Changes in composition of the electrolyte will result in measurable current change between the working electrode and return electrode. ▪ Electrolyte is encapsulated in a casing ▪ Gas permeates through a hydrophobic membrane ▪ Voltage is supplied to the working electrodes. ▪ In the absence of the target gas a negligible current flows through the sensor to provide the baseline zero. When target gas is present the oxidization of the gas produces or consumes electrons that facilitate higher charge transport (current).