Measuring and testing – Barometer
Statutory Invention Registration
1996-02-29
2001-02-06
Tudor, Harold J. (Department: 3641)
Measuring and testing
Barometer
C073S705000, C250S227270
Statutory Invention Registration
active
H0001937
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a pressure measuring instrument, and more particularly to a pressure measuring instrument which utilizes coherent light from a laser to measure the pressure within an enclosed environment, accomplished by the change of the refractive index of a gas in an environment as a function of applied pressure.
BACKGROUND OF THE INVENTION
Pressure instruments that serve as a background for the invention can be grouped into three categories: general purpose pressure instruments; manometers; and piston gauges. General purpose pressure instruments are devices such as Bourdon tube pressure gauges, capacitance diaphragm gauges and pressure transducers which are used to monitor/measure process parameters or as secondary standards used in the calibration of process equipment. Bourdon tube gauges use an elastic tube which flexes as a function of the applied pressure. Capacitance diaphragm gauges use a moveable membrane which varies the capacitance of the sensing element as a function of the applied pressure. Pressure transducers use a strain gauge which changes value as a function of the applied pressure. These instruments either use elastic elements or moving parts.
Manometers are liquid filled devices which measure pressure as a function of the change in height of the column(s) of the liquid. These devices can use water, alcohol, benzine, mercury or other fluids as the measurement medium. The difference in the column heights is monitored with a scale or ruler calibrated in the pressure units of interest. In the most accurate namometers, lasers have been used to measure the column heights. In this fluid based measurement system, it is necessary to change fluids at specified intervals. Because alcohol, benzine and mercury are all RCRA (Resource Conservation Recovery Act) regulated hazardous materials this procedure produces hazardous wastes.
Piston gauges are pressure measurement systems that measure pressure based on the cross sectional area of a piston and an applied mass. These instruments are typically used as primary pressure standards due to the fact that the measurement is based upon the physical quantities of mass and area. During use, a mass consisting of one or more certified weights is placed upon a weight table which is attached to the piston. The applied pressure is then increased or decreased through the use of valves and volume adjusters in order to place the piston and mass on a float, the term float referring to a point when the piston is free to move and encounters no friction forces from the upper or lower physical restraints used to hold the piston within its cylinder. Piston gauges of this caliber are manufactured to extremely tight tolerances. As with the other gauges, piston gauges contain moving parts.
Thus it is an object of the invention to provide a pressure measuring means free from moving parts or elastic elements.
It is another object of this invention to provide a pressure measuring means that reduces, or ultimately eliminates, the use of hazardous waste materials.
It is yet another object of the invention to provide a pressure measuring means that does not require the use of weights to measure pressure.
These objects may be achieved by providing a pressure monitoring apparatus that utilizes changes in laser light energy as a result of modulations or changes in atmospheric pressure to accurately measure pressure within a system or environment.
SUMMARY OF INVENTION
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, a novel apparatus for measuring pressure within an environment is now presented. The pressure measuring instrument described herein utilizes the change of the refractive index of a gas as a function of pressure and the coherent nature of a laser light to determine the pressure within a closed environment. For example, as the gas pressure in a closed tube varies, the index of refraction of the gas changes. The amount of the change in the index of refraction is a function of the gas pressure. By illuminating the gas with a laser light source, a change in pressure within the closed environment which causes the wavelength of the light to change can be quantified by measuring the shift in fringes (alternating light and dark bands produced when coherent light is mixed) in an interferometer. This technique produces a primary measurement standard because the resulting measurement is based upon the wavelength of the laser light. The invention is useful in laboratories as a primary pressure standard to replace means such as existing mercury manometers to achieve accurate pressure measurements.
Still other objects of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein the preferred embodiment of the invention is described. The invention will be set forth in part in the description that follows and in part will become apparent to those so skilled in the art upon examination of the following description or may be learned by practice of the invention. Accordingly, the drawing and description will be regarded as illustrative in nature and not as restrictive.
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patent: 4659923 (1987-04-01), Hicks
patent: 4688940 (1987-08-01), Sommergren et al.
patent: 4702604 (1987-10-01), Achtermann et al.
patent: 4938062 (1990-07-01), Shimizu et al.
patent: 5101664 (1992-04-01), Hockaday et al.
patent: 5363196 (1994-11-01), Cameron
patent: 5414509 (1995-05-01), Veligdan
Abercrombie Kevin R.
Rash Tim
Shiels David
Gottlieb Paul A.
Lucas John T.
Moser William R.
The United States of America as represented by the United States
Tudor Harold J.
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