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.
Advantages
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.
Disadvantages
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.
