Catalytic Gas Detectors Principle

Catalytic gas detectors are based upon the principle that when gas oxidizes it produces heat, and the sensor converts the temperature change via a standard Wheatstone Bridge-type circuit to a sensor signal that is proportional to the gas concentration. The sensor components consist of a pair of heating coils (reference and active).

The active element is embedded in a catalyst. The reaction takes place on the surface of the catalyst, with combustible gases reacting exothermically with oxygen in the air to raise its temperature. This results in a change of resistance.


There is also a reference element providing an inert reference  signal by remaining non-responsive to gas, thereby acting as a stable baseline  signal to compensate for environmental changes which would otherwise affect the sensor s temperature.


The major advantages of catalytic detectors:

  • Robust.
  • Simple to operate.
  • Easy to install, calibrate and use.
  • Long life with a low replacement cost.
  • Proven technology with exceptional reliability and predictability.
  • Easily calibrated individually to gases such as hydrogen which cannot be detected using infrared absorption.
  • Can perform more reliably in dusty & dirty atmospheres as they are not as sensitive as optics to the build up of industrial contaminants.
  • Can perform more reliably in high temperature applications.
  • Are less sensitive to humidity and condensation.
  • Not as significantly affected by changes in pressure.
  • Can detect most combustible hydrocarbons.


The limiting factors in catalytic detector technology:

  • Catalysts can become poisoned or inactive due to contamination (chlorinated & silicone compounds, prolonged exposure to H2S and other sulfur &/or corrosive compounds).
  • The only means of identifying detector sensitivity loss is by checking with the appropriate gas on a routine basis and recalibrating as required.
  • Requires oxygen for detection.
  • Prolonged exposure to high concentrations of combustible gas may degrade sensor performance.
  • If flooded with a very high gas concentration, may show erroneously low or no response, and sensor may be damaged or rendered inoperable.
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