Combustible Gas alarm
Combustible gas alarm usually provide readouts in % of LEL (Lower Explosive Limit), in the 0 to 100% range. The lowest concentration, in air, of ignitable vapours corresponds to 100% of the LEL. Therefore, a combustible gas which has a LEL of 100% at 4% volume in air would produce a readout of 50% of the LEL if only 2% of the volume of air is that gas.
The most popular sensor is the catalytic combustion sensor which consists of a Wheatsone bridge circuit containing a heated platinum filament. More recent models, called catalytic treated beads use a coiled platinum wire embedded in a porous ceramic bead. With both types of sensor, the gas, oxidized by the filament, creates a change in the electrical resistance which is proportional to the combustible gas concentration. The sensor res-ponds to any gas or vapour which burns in the presence of oxygen. However, a non-linear response is obtained with high concentrations of combustible gas or when incomplete oxidation occurs due to insufficient oxygen supply.
The sensor can also burn out in high concentrations of combustible gases and will not operate properly with oxygen concentrations below 16%. Coverage of the surface of the catalyst's active sites by decomposition of poisoning compounds such as silicon, lead, phosphorus and halogen compounds can hinder the activity of the sensor. Operating life of the sensor is 24-36 months.
The concentration given by the instrument is true only if the gas being detected is the same as the gas used for the calibration of the instrument. Therefore, an instrument calibrated with pentane can only approximate the pre-sence or absence of other combustible gases. The alarm settings usually take this into account by being set at 10 to 20% of the LEL.
Our company has the kind of product---KAB gas alarm
KAB gas alarm adopts catalytic gas sensor with advanced technology and superior craft. It provides visual and audible signals when the gas concentration, such as LPG, natural gas, coal gas etc, reaches the preset level. It reminds you to take prompt favorable action. You may start up other link equipment, like opening windows or shutting off gas supply, to avoid fire, explosion, suffocation, and other malignant accidents.