33 • Chapter 3: Operation GX-3R Pro Operator’s Manual
Overscale Protection
The GX-3R Pro protects the combustible gas sensor by temporarily turning off the sensor power if
levels exceeding 100% LEL are detected. Nevertheless, combustible gas concentrations above
100% LEL can still affect the zero level or calibration of the combustible gas sensor.
CAUTION: Do not expose the combustible gas 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.
CAUTION: Any rapid increase in the combustible gas reading on the combustible gas channel
followed by a declining or erratic reading may indicate a gas concentration above
the LEL which may be hazardous.
Damaging Gases
Some gases such as silicone vapors, chlorinated hydrocarbons, and sulphur compounds can
contaminate the sensor’s detection elements. This causes sensor damage and/or a reduced
response to combustible gas. Make every effort to avoid these gases.
The H
2
S scrubber disks protect the combustible sensor from H
2
S, but you should avoid other
sulphur compounds.
LIMITED HC GAS LIST Alarm
An HC GAS LIST LIMITED alarm can occur at startup or after a calibration.
The combustible gas sensor actually contains 2 separate sensors: a standard catalytic sensor and a
backup, poison-resistant sensor that is resistant to sensor poisons like silicone. A LIMITED HC
GAS LIST alarm indicates that the standard sensor has a reduced output, possibly due to one or
more sensor poisons in the environment, and that the poison-resistant sensor is being used to
provide gas readings. The poison-resistant sensor has a limited list of detectable gases. The table
shown on page 48 shows which gases can and cannot be detected after receiving a LIMITED HC
GAS LIST alarm.
If your application requires detection of a gas still detectable after a LIMITED HC GAS LIST
alarm (like methane or isobutane), there is no need to replace the combustible gas sensor
.
However, if your application requires detection of a gas not detectable after a LIMITED HC GAS
LIST alarm (like methanol or ethanol), you must replace the combustible gas sensor as soon as
possible.
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