GX-2012 Operator’s Manual
Measuring Mode, Normal Operation • 33
Combustible Gas Detection
The GX-2012 can support two combustible gas sensors, a TC (thermal conductivity)
sensor for detection in the % volume range, and a catalytic sensor for detection in the %
LEL range. Either or both sensors may be installed in your unit.
If both the % volume and % LEL sensors are installed, the combustible gas channel is
setup at the factory as % LEL/% volume autoranging. In this case, the combustible gas
channel will display the combustible gas concentration in % LEL up to 100% LEL. If the
combustible gas concentration rises above 100% LEL, then the unit automatically begins
displaying the concentration in % volume.
CAUTION:
If both combustible sensors are installed in your instrument, make sure you
follow the recommendations in the next section, “Applications with High
Levels of Combustible Gas” on page 33, to protect the % LEL sensor.
Failure to do so will result in damage to the % LEL sensor.
WARNING:
If the combustible channel is set for % volume only, then there are no
gas alarms for any detection channel. See “HC Range Screen” on
page 44.
There are three important issues to keep in mind when monitoring for combustible
gas.
Applications with High Levels of Combustible Gas
The GX-2012 provides the % LEL sensor with some protection by turning off the % LEL
sensor power temporarily when it determines that a % LEL over scale (more than 100%
LEL) concentration of combustible gas is present. When this happens, “OVER” is
displayed below the gas list and the display units to the right of the combustible gas
channel change to % volume. However, this protection is not adequate to completely
prevent damage to the sensor when it is exposed to moderate or high levels of % volume
gas.
Combustible gas is present at moderate or high % volume levels in many applications
such as purging applications. If your GX-2012 is equipped with both the % LEL and
%volume sensors, you must set up the instrument so that the combustible channel operates
in the %volume only range when you use the instrument for this type of application to
protect the % LEL sensor from damage. You can set the combustible channel to operate in
the % volume range only in the HC Range Screen of Display Mode. See “HC Range
Screen” on page 44 for instructions to set the combustible channel to operate in the %
volume range only.
CAUTION:
Failure to set the combustible channel to % volume only operation when
using the GX-2012 for applications with moderate to high % volume levels
of combustible gas will result in damage to the % LEL sensor.
The instrument may be set up for combustible channel autoranging operation when it is
used for confined space applications where % volume combustible gas concentrations are
not likely to be found.
Silicone & Other Potentially Damaging Compounds
Silicone vapors and chlorine and fluorine compounds, such as chlorinated hydrocarbons,
can damage the %LEL sensor. These compounds should be avoided. If exposure to these
compounds is suspected, verify the %LEL response on a known gas sample.
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