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19
UK
Sensor Limitations
The sensors used in the G-TECTA
®
SG 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
®
SG 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 15-90% 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) Flammable alcohols,
ketones, general solvents
0-100%
(O
2
) Oxygen 0-25%
(O
3
) Ozone* 0-1 ppm
(CO) Carbon Monoxide 0-500 ppm
(CO) extended range
Carbon Monoxide 0-1500 ppm
(H
2
S) Hydrogen Sulphide 0-100 ppm
(H
2
S) extended range
Hydrogen Sulphide
0-500 ppm
(SO
2
) Sulphur Dioxide 0-10 ppm
(NO
2
) Nitrogen Dioxide* 0-10 ppm
(H
2
) Hydrogen 0-1000 ppm
(PH
3
) Phosphine* 0-5 ppm
(Cl
2
) Chlorine* 0-20 ppm
(HF) Hydrogen Fluoride* 0-10 ppm
(F
2
) Fluorine* 0-1 ppm
(COCl
2
) Phosgene* 0-1 ppm
(ClO
2
) Chlorine Dioxide 0-1 ppm
(NH
3
) Ammonia 0-100 ppm
(NH
3
) extended range
Ammonia
0-1000 ppm
(HCN) Hydrogen Cyanide 0-25 ppm
(NO) Nitric Oxide 0-100 ppm
(ETO) Ethylene Oxide 0-10 ppm
(CO
2
) Carbon Dioxide
(non Ex areas)
0-5%
* Reactive gases – see G-TECTA
®
datasheet on gas
sampling with reactive gases