Today there are a variety of sensors used to detect flammable gases. There are also many different flammable conditions, each requiring a specific type of sensor to be accurately measured. When selecting a gas monitor for detecting flammable gas, it is critical that you understand the differences and choose the appropriate sensor for the environment to be measured.

Catalytic Bead

Traditionally catalytic bead type sensors have been used in instruments designed for detection of flammable gases and vapors. The catalytic bead is a very fine wire that is coated with a catalyst material, typically platinum or palladium. This bead is then heated to a temperature sufficient to promote combustion of a flammable gas or vapor on the surface of the catalyst. This combustion generates heat, which in turn changes the resistance of the wire inside the bead. The resistance change is monitored by an electrical circuit (typically a Wheatstone bridge) and used to generate an electrical signal proportional to the concentration of the gas or vapor. The electrical signal is received by a microprocessor, which then generates a digital reading onto a display. For over 50 years the catalytic sensor has proven to be a very reliable way of determining whether the atmosphere in enclosed or confined spaces contains an unsafe level of gas that could, with the addition of an ignition source, result in a fire or explosion. However a potential disadvantage of the catalytic bead sensor is that it requires oxygen to operate. Because the catalytic bead sensor must combust the gas to produce a reading, oxygen is required when this sensor is used.

LEL and UEL Ranges

Reprinted with Permission from Bruce Holcom - RKI Instruments, Inc