FLAMMABLE GAS SENSOR/TRANSMITTER
A T E X
M1
GROUP I & II
INTRINSICALLY
SAFE
5 INSTALLATION
continued
5.12 High Concentrations of Flammable Gas
Exposure of low concentration catalytic combustion sensors to concentrations of
flammable gas greater than the LEL can affect the sensitivity and zero stability of
catalytic elements and the calibration should be checked after such an exposure.
If the gas concentration does exceed 100% LEL, the supply voltage to
the catalytic combustion sensing element will be automatically switched
off to prevent damage to the element.
The sensor output signal will be CLAMPED, the display will indicate
OVERRANGE and the STATUS indicator will FLASH.
Refer to Sections
7, 8.5 & 8.6
5.13 Toxicity
Be aware that most flammable gases and vapours are also toxic at low
concentrations of LEL.
5.14 New Installations
Flammable gas sensors based on pellistor technology require regular zero and
span check and adjustment operations to ensure that they remain accurate.
The pellistor device ages during its lifetime and its baseline and sensitivity
characteristics will change. These operations are normally performed three weekly.
The pellistors baseline tends to move positively throughout its lifetime. In the early stages
of the lifetime, the baseline tends to move positively at a relatively fast rate.
This movement slows down with age. Users may note a small positive reading
from the gas sensor during the first month or so of usage.
The pellistor fitted to the TX6383 will have a baseline change equivalent of upto 2.5%
LEL (0.11% v/v) in its first month of usage, then a further 1.5% LEL
(0.066% v/v) in the second month.
For newly installed equipment, end users should consider performing a zero offset
adjustment every fortnight for the first two months. This will ensure that the offset
movement is kept below 2% LEL (0.088% v/v) during the ‘settling in’ period.
Refer to Section
8
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INSTALLATION & OPERATING DATA
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ISSUE S 01/15
