A catalytic bead sensor is a type of sensor that is used for

combustible A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

gas detection from the family of gas sensors known as pellistors.

Principle

The catalytic bead sensor consists of two coils of fine platinum wire each embedded in a bead of alumina, connected electrically in a

Wheatstone bridge A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of the circuit is its ability to provid ...

circuit. One of the pellistors is impregnated with a special catalyst which promotes oxidation whilst the other is treated to inhibit oxidation. Current is passed through the coils so that they reach a temperature at which oxidation of a gas readily occurs at the catalysed bead (500-550 °C). Passing combustible gas raises the temperature further which increases the resistance of the platinum coil in the catalysed bead, leading to an imbalance of the bridge. This output change is linear, for most gases, up to and beyond 100% LEL, response time is a few seconds to detect alarm levels (around 20% LEL),Catalytic bead sensor
/ref> at least 12%

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

by volume is needed for the oxidation.

Issues

Catalyst poisoning Catalyst poisoning refers to the partial or total deactivation of a catalyst by a chemical compound. Poisoning refers specifically to chemical deactivation, rather than other mechanisms of catalyst degradation such as thermal decomposition or physic ...

- because of the direct contact of the gas with the catalytic surface it may be deactivated in some circumstances. *

Sensor drift A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

- Decreased sensitivity may occur depending on operating and ambient conditions. *Modes of failure - which include poisoning and sinter blockage, they become apparent during routine maintenance checking.

References

{{reflist Gas sensors

Principle

Issues

See also

References