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Slide 36
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Catalytic Sensors
  • Theory - Combustible gas is oxidized on catalytic element. The change in temperature causes a change is resistance that is measured by the meter.
  • Gases Measured - combustible
  • Advantages - long life




Combustible sensors contain two coils of fine wire coated with a ceramic material to form beads. The "active" bead is coated with a palladium based material that allows catalyzed combustion to occur on the surface of the bead. The "reference" bead lacks the catalyst coating, but in other respects exactly resembles the active bead. Any combustible vapors which are present will be subject to catalytic combustion on the surface of the active bead, heating this bead to a higher temperature. The temperature of the untreated reference bead is unaffected by the presence of gas. The difference between the temperatures of the two beads is proportional to the amount of combustible gas present. Since the beads are strung on the opposite arms of a Wheatstone Bridge electrical circuit, the instrument perceives this as a change in the electrical resistance in the circuit. It is this change in resistance due to differential heating that is used by the instrument to provide a reading.

Biosystems Web Site
http://www.biosystems.com/appnotes/equiv3.htm

 
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