Application of electrochemical gas sensor

How Electrochemical Gas Sensors Work

Electrochemical gas sensors typically consist of a working (i.e., sensing), counter, and reference electrode, all contained within a housing with a gas-permeable membrane. During sensing operation, it is submerged in electrolyte. Combined, these components allow it to perform its function.

The housing membrane allows gas (but not liquid) to enter the sensor. When the gas reaches the working electrode, an electrochemical reaction (oxidation or reduction, depending on the type of gas) occurs. This reaction initiates the flow of electrons (ie, current) between the working and counter electrodes. Oxidation reactions move electrons from the working electrode to the counter electrode, while reduction reactions move electrons from the counter electrode to the working electrode. In either case, the resulting current is proportional to the concentration of the target gas. This current is then amplified and processed according to the calibration to provide the user with a parts per million (PPM) or percent by volume reading. Most electrochemical sensors indicate a reading of zero if the target gas is not detected. However, unlike catalytic bead sensors, this sensor does require balancing or zeroing.

Although electrochemical sensors are designed to recognize specific gases, most exhibit some degree of cross-sensitivity. This phenomenon refers to the sensor's response to gases other than the target gas, usually due to higher chemical reactivity in the non-target gas than in the target gas. In some cases, non-target gases can mask the presence of target gases. For these reasons, it is important to use filters and bias voltages during operation to minimize the effect of cross-sensitivity on reading accuracy.

The rate of the chemical processes on which electrochemical sensors rely is directly proportional to temperature. Therefore, temperature changes can affect the sensing performance. For better reading accuracy over a wider range of environmental conditions, some form of temperature compensation is recommended.

Which gases do electrochemical sensors detect and measure?

Electrochemical sensors can detect and measure a wide variety of gases—from toxic to explosive to air quality—depending on application needs, including:

oxygen
carbon monoxide
nitrogen dioxide
Nitrogen oxides
sulfur dioxide