Campbell EC155, Руководство по эксплуатации продукта

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EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
57
Where:
• P = irradiance after passing through the optical path
•
Po = initial irradiance
•
ε
= molar absorptivity
• c = analyte concentration, and
•
l = path length.
In the EC155, radiation is generated by applying constant power to a tungsten
lamp, which acts as a 2200 K broadband radiation source. Specific
wavelengths are then selected using interference filters located on a spinning
chopper wheel. For CO
2
, radiation with a wavelength of 4.3 µm is selected, as
it corresponds to the molecule’s asymmetric stretching vibrational band. For
H
2
O, radiation at 2.7 µm, corresponding to water’s symmetric stretching
vibrational band, is used.
The EC155 is a dual wavelength single beam analyzer; thus, rather than using a
separate reference cell and detector, the initial intensity of the radiation is
calculated by measuring the intensity of nearby, non-absorbing wavelengths
(4 µm for CO
2
and 2.3 µm for H
2
O). These measurements account for any
source and detector aging and window contamination.
The chopper wheel spins at a rate of 60 revolutions per second, and the
detector is measured 512 times per revolution. The detector is maintained at –
40 °C using a three-stage thermoelectric cooler and is coupled to a low noise
pre-amp module.
The EC100 electronics digitize and process the detector data (along with
ancillary data such as sample-cell temperature and pressure) to give the CO
2
and H
2
O concentration for each chopper wheel revolution (60 Hz), filtered to
the user-specified bandwidth. The EC100 also synchronously measures and
processes data from an optional CSAT3A 3D sonic anemometer head.