12 • Description
GX-2009 Operator’s Manual
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. It prevents H
2
S in the ambient air from reaching the unit’s
combustible gas sensor. Removing H
2
S that is present in the monitored air prolongs the life of
the sensor. The H
2
S filter disk is dark red in color and although it may darken over time, its
color is not indicative of remaining filter life. The H
2
S filter disk can absorb H
2
S for 33 ppm
hours and should be replaced after that much exposure. With this many ppm hours of
absorption, the H
2
S filter disk should be replaced after 80 minutes of exposure to 25 ppm H
2
S.
This equates to replacing the H
2
S filter disk after 40 2-minute calibrations with a cylinder
containing 25 ppm H
2
S. If H
2
S exists in the monitoring environment, the H
2
S filter disk will
have to be replaced more frequently.
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.
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