RKI Instruments Gas Tracer - Manual (Page 41)

Gas Tracer Operator’s Manual Measuring Mode, Normal Operation • 33
Applications with High Levels of Combustible Gas
The Gas Tracer 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 Gas Tracer 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 46 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 Gas Tracer 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.
%LEL Sensor Relative Responses
Although the standard factory setup and calibration for the combustible gas
channel is to methane (CH
4
), the combustible sensors will respond to other
combustible gases as well.
The table below lists the conversion factors for several hydrocarbon gases for
the % LEL combustible sensor if it is calibrated to methane. Conversion
factors are not available for the % volume TC sensor. To use this table,
multiply the display reading on the combustible gas channel by the factor in
the appropriate row to obtain the actual gas concentration. For example, if