Commercial gas analyzers are not suited for long time usage and relatively too costly for
institutions in underdeveloped countries. Metal oxide sensors have emerged as simple and reliable
sensors for gases concentration measurements at an affordable cost. For gasification, carbon
monoxide, hydrogen and methane concentration must be monitored at the same time. Hence the
need for using three different gas sensors at the same time. SnO2 based sensor are of SnO2-based gas sensors have been broadly studied to take advantage of the variation of the resistance
of metal-oxides thin films. These sensors exhibit a resistor that depends on the nature of the gas
flowing between its pins and its concentration in the flue gas. SnO2-based gas sensors have a
special heating requirement that must be correctly addressed to have meaningful results. This
paper reports the methods used and the results obtained to fulfil that heating requirements for
three SnO2 sensors at the same time while avoiding power consumption peaks. Using the Pulse
Wide Modulation Technique, we have simultaneously synchronized the heating cycle requirements
of three MQ family SnO2-based sensors to estimate the concentration of carbon monoxide,
hydrogen and methane in synthetic gas produced by a wood-fired co-current downdraft gasifier.

Concentration; carbon monoxide; hydrogen; methane; pulse wide modulation.