Working of Catalytic bead sensor in Gas Detection.

Catalytic bead sensor

• Under certain circumstances flammable gases and vapors can be oxidized by the means of air ‘s oxygen to release the heat of reaction.This is achieved through special and suitable heated catalyst material which slightly increases its temperature by heat of the reaction .this increase in temperature is the measure of gas concentration.

• So called pellistors are very tiny porous ceramic beads embedding a small platinum wire coil. There is an electric current flowing through the platinum wire so that pellistor is heated to some hundred degree Celsius.

  

  Pellistor

• If the ceramic bead contains some suitable catalytic material the pellistors temperature will rise in presence of flammable gas and the platinum wire coils resistance will increase accordingly. This change in resistance wrt resistance change in clean air is used for electronic evaluation.

•  One pellistor is alone not suitable for detection of flammable gases and vapours. It needs a second one to compensate for environmental parameter and it needs to be explosion protected. By means of flameproof enclosure and sinter disk  a useful catalytic bead sensor results.

• The compensator pellistor is built  very similar to active pellistor but does not contain the pellistor material so that gas cannot be oxidized. If the ambient temperature changes resistance of both pellistor changes and there is  no bridge signal.

• However if gas is present only the resistance of active pellistor changes and the wheatstone bridge is balanced.