THE ANALYTICAL RANGE OF TOXIC GASES OF COMBUSTION SOURCES IS TYPICALLY 30- 5000 PPM. WHY CANT I USE ONE SENSOR TO TAKE MEASUREMENTS OVER THIS RANGE?
Unlike analyzers using optical sensors that respond over many orders of magnitude, electrochemical sensors operate accurately over a much smaller range, typically one order of magnitude. These sensors are designed with a diffusion opening to admit the gas and respond to chemical reactions at the electrodes. If the gas concentration is relatively high for a given diffusion opening, the sensor electrodes saturate and do not respond linearly to the gas concentration. If on the other hand the gas concentration is too low for a given diffusion opening, sensor drift caused by temperature changes and residual interference by other gases become significant and reduce sensor accuracy. The proper optimum solution is to divide the entire analytical range into three ranges covering one order of magnitude each and for each sensor to determine the optimum diffusion opening for its operating range.
