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gas detection tech info

Catalytic Gas Detectors Contaminants

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Tech Info

Catalytic type combustible gas sensors are relatively generally low-cost devices and have been in use for a very long time. Depending on the installation properties and characteristic, they may offer reliable gas detection but, in some installations, and subject to the surrounding environment, they can cause operators various problems and ultimately may reduce safety.

 Catalytic type detectors do not have self-check. They can fail shortly after calibration and operators will not know until the next round of checks which may be months away. End users would like to at least get an installed service life of 2 to 3 years per catalytic gas detector, however depending upon the installation conditions this can be much shorter.  There are many factors that can lead to signal loss and/or premature failure of catalytic gas sensors, including:

  • Clogging of the flame arrestor chamber by airborne dirt and oil
  • Water submersion or direct impingement into the sensing chamber
  • Continuous exposure to background combustible gases
  • Inadequate or excessive sensor power
  • Prolonged exposure to low oxygen/anaerobic environments
  • Loss of sensitivity (poisoning) due to exposure to some external substances

Various manufacturers now offer poison resistant catalytic detectors and recommend regular maintenance to extend the service life and accuracy of their catalytic detectors, however the technology has its limitations that cannot be avoided in various installations.

All catalytic combustible gas sensors are affected by “poisoning”, which is the result to exposure to various compounds available in some surrounding environment. A catalytic detector can be damaged (or poisoned) when vapours irreversibly tie up the adsorption sites on the active element, erode the element’s catalytic coating, or cover the element with an impervious coating.

The level of damage that a catalytic detector sustains when exposed to contaminants is related to various factors:

  • the type of contaminant,
  • the concentration level, and
  • the length of time.

Some of the contaminants that are known to poison a catalytic gas detector include:

  • Silicone oils, greases, and resins (RTV silicone sealant)
  • Halogens (chlorine, bromine, fluorine, iodine, halon, freon)
  • Tetra- and trichloroethylene
  • Dichlorobenzene
  • Vinylchloride monomer and PVC vapors
  • Hydrochloric acid
  • Phosphate esters
  • Silanes
  • Phosphorus
  • Gasoline antiknock compounds, i.e. tetraethyl lead and tetramethyl lead

Generally, manufacturers offer a 12 months warranty on catalytic detectors, however this warranty does not cover damage to the sensor caused by exposure to known contaminants.

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