US4778998A
Expired / Lapsed
US
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Humidity compensation for a photoionization type detector
Assignee: MSA Safety Inc
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Filing: 1987-06-05
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Granted: 1988-10-18
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Expires: 2007-06-05
Abstract
Abstract A photoionization type detector utilizes a photoionization sensor to detect the concentration of contaminants in the air, a humidity sensor to detect the water vapor concentration in the air and a temperature sensor to detect the temperature of the air. A microcomputer first calculates the water vapor concentration present in the air from the humidity and temperature sensor readings. Then, the microcomputer applies a predetermined correction factor corresponding to the calculated absolute humidity to the response of the photoionization sensor. This correction factor compensates for the negative cross-sensitivity of the photoionization sensor the humidity in the art and produces an accurate contaminant concentration level which is then displayed.
Inventors
- 👤 Byron L. Carnahan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 13:05
CPC Classifications
G; G01; G01N; G01N27/00; G01N27/62; G01N27/64; G01N27/66
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
128 words
A photoionization type detector with humidity compensation comprising: a photoionization sensor for detecting contaminants in the air and producing a signal proportional to the contaminants sensed; a humidity sensor for detecting the humidity in the air and producing a signal proportional to humidity sensed; a temperature sensor for detecting the temperature of the air and producing a signal proportional to the temperature sensed; a microcomputer connected to receive as inputs, the outputs of the photoionization sensor, humidity sensor and temperature sensor for calculating the humidity from which the microcomputer then chooses a predetermined correction factor and applies the correction factor to the photoionization sensor signal to compensate for negative cross sensitivity therein due to the humidity; and display means connected to the microcomputer for showing the compensated signal.
Claim 2
Dependent Claim
128 words
A photoionization type detector with humidity compensation comprising: a photoionization sensor for detecting contaminants in the air and producing a signal proportional to the contaminants sensed; a humidity sensor for detecting the humidity in the air and producing a signal proportional to humidity sensed; a temperature sensor for detecting the temperature of the air and producing a signal proportional to the temperature sensed; a microcomputer connected to receive as inputs, the outputs of the photoionization sensor, humidity sensor and temperature sensor for calculating the humidity from which the microcomputer then chooses a predetermined correction factor and applies the correction factor to the photoionization sensor signal to compensate for negative cross sensitivity therein due to the humidity; and display means connected to the microcomputer for showing the compensated signal.
Claim 3
Dependent Claim
28 words
An apparatus as described in claim 1 wherein the correction factor is 1.0e +0 .12×Pw where Pw is the partial pressure of water vapor in mm of mercury.
Claim 4
Dependent Claim
45 words
An apparatus as described in claim 2 wherein Pw=(H.sub.R /100* Ps, where H R is the relative humidity in % and is measured by the humidity sensor, and Ps is the partial pressure of wter in mm of mercury for complete saturation at temperature T.
Claim 5
Dependent Claim
39 words
An apparatus as described in claim 3 wherein Ps=10.sup.+[(8.1076-1750.3/(235+T)] where H R is the relative humidity in % and is measured by the humidity sensor, and T is the temperature in °C. and is measured by the temperature sensor.
Claim 6
Dependent Claim
25 words
An apparatus as described in claim 1 wherein there is a current-to-voltage convertor preamplifier electrically connected to and between the photoionization sensor and the microcomputer.
Claim 7
Dependent Claim
52 words
An apparatus as described in claim 2 wherein the microcomputer has a combination switch that allows either the compensated signal to pass to the display, or an uncompensated signal to pass to the display, and a function switch that has at least one range for looking at a certain contaminant concentration level.
Claim 8
Dependent Claim
25 words
An apparatus as described in claim 6 wherein the microcomputer applies the correction factor to the photoionization sensor signal by multiplying the correction factor thereto.
Claim 9
Independent Claim
86 words
A method for compensating the negative sensitivity due to humidity of a photoionization device comprising the steps of: detecting with a photoionization sensor the concentration of contaminants in the surrounding atmosphere; detecting the humidity and temperature in the surrounding atmosphere; calculating the absolute humidity of the surrounding atmosphere; determining a correction factor corresponding to the calculated absolute humidity to compensate for the negative sensitivity of the photoionization sensor; and applying the correction factor to the detected concentration of contaminants to achieve an accurate contaminant concentration level.
Claim 10
Independent Claim
86 words
A method for compensating the negative sensitivity due to humidity of a photoionization device comprising the steps of: detecting with a photoionization sensor the concentration of contaminants in the surrounding atmosphere; detecting the humidity and temperature in the surrounding atmosphere; calculating the absolute humidity of the surrounding atmosphere; determining a correction factor corresponding to the calculated absolute humidity to compensate for the negative sensitivity of the photoionization sensor; and applying the correction factor to the detected concentration of contaminants to achieve an accurate contaminant concentration level.
Claim 11
Dependent Claim
28 words
A method as described in claim 8 wherein the correction factor is 1.0e +0 .12×Pw where Pw is the partial pressure of water vapor in mm of mercury.
Claim 12
Dependent Claim
46 words
A method as described in claim 9 wherein Pw=(H.sub.R /100)×Ps, where H R is the relative humidity in % and is determined in the step of detecting humidity, and Ps is the partial pressure of water in mm of mercury for complete saturation at temperature T.
Claim 13
Dependent Claim
43 words
A method as described in claim 10 wherein Ps=10.sup.+[8.1076-1750.3/(235+T)] so Pw=H.sub.R /100*(10.sup.+[8.1076-1750.3/(235+T)] where H R is the relative humidity in %, and T is the temperature in °C. with H R and T being determined in the step of detecting humidity and temperature.
Claim 14
Dependent Claim
23 words
A method as described in claim 8 wherein the applying step includes the step of multiplying the detected concentration by the correction factor.
Claim 15
Dependent Claim
21 words
A method as described in claim 9 wherein the applying step includes the step of displaying the accurate contaminant concentration level
References Cited (Backward Citations)
US4429228A
Cited
US4698314A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-10-18 | 1992-04-18 | 1992-10-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-10-18 | 1996-04-18 | 1996-10-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-10-18 | 2000-04-18 | 2000-10-18 | $7700.00 | Window Closed / Lapsed |