4.2. Power consumption and lifetime estimation
The heating voltage of 2.8 V is used to heat the sensor(s) up to 450◦C operational temperature.
The heating time for the sensors in the Wheatstone circuit is 1.3 s (see Fig. 10). The average constant current flowing through R4(see Fig. 2) during heating is 81 mA that results in 227 mW of power consumption in continuous measurement mode. Under these conditions and power supply specification provided in Section 3.1 the sensor node can support approximately(7.2 V × 15000 mAh/227 mW) = 475 h of continuous operation.
We estimate the battery lifetime for gas measurement once per 15 s. Since one measurement cycle is 1.3 s (excluding transmission, which takes place only in the case of emergency), the total estimated lifetime of the sensor node is(7.2 V × 15000 mAh)/(227 mW × 1.3/15 s) = 5490 h (228 days). A user can further increase the sensor node lifetime by making measurements once per 120 s as it is specified in Ref. [6]. In this case the lifetime will be theoretically around five years.