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INFRARED POINT GAS DETECTION
Principle of operation
Infra-red (IR) gas detection is based on the absorption of energy by hydrocarbons. The
bond between hydrogen and carbon absorbs proton energy at a wavelength of 3.3m m.
A beam of IR energy is emitted between a source and detector and any attenuation caused
by hydrocarbons in the short beam being electronically processed to give a reading in LEL
(Lower Explosive Limit). Commonly a reference beam is utilised to overcome any reduction
in beam intensity due to fouling of the optics, fog, temperature effects etc.
Advantages
- Unit is ideal for areas where gas is likely to collect, it is more commonly being used
in conjunction with line of sight gas detectors..
- Very fast response, however the use of sinters can effect this.
- Limited maintenance required.
- Minimal drift.
- Limited covert (hidden) failure potential, hence being used in 1oo1 (one out of one)
configurations. This however has some drawbacks- see disadvantages below.
Disadvantages
- Only measures at a particular point.
- Greater sensitivity to heavier hydrocarbons, for instance if you are measuring methane
and there is a condensate release it is likely that high LEL readings will result.
Therefore it is essential that the possible gas compositions are carefully considered
before opting for a 1001 configuration. ( In this combination under these circumstances
false trips may result).
- Cannot measure non hydrocarbons eg., hydrogen.
- Gassing the detector with test gas can be a problem with some detectors, however most
manufacturers have test cells. it must be noted that test cells require a higher
concentration of test gas as it is only introduced across a small part of the optical
path. The use of test wands with a clear plastic sheet being introduced is likely to
become a feature because of consistent results.