The Honeywell 705 Combustible Gas Sensor is an explosion proof assembly, fitted with poison-resistant combustible gas detection elements. Fully encapsulated, it is designed for use in hazardous locations. The Sensor is electro-catalytic and consists of 2 beads of refractory oxide, formed on a fine platinum wire coil. The active bead is coated with a catalyst material, while the reference bead is glass coated.
In the presence of gas, the catalyst coated bead promotes the oxidation of the gas, causing it to heat up and increase in electrical resistance. This change of resistance, relative to the reference bead, can be measured and is in direct proportion to the concentration of combustible gas.
