The basic elements of an electrochemical sensor are: a working (or sensing) electrode, a plate, and usually a reference electrode. The aforementioned electrodes are attached to a sensor box lined with a liquid electrolyte. The working electrode is located on the inside of a Teflon membrane, which is porous for air flow but impermeable to the electrolyte.
The gas diffuses into the sensor and travels through the membrane to the electrodes. When the gas reaches the electrodes, an electrochemical reaction occurs—either oxidation or compression, depending on the type of gas. For example, carbon monoxide may be oxidized to carbon dioxide; oxygen may be compressed to water. Oxidation reactions flow electrons from the working electrode to the plate through an external circuit; conversely, compression reactions flow electrons from the plate to the working electrode. The above electron flow constitutes the current and is proportional to the gas concentration. Electronics within the instrument sense and amplify the current according to the calibration and measure the output. The instrument then displays the gas concentration to the toxic gas sensor, such as: the toxic gas sensor displays the concentration in parts per million (PPM), and the oxygen sensor displays the concentration in percent.
