Monitor for detecting hydrocarbons and other gases in an open area

摘要

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.