4.3. Actuation time estimation
In this section we estimate the wireless sensor–actuator system actuation time necessary to react on a gas leak. For correct time estimation we synchronize both the sensor node and the actuator with computer.
In this experiment we install the sensor node in gas chamber and emulate the gas leak by using 2% CH4. Sensor node is programmed for environmental scanning every 15 s. This interval is a viable trade-off between the long time operation of wireless sensor node and safety requirements for combustible gas detection. The sensing takes 1.3 s. Time required to send a request from the wireless sensor node to the wireless actuator is 0.1 s. The response of actuator includes the time for node request receiving and processing (0.1 s)and the time of valve closing (50 ms). Therefore, the total time of system reaction on gas leak is less than 17 s.
In parallel, the sensor node can send an alert message to a WSN operator and/or inform an appropriate civil service to put in place the necessary remedial measures. This alerting, however, is out of scope of this work.