Platinum resistive film CO sensor without selective layer

Response in resistance of platinum thin film sensors were studied in the presence of carbon monoxide under constant operating current. Both oscillatory and non-oscillatory changes in resistance were examined. Oscillations in resistances were found in the CO concentration range from 50 to 1000 ppm at operating temperatures between 80 and 150 °C. Both the amplitude and period increased with the increasing CO concentration. In non-oscillatory region, two different responses were observed, one of which the resistance of the sensor increased with increasing CO concentration and the other, resistance slightly decreased. It is believed that oscillations occurred between two branches of a Langmuir–Hinshelwood reaction mechanism. Above the upper branch of the oscillatory region, the resistance of the Pt films increases quasi linearly with the increase of CO concentration. Conversely, it decreases slightly below the lower branch.