``The sensor requires application of a 1 second heating cycle which is used in connection with a circuit voltage cycle of 1 second. Each cycle is comprised by 4.8V being applied to the heater for the first 14ms, followed by 0V pulse for the remaining 986ms. The Vc cycle consists of 0V applied for 995ms, followed by 5.0V for 5ms. For achieving optimal sensing characteristics, the sensor's signal should be measured after the midpoint of the 5ms Vc pulse of 5.0V.'' 
Figure 3.9 shows this sensor.