Testo Tech Notes: CO Sensor – H2 Cross Sensitivity
■Gas measurement is a sophisticated science, that done right, can provide very accurate results, or done wrong, can lead to costly misdirection. Sensors that are intended to measure single gases may respond erroneously if they are not controlled or conditioned properly. It is very pos-sible that a sensor may respond to that target gas and additionally respond to other gases as well. This unintended response is known as sensor “cross-sensitivity.”
■Electrochemical (EC) sensors are remarkably versatile and compact measuring devices that can be very accurate. EC analyzers off er low-cost precision, portability, and rugged stability that rival other measurement technologies when installed in a properly engineered and maintained analyzer. Like most other sensing technologies, however, EC sensors are not immune to cross-sensitivities which require engineered solutions to mitigate.
■An example of a common cross-interference to EC sensors occurs with the often used carbon monoxide (CO) sensors. CO sensors respond to both CO and hydrogen (H2). H2 is a combustion by-product of fuel degradation and is often found in combustion sources with low levels of oxygen in the exhaust. H2 is not a factor in ambient air, nor in many simple combustion sources, so it would therefore not pose a measurement problem. However, in some com-bustion applications, H2 concentrations can be quite high and if not accounted for, can cause the CO reading to be artifi cially 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 was measured.
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Please see the document for details |
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2019/9/25 |
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