Cross Sensitivity in CO Electrochemical Sensors

Exhaust Gas Measurement or Flue Gas Measurement is a sophisticated science and the demand for more accurate results are ever more important in the times where efficiency and cleaner environment becomes a requirement in the manufacturing/processing industry.

Sensors in the Flue Gas Analysers (FGA) are designed to measure a single gas. However, they may respond erroneously if they are not controlled or conditioned properly which in turn means that they will respond to other unintended gases which will result in inaccurate readings. This unintended response is known as sensor “cross-sensitivity”.

The introduction of Electrochemical (EC) sensors into the market is a widely accepted because they can be very accurate, portability and rugged stability that rival other measurement technology but with a low-cost solution. However, EC sensors are not immune to cross-sensitivity which require engineered solutions to mitigate.
 

The CO sensor responds to both CO and Hydrogen (H₂). Carbon Monoxide is type of gas which is commonly measured for any combustion application for tuning or environmental compliance. H₂ on the other hand is a combustion by-product of fuel degradation and is often found in combustion sources with low levels of oxygen in the exhaust. This means that in some combustion applications, H₂ concentrations can be quite high therefore resulting in CO readings to be artificially high. This is because standard CO sensors will react to the H₂ and add the output to the CO reading. This reaction to H₂ corresponds to up to 60 percent of the total H₂ ppm concentration in addition to whatever CO value that was measured.

An effective solution to this unique problem would be to use an engineered EC sensor that would measure H₂ and subsequently subtract that value from the combined CO + H₂ reading. By designing an additional electrode into an existing CO sensor and incorporating signal conditioning and logic to carry out the compensation, the CO reading will now be accurate even in varying presence of H₂ levels or with no H₂ in the exhaust gas.

Summary

H₂ is a cross-interfering gas that occurs during combustion process. The H₂ gas can influence the accuracy of CO reading equal to or greater than the actual CO. Compensation technologies exist that measure H₂ and subtract the effects from the CO reading to provide accurate readings are an effective solution to cross-sensitivity.