Measuring and testing – Gas analysis – Gas of combustion
Reexamination Certificate
1998-11-16
2001-08-28
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Gas of combustion
C073S863810, C073S001060, C422S003000, C204S401000
Reexamination Certificate
active
06279377
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to comparison of concentration of a gas with a threshold, and more particularly to monitoring of oxygen concentration and annunciating results of such monitoring for plural thresholds and values, using only a single calibration concentration.
BACKGROUND ART
Hazards of excessive or inadequate concentration of specific gases exist in many forms. For example, low oxygen levels may lead to asphyxiation. On the other hand, excessive oxygen levels may create a combustion hazard. However, various industrial processes require large amounts of liquid or gaseous nitrogen and oxygen. Thus, in the home health care environment, it is desirable to monitor the output of an oxygen concentrator to determine whether the output oxygen level remains above (or falls below) a predetermined minimum desired limit. In other industrial and commercial applications, it is desirable to maintain oxygen concentration between preset lower and upper limits.
Accordingly, the presence or absence of oxygen or other gaseous materials, in concentrations having specific relationships to predefined thresholds, may create a potential for serious problems.
Thus, as a safety precaution, every situation wherein excessively low or excessively high concentrations of gases (such as oxygen) may exist, requires identification and evaluation of the specific concentration. For example, a long stretch of hallway with high pressure gas lines; a room with poor ventilation and significant amounts of inert or oxygen rich gas storage, or an environment having storage areas for chemicals which can deplete or enrich the oxygen concentration therein, provide potentially hazardous environments which should be monitored.
When an oxygen hazard may exist, there is needed a drift free, long life, accurate and dependable oxygen monitoring devices.
Oxygen concentration monitors are known in the prior art. For example, one such apparatus is disclosed in U.S. Pat. No. 5,402,665 to Hart et al., the contents of which are incorporated herein by reference.
However, the apparatus disclosed therein operates to compare ambient oxygen concentration with a predetermined threshold level and to provide an indication when the monitored concentration exceeds (or falls below) the threshold. More particularly a calibration gas, having an oxygen concentration equal to a desired threshold concentration level, is used to calibrate the device in order to account for variations in the operating characteristics of the oxygen sensor used therein. A specific testing and calibration procedure is thus required and the disclosed apparatus provides an indication if the monitored concentration is greater (or less) than the desired threshold.
The patent also discloses that one or more calibration gases may be used, at respective concentrations, in order to establish various calibration threshold levels.
However, a drawback of such a device is that a plurality of specific calibration procedures must be followed in order to calibrate the device to monitor concentrations with respect to a plurality of threshold levels to be monitored. Moreover, while the disclosed device may activate an audible alarm, buzzer, or LED (light emitting diode) to indicate a relationship between the concentration being monitored and a threshold, there is no provision for indicating the actual oxygen concentration level.
There is thus a need in the prior art for method and apparatus for monitoring concentrations of oxygen using only a single calibration gas.
DISCLOSURE OF INVENTION
It is accordingly an object of the present invention to provide a method and apparatus for monitoring concentration of oxygen using only a single calibration gas.
More specifically, it is an object of the invention to provide improved methods and apparatus for using a single calibration procedure, with a single calibration gas, for monitoring concentration of oxygen relative to a plurality of thresholds.
It is a particular object of the invention to provide an accurate display of the oxygen concentration level in a wide range of concentrations, following a single calibration procedure with a single calibration gas.
It is a more specific object of the invention to provide an oxygen concentration monitor, providing an indication of oxygen concentration relative to a plurality of thresholds, which requires only a single calibration procedure.
It should be appreciated, however, that while the disclosure refers specifically to monitoring of oxygen, the techniques described herein may be used for accurately sensing and monitoring concentrations of other gases.
In accordance with the invention, there is thus provided an oxygen monitoring apparatus which stores parameters descriptive of the operating characteristics of an oxygen sensor used therein for a calibration gas having a particular concentration, and which retrieves the parameters to determine the concentration of oxygen relative to any threshold concentration.
In accordance with another aspect of the invention, there is provided an oxygen monitoring apparatus which retrieves stored parameters descriptive of operating characteristics of an oxygen sensor and which uses the retrieved parameters in conjunction with other stored data to determine the concentration of oxygen being monitored.
In accordance with still another feature of the invention, there are provided a method and apparatus for identifying a monitored oxygen concentration level by determining a value necessary to compensate for characteristics of an oxygen sensor in a predetermined concentration of oxygen, by obtaining an output value from the sensor in an unknown concentration of oxygen, by modifying the output value to compensate for the sensor characteristics using the determined value, and by using the compensated value in conjunction with a table identifying expected sensor output values to identify the monitored concentration level.
These and other objects, features and advantages of the present invention will become readily apparent to those skilled in the art from the following description and drawings, wherein there is shown and described a preferred embodiment of the invention, simply by way of illustration and not of limitation of one of the best modes (and alternative embodiments) suited to carry out the invention. The invention itself is set forth in the claims appended hereto. As will be realized upon examination of the specification and drawings and from practice of the same, the present invention is capable of still other, different, embodiments and its several details are capable of modifications in various obvious aspects, all without departing from the scope of the invention as recited in the claims. Accordingly, the drawings and the descriptions provided herein are to be regarded as illustrative in nature and not as restrictive of the invention.
REFERENCES:
patent: 4189725 (1980-02-01), Rowland
patent: 4390869 (1983-06-01), Christen et al.
patent: 4464653 (1984-08-01), Winner
patent: 4779446 (1988-10-01), Rowland
patent: 4852384 (1989-08-01), Woolbert et al.
patent: 5198774 (1993-03-01), Williams, II et al.
patent: 5402665 (1995-04-01), Hart et al.
patent: 5423963 (1995-06-01), Fletcher et al.
patent: 5623105 (1997-04-01), Liston et al.
Litton Systems Inc.
Lowe Hauptman & Gilman & Berner LLP
Politzer Jay L.
Williams Hezron
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