There are two common working principles for flue gas analyzers: electrochemical and infrared. Portable flue gas analyzers on the market usually combine these two principles. The following is an introduction to the working principles of these two types of flue gas analyzers:
Electrochemical Gas Sensor Working Principle: The gas to be measured, after dust removal and dehumidification, enters the sensor chamber and passes through a permeable membrane into the electrolytic cell. The gas diffused and absorbed in the electrolyte undergoes potentiostatic electrolysis at a specified oxidation potential. The gas concentration is determined based on the consumed electrolytic current.
A cylindrical cell made of plastic contains a working electrode, a counter electrode, and a reference electrode. The space between the electrodes is filled with electrolyte, and a porous PTFE membrane is sealed at the top. A preamplifier connects to the sensor electrodes, applying a certain potential between the electrodes to keep the sensor in operation. The gas undergoes oxidation or reduction reactions at the working electrode within the electrolyte, and reduction or oxidation reactions at the counter electrode. The equilibrium potential of the electrode changes, and this change is directly proportional to the gas concentration. It can measure gases such as SO2, NO, NO2, CO, and H2S, but the sensitivity of these gas sensors varies. The order of sensitivity from high to low is H2S, NO, NO2, SO2, and CO. The response time is generally a few seconds to tens of seconds, usually less than 1 minute; their lifespan varies, from as short as six months to as long as two or three years, while some CO sensors can last for several years.
Infrared Sensor Working Principle: This method utilizes the principle that different gases have specific absorption characteristics for electromagnetic wave energy at infrared wavelengths to analyze gas composition and content.
Infrared radiation generally refers to electromagnetic radiation with wavelengths ranging from 0.76 μm to 1000 μm. The infrared wavelengths actually used in infrared gas analyzers are approximately 1 to 50 μm.