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a) CARBON MONOXIDE SENSOR. This is a sealed electrochemical cell
incorporating a long-life inboard filter. It consists of three or four platinum
electrodes in an electrolyte. Carbon monoxide gas diffuses through a tiny
hole on the face of the sensor. It reacts with oxygen present inside the cell to
form carbon dioxide. The reaction produces an electric current proportional
to the concentration of the gas. Sensor life is estimated at two years. Its
inboard disposable filter has an estimated life in excess of 200,000 PPM-
hours. An optional sensor includes an auxiliary electrode to remove cross
interference to hydrogen gas.
b) OXYGEN SENSOR. This 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. It takes about two years for this to
happen.
c) NITRIC OXIDE SENSOR. This is a sealed electrochemical cell
incorporating a disposable long-life inboard filter. It consists of three
exclusively noble metal electrodes in an electrolyte. Nitric oxide gas diffuses
through the tiny capillaries located on the face of the sensor. It reacts with
oxygen present inside the cell to form nitrogen dioxide. The reaction
produces an electric current proportional to the concentration of the gas.
Sensor life is estimated at two years. Its inboard disposable filter has an
estimated life in excess of 20,000 PPM-hours for NO
2
and 100,000 PPM-
hours for SO
2
.
This sensor requires a constant bias voltage for proper
operation. This voltage is supplied to the sensor, even when the instrument
is turned off. It draws a small amount of current and will drain the batteries
completely in about 10 months. For this reason the unit should always be
given a fresh charge once every 2-3 months.
d) SULFUR DIOXIDE SENSOR. This is an electrochemical cell similar to the
nitric oxide sensor. It has a range of 0 to 2000 PPM. Its life is estimated at
two years.
e) NITROGEN DIOXIDE SENSOR. This is an electrochemical cell similar to
the nitric oxide sensor. It has a range of 0 to 500 PPM. Its life is estimated at
two years.
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