BT CGA-411 Operation Manual page 9

* The % GAS display spans the whole range of methane (0 to 100%) with the following
sensitivities:
Readings from 0 to 4.0%
Readings from 4.0 to 100% -
To Display Carbon Monoxide with the "PPM CO" Display. Connect an appropriate
probe to the dust and water-block filter and set the selector switch to "PPM CO". After warm-up,
the display shows the concentration of CO in parts per million (ppm) by volume. If the air is
clean (contains no carbon monoxide), the display should read zero. If it does not, switch to
"AUTO ZERO", wait until the display shows "End", and return the switch to the PPM CO
position.
* The "PPM CO" display spans the range 0 to 9999 ppm with a resolution of 1 ppm.
* The "PPM CO" display also displays hydrogen sulfide as described in Section 4.
To Display Oxygen with the "% Oxygen" Display. 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%.
C. Alarms
A detector alerts the user acoustically, with a sound alarm or beeper, and visually by
"flashing" the symbol(s) for the detected gas(es) whose concentration exceeds preset limits.
Visual alarms are displayed in-between readings for the particular display in use. For example, if
the display is showing readings for natural gas (switch at "% GAS") and the concentration of CO
rises above its alarm limit, the display will flash "CO", approximately every two seconds, in-
between displays of the concentration of natural gas. If the concentration of natural gas also rises
above its alarm limit, the display will show a reading, then "GAS", then a reading, then "CO",
and so on. Simultaneously, the acoustic alarm will be on.
Visual alarm symbols are "GAS" for natural gas, "CO" for carbon monoxide, "LoO2" for
low oxygen, and "HiO2" for high oxygen.
If a particular display is used to show concentration levels expected to be regularly above
the alarm limit, for example, the % GAS display when bar holing, the alarm for natural gas on
this display may be turned off. Similarly, if flue gas testing is done on a regular basis, the alarm
for CO on the PPM CO display may be turned off. Alarms on the % Oxygen display cannot
be turned off since this display is used for monitoring ambient air.
- Steps of 0.05%
Steps of 1.0%
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