6
To Display Oxygen with the "% Oxygen" Display (Models RGO-321, RGA-411/412,
RGA-611/612). Connect an appropriate probe to the dust and water-block filter and set the
selector switch to "% Oxygen". After warm-up, the display shows the ambient concentration of
oxygen in percent by volume. If ordinary air is being sampled, the display should read 20.9 ±0.2.
If it does not, switch to "AUTO ZERO", wait until the display shows "End", and return the
switch to the "% Oxygen" position.
• The "% Oxygen" display spans the range 0 to 40.0% with a resolution of 0.1%.
"Air-free" CO Flue Measurements
The RGA-411/412 and RGA-611/612 detectors can display measurements of CO on an
"air-free" basis if this feature is selected (see Section 10). When this selection is made, the
measured CO concentration is referred to air-free flue gas according to:
"Air-free" PPM CO =
20.9 measured % O
(measured ppm CO)
−
The instrument measures CO and % Oxygen and displays CO concentrations on an air-free basis
using the above relation. This calculation is used up to 16.0% Oxygen. If the oxygen
concentration is above 16.0%, measured values are displayed without conversion, i.e., the "air-
free" formula is not used.
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