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2.5.5.4 Pellistor sensors
Pellistor sensors (or catalytic beads) are specically designed to sense explosive gases. The
detecting element consists of small “pellets” of catalyst loaded ceramic whose resistance changes in
the presence of gas.
2.5.5.5 Pellistor saver mode
While in saver mode and the subsequent stabilise time, the gas level displayed on the LCD screen
will indicate over range. If the alarm is so severe as to cause a sensor over-range the Gas-Pro
should have a gas test to ensure no lasting damage has occurred.
Pellistor sensors can suffer degradation if powered while exposed to ammable gas concentrations
of greater than 100% LEL, and also if exposed to high levels of H
2
S or silicones.
To reduce the degradation the instrument the Gas-Pro employs a Pellistor saver mode.
When the gas exceeds the saver threshold (user congurable: default 90%
– 95%) then the detector will turn off the sensor for a minimum period of 3
minutes 20 seconds.
After this time the sensor can be re-activated by a single click of the
operator button.
After a stabilisation time, if the gas level still exceeds the threshold then the
sensor will be turned off and the cycle starts again.
!
From the 1st November 2010, EN60079-29 part 1 has been harmonised under the ATEX
directive 94/9/EC. Therefore to comply with the ATEX directive, portable apparatus sensing
ammable gases should have a functional check with gas before each day of use (see Gas
testing and calibration on page 37). Other testing regimes may be employed depending on
local circumstances.
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