SENSORS GUIDANCE
Types of sensors
Pellistors are normally recommended where fast recovery time and restriction to flammable gases is required. Under adverse conditions loss of sensitivity, called poisoning can occur.
Electro-chemical cells provide specific gas detection at threshold limit value levels for most toxic gases. Their major advantage is low power consumption enabling personal and portable monitors to be practical but, since they are essentially small electric cell generators, they have a limited lifetime even when not exposed to the gas they are detecting, typically 2 to 4 years is obtainable. Recent advances have enabled detection at temperatures between -5º C and +50º C.
Semi-conductor sensors have made major advances in recent years and now provide a highly reliable, comparatively low cost solution to many applications. They are robust, do not poison and do not have the limited lifetimes, which affect other types.
Infra-red gas sensors use an infra-red light source and a filter to select the target gas wavelength. The presence of gas alters the amount of light getting to the sensor which provides the detection output. IR sensors are reliable, very quick to respond, are immune to contamination, virtually maintenance free,
Categories of use
Safe Area description to follow.
Intrinsically safe (I.S) description to follow.
Flameproof description to follow.