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5 Sensor Principle
5.1 Operating Principle for DraegerSensor PR
and LC
The DrägerSensor is a transducer for measuring the partial pressure of
combustible gases and vapors contained in ambient air. It uses the heat-of-
combustion principle.
The monitored air diffuses through the sintered metal disc into the sensor.
There the mixture of combustible gases and vapors are catalytically combusted
at a heated detector element (pellistor). The monitored air supplies the Oxygen
required for the combustion. Due to the resulting heat-of-combustion, the
detector element gets hotter. This increase in heat causes a change of
resistance in the detector element, which is proportional to the concentration
of the mixture of combustible gases and vapors in the monitored air.
In addition to the catalytically active detector element, there is an inactive
compensator element. Both elements are parts of a Wheatstone bridge.
Thus environmental effects like changes in temperature or humidity are
almost entirely compensated.
5.2 Contaminating Gases for DraegerSensor PR
and LC
Vaporous silicon- and lead-compounds, sulfurous compounds such as
hydrogen sulfide and sulfur dioxide, phosphorous compounds such as
phosphine. Acidic vapors such as hydrogen fluoride, hydrogen chloride,
hydrogen bromide and halogenated organic compounds such as refrigerants
and tri- or tetrachloroethene.
A calibration check might be necessary, if the sensor was exposed to a high
concentration of combustible gases or vapors for an extended period of time
or to contaminants as listed above.
Sensor Principle
Operating Principle for DraegerSensor PR and LC
Contaminating Gases for DraegerSensor PR and LC
Principle of operation
1 Sintered metal
2 Detector bead
3 Sensor housing
4 Compensator bead
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