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20
Sensor Limitations
The sensors used in the G-TECTA
®
4G have
limitations common to all gas sensors, and users
should be aware of the points listed below.
The Linde Group can advise on particular situations
and suggest alternative sensors if the instrument
is likely to experience extreme conditions.
G-TECTA
®
4G flammable instruments use a catalytic
pellistor gas sensor. Common with sensors of this
type, instrument readings will be unreliable over
concentrations of approximately 120% LEL and
oxygen is necessary for catalytic sensors to operate.
A ‘pellistor saver’ is used to disconnect power to
the pellistor sensor in the event of “over-range”
(above 100% LEL) to prevent burn out.
This feature “locks out” the sensor for 200
seconds, after which a press of the mode button
on the instrument will reconnect power to the
pellistor. Restart should be carried out in a known
clean air environment.
WARNING
 If the sensor power is reconnected
when the unit is exposed to an over-range gas
concentration there is a risk of damage to the
pellistor sensor.
WARNING
 Depleted oxygen levels can reduce
the flammable gas reading. If oxygen levels are
below safe breathing limits it should be assumed
that the flammable reading is low.
G-TECTA
®
Electrochemical gas sensors (toxic gases
or oxygen), contain chemicals. Extreme levels of
humidity can cause problems. The sensors are rated
for an (average) ambient humidity of 20-90% R.H.
However the sensors are commonly used from the
tropics, to deserts, to tundra without any functional
issues. Water should not be allowed to collect on
the sensor as this may impede gas diffusion.
Persistent exposure to high levels of toxic gas
will shorten the life of a toxic sensor. If the high
level gas is corrosive (e.g. hydrogen sulphide),
damage may occur over time to metal components.
Sensors may be cross sensitive to other gases.
If unsure, contact The Linde Group.
Available Sensors
Sensor Type Range
(LEL) Methane 0-100%
(LEL) Propane 0-100%
(LEL) Pentane 0-100%
(LEL) Butane 0-100%
(LEL) Ethylene 0-100%
(LEL) Hydrogen 0-100%
(LEL) Flammable alcohols,
ketones, general solvents
0-100%
(O
2
) Oxygen 0-25%
(O
3
) Ozone* 0-1 ppm
(CO) Carbon Monoxide 0-500 ppm
(H
2
S) Hydrogen Sulphide 0-100 ppm
(CO/H
2
S) Carbon Monoxide/
Hydrogen Sulphide
0-500ppm/0-100ppm
(SO
2
) Sulphur Dioxide 0-10 ppm
(NH
3
) Ammonia 0-100 ppm
(CO
2
) Carbon Dioxide
(non Ex areas)
0-5%
* Reactive gases – see G-TECTA
®
datasheet on gas sampling
with reactive gases