and counting means for periodically monitoring the input gas mixture for changes in constituency to produce an evaluation signal representative thereof.

3. In the quadrupole mass spectrometer, as recited in claim 2, wherein said control means further includes:

means for comparing the evaluation signal with a reference signal to produce an alarm signal and thereby inform an operator of the operational parameter.