Understanding the JXCT Electrochemical Gas Sensor Circuit
Electrochemical gas sensor measures the concentration of a target gas by using oxidation or reduction reactions to generate positive or negative current flow through an external circuit. The basic components of an electrochemical sensor include a “working” electrode, a “counter” electrode and in most case a “reference” electrode. These components are combined inside the sensor housing with a liquid electrolyte. The top of the sensor has a membrane and diffusion limiting orifice through which ambient air interacts with the sensor’s electrolyte.
How Do Electrochemical Gas Sensors Work?
As gas diffuses through the membrane and comes in contact with the electrolyte, an electrochemical reaction occurs. An oxidation reaction results in current flow from the working electrode to the counter electrode, while a reduction reaction results in current flow in the opposite direction. The magnitude of this current flow is proportional to the amount of gas present and is measured by an external electrochemical gas sensor circuit. This current is amplified, filtered and processed to obtain a calibrated reading in engineering units. Most electrochemical sensors output zero current when no target gas is present, and unlike catalytic bead sensors do not need a balance or zero adjustment.
An electrochemical gas sensor is available for just about any target gas, and across a wide range of sensitivities, such as a highly accurate electrochemical CO sensor. Although they are designed to be as specific as possible, most electrochemical sensors will respond in some manner to gases other than the target gas. This is called cross-sensitivity and is a result of the sensor’s electrolyte reacting with gases that are more chemically active than the target gas. In some cases, certain gases can even cause a reverse reaction in the sensor chemistry that can mask the presence of the target gas. The use of filters and bias voltage applied to the sensor during operation can reduce the effect of cross-sensitivity.
Since electrochemical gas sensors depend on chemical processes whose rates are proportional to temperature, the output of most electrochemical sensors will vary with temperature, and some form of temperature compensation is recommended if the sensor is to provide reliable readings over a wide range of ambient conditions.