The energy consumed by the sensor node for heating the sensitive layer is quite substantial. It is therefore important to minimize this component of the sensor node energy consumption. To find the best trade-off between sensitivity and power consumption, we have performed experiments to find the minimum temperature of the measurements for which the maximum sensor node sensitivity is not significantly affected.
The relationship between the sensor sensitivity and temperature can be assessed again by looking at the magnitude of the
voltage across the sensitive layer. In this case, we are interested in measuring relative data, which may be obtained by subtracting the magnitude of the voltage on the sensitive layer in the presence of methane from the magnitude of voltage in the air. Fig. 7b shows how the sensor relative response (or sensitivity) depends on the temperature of the sensor sensitive layer. One can see that the two curves for different methane concentrations in the air are close to each other, but do not coincide. This is due to the variation of the sensor sensitivity as a function of the gas concentrations. From the
diagram, it follows that the relative voltage on the sensitive layer in the presence of methane rapidly increases as the temperature changes from 100 ◦C to 500 ◦C and reaches its maximum between 500 and 550 ◦C. We have chosen 500 ◦C for our measurements.