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"Air-free" CO Flue Measurements. Flue gas measurements of CO can be displayed on
an "air-free" basis if this feature is selected (see Section 11). When this selection is made, the
measured CO concentration is referred to air-free flue gas according to:
"Air-free" PPM CO
The instrument measures CO and % Oxygen and displays CO concentrations on an air-free basis
using the above relation.
concentration is above 16.0%, measured values are displayed without conversion, i.e., the "air-
free" formula is not used.
E.
Hydrogen Sulfide Detection
The electrochemical cell used to detect CO also responds quantitatively to hydrogen
sulfide (H
S). The response to 1 ppm H
2
holds for all values of H
the PPM CO display, 50 ppm H
will register as 400 on the PPM CO display. The CGA-411 and CGA-412 detectors thus monitor
ambient levels of hydrogen sulfide, as well as CO, and will alarm if the H
above one quarter of the limit set for the CO alarm. In particular, when the % Oxygen display is
selected, a detector will alarm at 9 ppm H
limit for CO).
The response of the electrochemical cell to H
unit is calibrated with CO. No separate calibration with H
If an atmosphere contains both CO and H
is, the reading on the PPM CO display includes both the response to CO and to H
for CO only is needed or desired, the flue gas probe and its attached filter can be used for
sampling ambient air. The filter removes H
concentration.
WARNING:
A detector will not respond to H
the flue gas probe and filter.
=
20.9 measured % O 2
This calculation is used up to 16.0% Oxygen.
S is registered as 4 on the PPM CO display. This ratio
2
S up to about 1000 ppm H
2
S will register as 200 on the PPM CO display and 100 ppm H
2
S (approximately one quarter of the 35 ppm alarm
2
20.9
(measured ppm CO)
−
S. Thus, 10 ppm H
2
S is automatically calibrated whenever the
2
S is required.
2
S, the response of the detector is additive, that
2
S and the reading then corresponds to the CO
2
S when the sampled gas is drawn through
2
11
If the oxygen
S will register as 40 on
2
S concentration rises
2
S. If a reading
2
S
2
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