CO Electrochemical Sensor Detection Principle for Gas Detectors
The electrochemical carbon monoxide gas sensor is designed with a closed structure, which is composed of electrodes, filters, breathable membrane, electrolyte, electrode lead wires (pins), and housing.
Carbon monoxide gas sensor and alarm supporting the use of alarms, is the core of the alarm in the detection element, it is a fixed-potential electrolysis as the basic principle. When carbon monoxide diffuses into the gas sensor, its output terminal generates current output, which is provided to the sampling circuit in the alarm and plays the role of converting chemical energy into electrical energy. When the gas concentration changes, the output current of the gas sensor also changes proportionally, which is converted and amplified by the intermediate circuit of the alarm to drive different actuating devices to complete the detection and alarm functions such as acoustic, optical and electrical, which together with the corresponding control devices constitute an environmental detection or monitoring alarm system.
When carbon monoxide gas diffuses to the surface of the working electrode through the air holes on the shell via the permeable membrane, under the catalytic effect of the working electrode, carbon monoxide gas is oxidised on the working electrode. The chemical reaction formula is:
CO+H2O→CO2+2H++2e-
The H+ ions and electrons generated by the oxidation reaction on the working electrode are transferred to the counter electrode, which is kept at a certain interval from the working electrode, through the electrolyte, and the reduction reaction with the oxygen in the water occurs. The chemical reaction formula is:
1/2O2+2H++2e-→H2O
Thus, a reversible oxidation-reduction reaction occurs within the sensor. The chemical reaction equation is:
2CO+2O2 →2CO2
This reversible oxidation-reduction reaction always occurs between the working electrode and the counter electrode and produces a potential difference between the electrodes.
However, since the reaction at both electrodes polarises the electrodes, this makes it difficult to maintain a constant inter-electrode potential and therefore limits the range of carbon monoxide concentration that can be detected.
In order to maintain a constant interpolar potential, a reference electrode is added. In the three-electrode electrochemical gas sensor, its output reflects the potential change between the reference electrode and the working electrode, because the reference electrode does not participate in the oxidation or reduction reaction, so it can make the potential between the poles to maintain a constant (i.e., a constant potential), when the change in potential is directly related to the change in carbon monoxide concentration. When the gas sensor produces an output current, its magnitude is proportional to the concentration of the gas. By measuring the size of the sensor's output current with an external circuit through the electrode lead wire, the concentration of carbon monoxide can be detected, and there is a wide linear measurement range. In this way, by connecting a signal acquisition circuit and corresponding conversion and output circuits to the gas sensor, carbon monoxide gas can be detected and monitored.
