초록 ▼

An improved area monitor for detecting gas concentration is provided that requires a very infrequent calibration, and works reliably in detecting a particular target gas using only two semiconductor sensors. One of these sensors will exhibit a drift that is constantly monitored and automatically com

An improved area monitor for detecting gas concentration is provided that requires a very infrequent calibration, and works reliably in detecting a particular target gas using only two semiconductor sensors. One of these sensors will exhibit a drift that is constantly monitored and automatically compensated for, while the other sensor exhibits a stable, repeatable response over very long periods of time. Once the "stable" has been initially calibrated, the concentration of the target gas can be discerned directly from the resistance of this sensor, although more that one particular chemical gas may cause the stable sensor to change resistance. The second sensor is then used to discern whether or not the change in resistance of the stable sensor was due to the actual target chemical, or due to some other similar chemical. The second sensor is selected to be of a type that responds in one direction (i.e., its change in resistance either increases or decreases) when emersed in the particular target chemical of interest. For all other similar gases, the resistance of the second sensor will change in the opposite direction.

대표청구항 ▼

[ We claim:] [1.] An area monitor for detecting a gaseous compound, comprising:(a) a first sensor that exhibits a physical parameter that responds to variations in concentration of a pre-determined target gas within an area of detection, said first sensor's physical parameter being substantially rep

[ We claim:] [1.] An area monitor for detecting a gaseous compound, comprising:(a) a first sensor that exhibits a physical parameter that responds to variations in concentration of a pre-determined target gas within an area of detection, said first sensor's physical parameter being substantially repeatable at various concentrations of said target gas, said first sensor's physical parameter being substantially stable over long periods of time;(b) a second sensor that exhibits a physical parameter that responds to variations in concentration of said pre-determined target gas within said area of detection, said second sensor's physical parameter changing in one direction when in the presence of said target gas, said second sensor's physical parameter changing in the opposite direction when in the presence of a gas other than the target gas that becomes introduced into said area of detection; and(c) a monitoring system that interfaces with said first and second sensors, said monitoring system detecting the physical parameter of said first sensor and creating an output signal that varies with respect to the concentration of said target gas, said monitoring system having a clock circuit that, at pre-determined time intervals, repeatedly detects the physical parameter of said second sensor and, if the concentration of the target gas as determined by the physical parameter of said first sensor is below a pre-determined threshold value, re-calibrates said second sensor at each pre-determined time interval, thereby automatically compensating for any drift over time in the physical parameter value of said second sensor.