Organic semiconductor vapor sensing method

This invention relates to vapor detection systems and particularly to methods and apparatus for temperature compensated vapor detection. An improved method and apparatus to automatically compensate for temperature variation in a vapor detection system is described. In one embodiment, two identical organic semiconductor film sensors in close thermal contact with each other are used in the feedback circuit of an inverting amplifier supplied by constant voltage. One of the sensors is isolated from vapor exposure to act as a reference for the other sensor which is used for vapor sampling. The output of the inverting amplifier provides an indication of the presence and relative concentration of vapor exposure. Variation in sample sensor resistance due to a change in temperature is accompanied by the same corresponding change in the reference sensor.