4.1. Network routine operation
In the case of routine operation, when hazardous gas concentration
is not detected or is below 0.15% the sensor node goes to sleep
mode. The measured values of gas concentration are not transmitted
to the network coordinator (marked with the letter ‘C’ in Fig. 6),
but can be saved in a memory chip onboard. However, while the sensor node performs the measurements, the relay nodes (marked
with the letter ‘R’ in Fig. 6), the network coordinator and the wireless
actuator (marked with the letter ‘A’ in Fig. 6) must be operated
in receive mode all the time. In accordance with the ZigBee protocol,
the sensor node acts as a remote terminal. As data transmission is
only performed when the preset events occur, most of the time the
ZigBee ETRX2 module is in sleep mode and its energy consumption
is insignificant [23].