Ampcontrol Pty Ltd
– ABN 28 000 915 542
GG2 DETECTOR USER MANUAL
GG2B011 Version 3
– June/19
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 14 of 39
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3.5.5 Operational Restrictions
Field bump tests and calibrations using portable gas applicators are susceptible to external air
velocities and pressurisation. These phenomena lead to incorrect concentrations of gas being applied
to the detector during calibration, which may result in under reporting the environmental concentration
of gas. The GG2 Calibration Cup and procedures detailed in this manual have been designed to
prevent errors in the calibration process. Use of any calibration cup not detailed in this manual is
prohibited.
3.6 Catalytic Sensors
3.6.1 Methane Gas Sensors
The Methane Gas Sensor, which operates on the catalytic combustible gas detection principle, is a
small platinum element coated in a catalyst. Electrical current is passed through the platinum wire and
the potential of the catalytic element is monitored by a simple Wheatstone Bridge arrangement.
Combustible gases, once in contact with the heated catalytic surface of the measuring element, react
and cause the surface temperature of the element to rise. Any increase in temperature affects the
resistance of the platinum wire, causing a small shift in potential across the Wheatstone Bridge
proportional to the concentration of the combustible gas. The GG2 Detector is temperature
compensated and provides a linear output.
3.6.2 Poisoning of Sensors (Contamination)
High levels of or long exposure to certain compounds may poison the catalytically active detector
filament thereby reducing or destroying its sensitivity.
Among these compounds are halides, sulphur compounds, leaded petrol, silanes, silicates and other
products with silicon. Products such as aerosol sprays, polishes, waxes and lubricants with silicones
and non-catalys
ed silicone rubbers such as “silastic”, phosphate esters and hydraulic fluids all damage
catalytic sensors.
CAUTION!
Some sensor poisons can cause irreversible damage to the sensor
rendering it unable to detect hazardous gas levels.
Table 3: Poisoning of Sensors
Chemical
Type
Common Examples
Products
Found in:
(Examples)
Effect on
Performance
Duration of
Effect,
PERMANENT POISONS
Silicones
Hexamethyldislioxane
(HMDS)
Dimethicone
Mould Release
Agents
Lubricants
Cosmetics
Cleaning
Products
Signal output on
gas is reduced.
Effect is noticeable
at levels above
2ppm
(continuous
exposure)
Permanent
Organo-
metallic
Compounds
Some Fuels
Petrochemical
Works
Signal output on
gas is reduced.
Effect is noticeable
Permanent
