3. System and component architecture
In this section we will analyze the individual components of
the gas detection system in more details, focusing on the design
choices.
3.1. Sensor and relay nodes
The hazardous gas concentration can be measured using optical,
catalytic and semiconducting gas sensors [16]. The major problem
associated with the measurement of combustible gas concentration
in autonomous devices is the high power consumption associated
with the sensors. In this work, we have used a 2D semiconductor gas
sensor produced on an aluminum membrane [13]. This type of sensor
is characterized by high sensitivity, long lifetime and relatively
low energy consumption (see Table 1 ‘2D semiconductor sensor’).
Besides, the sensor has an ExsIU/ExdIIB+H2U degree of implosion
protection (see the protection requirements in [17]), which makes
it safe to use in a hazardous environment. The system works by
heating the sensitive layer of the sensor to a temperature of around
500 ◦C, and then measuring the conductivity of the semiconductor,
which is affected by the gas concentration. Typical applications [11]
use a continuous measurement mode in which the semiconductor
is kept at a constant temperature. In our system, instead, to further
decrease the energy consumption [18], the sensitive layer is only
heated when measurements are required, which occurs at regular
intervals, i.e., we replaced the continuous measurement mode with
the pulse of a PWM signal implementing a duty-cycle mode [19].