Det-Tronics 505 Combustible Gas Detector Transmitter with Combustible Gas Sensor CGS - Manual (Page 6)

3 95-8472 3.1
A brief exposure to any of these materials may temporarily
increase the sensitivity of the sensor due to etching of the
catalytic surface. This practice is not recommended,
since it is unreliable and may give a false sense of
security.
Exposure to high concentrations of gas for extended
periods can introduce stress to the sensing element and
seriously affect its performance. After exposure to a high
concentration of combustible gas, re-calibration should
be performed and, if necessary, the sensor should be
replaced.
The degree of damage to a catalytic sensor is determined
by the type of contaminant, its concentration in the
atmosphere, and the length of time the sensor is exposed.
When a sensor has been exposed to a contaminant or to
a high level of combustible gas, it should be re-calibrated
at the time, followed by an additional calibration a few
days later to determine whether a significant shift in
sensitivity has occurred.
0 90 5 10 15 20 30 40 50 60 70 80 100
180
160
140
120
100
80
60
40
20
0
CONTROLLER
DISPLAY
READING
(%LFL)
PERCENT OF METHANE (BY VOLUME)
LOWER FLAMMABLE LIMIT
(100% LFL)
UPPER FLAMMABLE LIMIT
C1125
Figure 2—Typical Response of a Catalytic Sensor over a Range of 0 to 100% Methane by Volume
0 90 5 10 15 20 30 40 50 60 70 80 100
100
90
80
70
60
50
40
30
20
10
0
CONTROLLER
DISPLAY
READING
(%LFL)
PERCENT OF OXYGEN IN MIXTURE (BY VOLUME) B1126
50% LFL METHANE IN STANDARD AIR
4.5% METHANE
2.5% METHANE
90% LFL METHANE IN STANDARD AIR
Figure 3—Effect of Oxygen Enriched and Deficient Atmospheres