The SST Model GC800 series of Combustible Gas Sensors are used to determine the concentration of gas accumulated in a protected area and transmit this information to a central control point. The SST sensors use the “catalytic” method of gas detection. Located inside a stainless steel flameproof housing, the sensing element is exposed to the detected gas through a sintered stainless steel flame arrestor. The actual detector consists of a matched pair of elements, each consisting of a fine platinum wire embedded in a bead of alumina material. Flammable gases in low concentrations will not burn by themselves, but when in contact with a suitable catalyst, it is possible to burn (or oxidize) any concentration of gas. One of the element pairs in the SST sensor is treated with such a catalyst, while the other element is protected with a similar, non-catalytic material. The platinum wires within the elements are heated by passing a suitable current through them. When the gas is oxidized on the surface of the catalyst, additional heat is released, which causes a temperature rise on the catalytic surface. This change in temperature is measured and converted to determine the amount of gas present.
The SST Combustible Gas Sensor has been designated with a special “poison-resistant” sensing material, and provides accurate measurements in atmospheres where traces of silicone or other poisoning agents may be present. Readings are unaffected by humidity or carbon dioxide. The concentration of combustible gas is measured in terms of the Lower Explosive Limit (LEL).
The Model GC800 Combustible Gas Sensor requires an electronic “transmitter”, which may be installed in the associated explosion proof junction box, or located at the control monitoring point. This transmitter converts the signal from the catalytic element to a standard 4-20 mA signal. This signal may be connected to a suitable SST NOVA-5000 Gas Detection Module, or to any other device with a standard 4-20 mA input. Connections to the combustible gas are normally made with 3 conductor shielded cable. The Model GC800 is suitable for the most demanding applications. A large body mass ensures excellent vibration characteristics when used in large machinery applications. Corrosion resistant materials permit uses in most environments, including offshore oil platforms.