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What is Dual-Sensor Technology?

The FGA900 series of compact continuous emissions monitoring systems (CEMS) is an integrated solution for flue gas measurements in smaller combustion processes. 

It provides accurate, reliable concentrations of carbon monoxide, nitric oxide and oxygen in flue gases from gas- and biomass-fired boilers and furnaces. It also calculates values for combustion efficiency as well as the concentrations of NOx and carbon dioxide. This information allows better process control, which lowers fuel costs and keeps emissions within compliance levels.

Dual Sensor Technology
FGA900 series uses a proprietary measuring technique, Dual Sensor technology, which allows it to make measurements that are sensitive, reliable and stable. Each sensor module uses a pair of electrochemical cells that are sensitive to the target species, so the FGA instrument may have one, two or three modules.

The cells in each pair are used alternately, with the switching sequence managed by the instrument’s microprocessor, so that a continuous uninterrupted output is produced. Figure 1 shows how this works. 

What is Dual-Sensor Technology?

The outputs from the two cells in a pair are shown as Channel A (red) and Channel B (blue). At first, Channel A is measuring the sample gas and Channel B is exposed to air. After 25 minutes, the instrument records the zero reading of Channel B and exposes it to the flue gas sample. The reading is allowed to settle for 5 minutes, after which the gas concentration readings of the two sensors are compared. The instrument indicates an error if there is a significant difference between the gas concentrations. This is usually an indication that the instrument is overdue for calibration, but it can also be a warning that one of the sensors is nearing the end of its life. The instrument then uses the Channel B sensor for gas measurements and exposes the Channel A sensor to air for 25 minutes, and the sequence repeats.

Dual Sensor Technology allows an analyzer employing electrochemical sensors to achieve high levels of accuracy and reliability by ensuring the sensors have time to recover from exposure to any contaminants in the flue gas which could cause poisoning, and to rehydrate after exposure to a moisture-free sample.

The quality and effectiveness of the technique allow the FGA900 series to achieve QAL1 approval for measurements of CO, O2 and NO according to the EN 15267 standard.


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