Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Chemical analysis
Reexamination Certificate
1999-03-01
2001-09-11
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Chemical analysis
C436S164000, C340S632000, C250S343000, C204S401000, C073S023200
Reexamination Certificate
active
06289288
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates generally to the field of trace gas measurement and more particularly to a method of determination of actual gas values by storing and transmitting polynomials.
2. Description of Related Art
Remote gas sensor units are known in the art and can communicate measured gas concentration values over cables, powerline carrier, or RF systems back to a central location. However, various sensor types including heated metal oxide sensors have a tendency to drift and may require postprocessing to determine accurate gas concentrations. Therefore, if a remote unit simply reports a simple concentration determined by, say sensor resistance, the value reported may not be accurate.
Prior art systems containing remote sensors have typically reported either a derived gas concentration value based an empirical formula relating sensor resistance, or conductance, to concentration, or have just reported a raw resistance or conductance value back to a central location where a formula, or some empirical, method is used to compute gas concentration.
What is badly needed is a method of computing gas concentration values from measured sensor values in the presence of drift and variations caused by ambient temperature or humidity. In addition, the method should make it easy to perform such computations at the central location in systems where there are numerous remotes. The method must account for calibrated sensor and electronic conditions in each remote without putting an overwhelming computation burden on the remote.
SUMMARY OF THE INVENTION
The present invention relates to a method of determining remote gas concentration values from remote gas sensors. The method is particularly applicable to heated metal oxide sensors; however, it is not confined to that type of sensor and can be used with any remote gas sensor.
The method attempts to divide the computational load between the remote unit and a central unit with more computational power. The method can account for sensor drift, variations in remote electronics due to changes in ambient conditions such as temperature and humidity, and can make use of a central unit with tremendously more computational power than that of a remote which may contain only a minimum controller.
The method and apparatus of the present invention can fit local amplifier and electronics responses with polynomials to determine estimated sensor resistance (or some other sensor parameter such as conductance, capacitance, or inductance). The estimated sensor output value can then be transmitted to a central unit for processing where it can be corrected for local temperature and humidity at the remote unit (if the remote unit also transmits such data), and then the received value can be used as part of a statistical process to estimate what the correct current zero point of the sensor should be. A corrected output value can be derived, and used to get actual gas concentration by a system of fitted polynomials for the sensor that were generated during calibration. Since each remote has different calibration polynomials, they can be stored in the remote. The present invention provides a way that each remote can store and transmit the coefficients of its calibration polynomials, when requested, to the central unit. The method provides a way of storing and transmitting polynomial coefficients of any sign or order of magnitude in fixed length words without the normal scaling problems.
REFERENCES:
patent: 5464982 (1995-11-01), Drucker et al.
patent: 5667651 (1997-09-01), Bryan
patent: 6037592 (2000-03-01), Sunshine et al.
patent: 6096560 (2000-08-01), Scripca et al.
patent: 6169488 (2001-01-01), Ketler
patent: 6182497 (2001-02-01), Krajci
Chelsea Group LTD
Duong Khoi
Hoff Marc S.
Kraft Clifford
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