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1. ELECTROCHEMICAL SENSORS
All electrochemical sensors are mounted on fitted socket fittings for easy installation and removal.
The electrochemical sensors are described below:
A. Nitrogen Dioxide sensor (NO
2
)
This is a three-electrode sensor that responds to nitrogen dioxide gas. Nitrogen dioxide is a “sticky”
gas and this sensor’s response is usually the slowest of all sensors.
B. Sulfur Dioxide sensor (SO
2
)
It is a three-electrode sensor that responds to sulfur dioxide gas. It is equipped with an inboard filter to
remove interference from H
2
S gas and other acidic gases.
C. Nitric Oxide sensor (NO sensor)
This is also a three-electrode sensor that responds to nitric oxide. It is equipped with an inboard filter
to remove any interference from other acidic gases.
The nitric oxide sensor requires a constant bias-voltage for proper operation. This is supplied by the
monitor’s battery. If the battery voltage drops below a certain value the monitor will turn off
automatically to maintain the sensor bias. If, however, the battery voltage further drops to near zero,
one must wait 24 hours after connecting the battery charger, for the sensor bias to recover.
D. Oxygen sensor (O
2
sensor)
This sensor measures the oxygen concentration in the sample. It is a two-electrode electrochemical cell.
It has a silver cathode and a lead anode. Oxygen diffuses through a tiny hole and reacts with the lead
anode. The reaction produces an electric current. The unit software linearizes the current vs. oxygen
response. The cell becomes exhausted when all the lead is consumed.
E. Hydrogen Sulfide sensor. (H
2
S)
This is a 4-series three-electrode micro sensor with low methanol interference. It measures the
concentration of hydrogen sulfide, which is a highly toxic gas. Special precautions must be taken during
calibration.
Summary of Contents for SI-AQ VOC
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