Measuring and testing – Gas analysis – By vibration
Reexamination Certificate
1998-10-06
2001-07-31
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
By vibration
C073S024060, C073S064460, C073S579000, C073S590000
Reexamination Certificate
active
06266996
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of gas sensors, and more particularly to a method and device for measuring concentration and rate of change of concentration of a gas having ability to act as crystal etchant, such as hydrofluoric acid (HF) or deuterium fluoric acid (DF) gas.
2. Description of the Related Prior Art
Chemical lasers, employable in electronic warfare systems, use hydrofluoric acid (HF) or deuterium fluoric acid (DF) gas. To properly diagnose laser operation and to prevent damage to optical elements, it is desirable to be able to determine the concentration and rate of change of the HF or DF gas at several locations in the laser resonator beam path. Therefore, the device should be small and inexpensive so that multiple units may be placed in the same chamber or laser resonator beam path. Presently, there are no such devices available.
The appropriate measuring device should behave as a dosimeter and be able to measure the presence and rate of change of ground-state HF or DF gas in the laser resonator beam path. The HF or DF sensor should further be able to discriminate against other chemical species present in the same chamber. Moreover, since the laser resonator beam path is a very inaccessible and hostile environment, the device should be sturdy and inexpensive, to justify replacement cost. Further, the device should be applicable to other industries which use HF or DF gas, such as semiconductor and oil-refining industries.
Therefore, there is a need for a simple, inexpensive, easily calibratible, efficient and highly sensitive HF or DF sensor, which can be manufactured at high operating margins, does not require a specialized, complicated fabrication process, and which can be used in different industries for measuring HF or DF concentration and rate of change.
SUMMARY OF THE INVENTION
The present invention consists of a method and a device for measuring concentration and rate of change of concentration of HF or DF gas in a chamber, such as a laser resonant beam path. Since the invention is based on subjecting a crystal to erosion by the measured gas, the device is also applicable to any other gaseous industrial crystal etchant.
One embodiment of the present invention is a method for determining concentration of a crystal etchant gas, such as hydrofluoric acid (HF) or deuterium fluoric acid (DF) gas, by subjecting a crystal to erosion by the gas, determining the crystal resonant frequency, which is changeable during the crystal erosion, and calculating the crystal resonant frequency change to determine the concentration of the gas. The step of obtaining the crystal resonant frequency is preferably performed in a Colpitts oscillator. The step of calculating the gas concentration, proportional to a shift in the crystal resonant frequency, may also encompass calculating a change in the gas concentration, calculating a rate of change in the gas concentration, and averaging the calculated gas concentration.
Another embodiment of the present invention is a device for determining concentration and rate of change of concentration of the gas. The device has a crystal being subjected to erosion by the gas, an element for determining the crystal resonant frequency, preferably an oscillator, and a calculating unit for determining the crystal resonant frequency change. The crystal is preferably an AT-cut quartz crystal. The crystal is inserted in a crystal holder, and mounted on an electronic box with the oscillator. It is partially protected with a cover, and can be easily replaced.
The foregoing and additional features and advantages of the present invention will become further apparent from the following detailed description and accompanying drawing figures that follow. In the figures and written description, numerals indicate the various features of the invention, like numerals referring to like features, throughout for the drawing figures and the written description.
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AARL Handbook for Radio Amateurs, 1998 edition, Published by the American Radio Relay League, pp. 14.26, 15.13.
TRW Inc.
Wiggins David J.
Williams Hezron
Yatsko Michael S.
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