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ECOPROBE 5 - rs dynamics

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13. IR ANALYZER<br />

IR ANALYZER<br />

• Infrared radiation is essentially heat radiation. This fact will be familiar to anyone who has ever felt the<br />

heat radiated from a hot oven, and has observed the dark red glow arising when the heat becomes<br />

stronger.<br />

• Most gases have their characteristic spectrum in the infrared range. Those spectra reflects a molecule’s<br />

composition in such a way that no two molecular gases have the same IR spectrum. IR spectra are the<br />

fingerprints of gases, and thus allow gases to be uniquely identified.<br />

• By transmitting a beam of IR radiation through air, or through any particular volume of gas, and<br />

recording how much is transmitted at selected spectral lines, one may determine which gases are<br />

present and their respective concentration.<br />

Infra-red Detection<br />

IR source<br />

Gas input<br />

69<br />

Three selective optical filte<strong>rs</strong> plus<br />

one for a reference channel.<br />

Gas output<br />

IR<br />

Four detecto<strong>rs</strong> for TP,<br />

CO2, Methane and a<br />

reference channel.<br />

A beam of IR wide spectrum radiation passes through the sampled gas column which moves through the IR<br />

tube (Fig. 25). This causes oscillation of the sub-microscopic particles of the compound. Oscillation consumes<br />

energy at a group of particular spectral lines creating a phenomena known as infra-red atomic absorption. The<br />

consumed energy is directly proportional to the concentration of the measured compound. Therefore the higher<br />

the concentration, the higher the absorption of energy at the characteristic wavelength. Each selective optical<br />

filter lets through only one wavelength of the radiation typical for the measured compound. A detector behind<br />

the optical filter measures the attenuation of the energy that is directly proportional to the measured<br />

concentration.<br />

Field experience has proved that an IR analyzer is essential for a general Soil Contamination Survey because<br />

the contaminant concentration is often above 4000 ppm, ppm,<br />

where PID detection cannot be used.<br />

If hydrocarbons are present in the contaminant, consequent continuity continuity<br />

between PID and IR outputs can be<br />

observed.<br />

Applications of <strong>ECOPROBE</strong> 5 IR Analyzer<br />

Fig. 25 – Schematic presentation of an IR analyzer.<br />

1. Relative and fast in situ monitoring of contaminant vapor with a concentration up to<br />

500 000 ppm.<br />

2. Separate reading for methane, hydrocarbon group and CO2.

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