AMBIENT-TEMPERATURE DEPENDENT HEATING POWER-CONTROL FOR MOTOROLA MICRO CO GAS SENSOR

Gas sensors suffer from stability and reproducibility. In this paper, a new method of driving micro gas sensors to get reproducible behaviou r under different ambient conditions is proposed. The new method consi sts of a proportional pattern of temperature modulation with alternati ng high and low power-heating pulses depending upon the effect of ambi ent temperature on sensing conductance of the micro gas sensor. The se nsor conductance was very sensitive;to changes in ambient temperature and was almost insensitive to changes in relative humidity in the work ing range of 50 to 95%. The sensor exhibited a reproducible CO gas res ponse with sequential pulse technique and the measured conductance at the end of a low power pulse varied linearly with the square root of c oncentration of CO gas up to 400 ppm. With the correct proportional po wer control, the sensor exhibited drift free, reproducible and almost constant CO gas response characteristics over the normal working tempe rature range of 25 to 40 degrees C.