123 • Chapter 6: Maintenance GX-3R Pro Operator’s Manual
Replacing the Sensor Filters
CAUTION: The buzzer cover, sensors, filters, and alkaline batteries are the only user-
serviceable parts in the GX-3R Pro. Do not replace or modify any other part.
Combustible Gas Sensor Filter
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.
Dual CO/H
2
S Sensor Filter
The dual CO/H
2
S sensor has a half black/half white filter installed over it. The filter should be
replaced if you notice either 1) unexplained CO readings or 2) For users with a 1 ppm H
2
S alarm
point: a drift on the H
2
S channel’s zero reading, unexplained H
2
S readings, the filter appears dirty,
or every 6 months (whichever is sooner).
CO-Only Sensor Filter
A black charcoal filter is installed over CO-only sensors. The filter should be replaced if you
notice unexplained CO readings.
H
2
S-Only and PH
3
Sensors’ Filter
A white humidity filter is installed over H
2
S-only and PH
3
sensors. The filter absorbs humidity in
the sampling environment to prevent unstable readings around 0 ppm. “H2S” and “NH3” are
printed on the side of the filter.
•H
2
S: For users with a 1 ppm H
2
S alarm setpoint, the filter should be replaced if you
notice: a drift on the H
2
S channel’s zero reading, unexplained H
2
S readings, the filter
appears dirty, or every 6 months (whichever is sooner). For users with a 2 ppm or higher
H
2
S alarm setpoint, the filter does not necessarily ever need to be replaced.
•PH
3
: The filter should be replaced every 6 months.
NO
2
and SO
2
Sensors’ Filter
The H
2
S filter disk is tan in color. The filter should be replaced every 6 months.
HCN Sensor Filter
The H
2
S filter disk is dark gray in color. The filter should be replaced every 6 months.
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