West Systems Portable diffuse flux meter, Руководство пользователя

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6 Calibration of the flux meter
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Calibration of the flux meter
The present chapter reports the procedure followed by WEST Systems to check
the fluxmeter calibration. The method described refers to carbon dioxide
calibration, bu the same procedure is followed for the other gases.
CO2 fluxes from soil are simulated by injecting a known flow of gas into the
accumulation chamber. The interface between the accumulation chamber and
the calibration table is built to minimize the gas leakage.
The apparatus is schematized in figure.
The injected flux is controlled and measured with a precision mass flow
controller. This MFC, calibrated for CO2, is electronically stabilized, with
accuracy: ± (0.8% of R 0.2% of Full Scale).
6.1 Fluxmeter calibration
For fluxes between 300 and 700 moles/m 2 /day, the injected flux is controlled
by means of a mechanical flow reducer and measured using a bubble flowmeter
(Accuracy 3%) before and after the flux measurement with the accumulation
chamber.
Two series of measure were performed for flux of 300 moles/m 2 /day to evaluate
the coherence between the two different methods of flow measurement.
A thermometer and barometer were utilized to measure the barometric pressure
and the air temperature during the experiment in order to select the correct
accumulation chamber conversion factor.
A flow meter is utilized to measure the pumping flow during the experiment.
During all the measures a 100% CO2 flow was utilized. The same procudure
was utilized to check the instrumental response to methane and hydrogen
sulfide.
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Mass flow controller
100% carbon dioxide (or target gas)
cylinder and pressure reducing valve