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10.2 Sensor Limitations
The instrument is not suitable for use in ambient temperatures above 55°C and electrochemical toxic
gas sensors may be degraded, reducing life at these temperatures. Water should not be allowed to
collect on the sensors as this may impede gas diffusion. Use with care in wet or humid environments
where water may condense on the sensors, and check response after use.
Persistent exposure to high levels of toxic gas can shorten the life of toxic sensors. Toxic sensors
may also be cross-sensitive to gases other than their specic target gas, and hence the presence of
other gases may cause the sensor to respond. If unsure, contact Crowcon or your local agent.
Use of high power radio transmitters in close proximity to the instrument may exceed RFI immunity
levels and cause erroneous indications. If such problems are experienced, remove antennae to a
reasonable distance from the instrument (e.g. 30 cm).
Standard units detect ammable gases using a catalytic ammable sensor which operates in the
presence of oxygen. It is advisable to check the oxygen concentration as well as the ammable gas
concentration before entering a conned space. Oxygen levels below 10% will reduce a ammable
gas reading.
The performance of catalytic sensors may be permanently degraded if exposed to silicones, sulphur
containing gases (such as H
2
S), lead or chlorine compounds (including chlorinated hydrocarbons).
The performance of the PID sensor depends on the environment that is being measured. If
measuring high VOC concentrations where particulates are present in high concentrations check
calibration frequently and if the sensor has lost sensitivity, refer to the application note PID-AN-001
for maintenance instructions.
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