RKI Instruments GX-2009 Manual - Manual (Page 12)

7 • Description GX-2009 Operator’s Manual
sensor will respond if exposed to H
2
S and certain hydrocarbon gasses.
The charcoal filter scrubs these gasses out of the gas sampled to avoid
false CO readings. The H
2
S absorbing material added to the charcoal filter
extends it’s H
2
S absorbing life. If false CO readings are noticed, especially
high readings in the presence of H
2
S, change the charcoal filter disk.
H
2
S Removal Filter Disks
One H
2
S removal filter disk is located in a recessed area of the
combustible gas sensor diffusion port in the sensor retainer. The H
2
S
removal filter disk is white when new. It scrubs H
2
S out of the gas sampled
to increase the life of the combustible sensor. It darkens as it absorbs H
2
S
and must be changed when it turns to a dark brown color. The
recommended replacement frequency will depend on how often the unit is
exposed to H
2
S and the concentration. Check the condition of the H
2
S
removal filter disk quarterly.
Sensor Cover
The sensor cover is white and protects the scrubber filters and sensors
from dust and water. It fits on the sensor retainer gasket over all the sensor
diffusion ports and is secured in place by the sensor cover retainer. If the
sensor cover becomes dirty, the response time and accuracy of the GX-
2009 will be affected. Replace the sensor cover if it appears dirty.
Sensors
The GX-2009 uses four sensors to monitor combustible gases, O
2
, CO,
and H
2
S simultaneously. The sensors are protected from the environment
by the sensor cover which allows ambient air to diffuse to the sensors. The
sensors use different detection principles, as described below.
Combustible Gas (LEL) Sensor
The combustible gas sensor detects combustible gas and vapors in the
LEL (lower explosive limit) range with a catalytic element. A sintered metal
flame arrestor covers the element and allows ambient air to diffuse into the
sensor. The reaction of gas with oxygen on the catalyst causes a change in
the resistance of the element which affects the current flowing through it.
The current is amplified by the GX-2009’s circuitry, converted to a
measurement of combustible gas concentration, and displayed on the
LCD.
CAUTION: Do not expose the combustible sensor to high concentrations
of combustible gas such as that from a butane lighter.
Exposure to high concentrations of combustible gas may
adversely affect the performance of the sensor.