Combustible Gas Detector Principle

Fire & Gas System
1

Combustible Gas Detector (Catalytic Sensor Type)

A detector that senses the presence of combustible gas.

Principle of Operation:

The principle of operation of the catalytic sensor shall depend upon the oxidation of flammable gas, which causes the temperature of catalytic sensing element (filament, pellistors, bead) to change as a function of the concentration of gas detected.

A bridge circuit shall be used to determine the changes in electrical resistance and the apparatus shall be calibrated to provide indications of gas concentrations.

Selection Criteria for Combustible Gas Detector (Catalytic Sensor Type):

Following are some minimum requirement applicable for combustible gas detector selection, however requirements vary from industry to industry.

• The apparatus shall be suitable for the detection of combustible gases or vapour concentrations with air from 0% to 100% LEL.

• The αetector shall be a self contained device comprising of sensor element and any monitoring and signal conditioning electronics required to provide a linear 4-20 mA output signal to monitoring cards in the main fire and gas panel.

• The gas detector housing shall be supplied complete with sensor unit,terminal housing, flashback arrestor, collecting cone and any other attachments necessary to enable the detector to function correctly in the ambient conditions.

• The time of response of the detector t50 shall not be greater than 10 secs, and t90 shall not be greater than 30 secs.

• Normal variations in the ambient conditions shall not aftect the performance of the detectors.

• The apparatus shall be so designed and constructed that it is not capable of itself igniting a combustible gas air mixture.

• Detectors shall be provided with poison resistant sensors, which shall protect against poisoning caused by organic and silicone based vapour poisons.

• Provision shall be made for testing the 삐etectors by application of test gas. The method employed shall not necessitate the removal of dust and splash filters, gas collecting cones or similar attachments.

• The alarm output contacts or signal outputs of a combustible gas detector shall be of a latching type requiring a deliberate manual action to reset.

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