6 Calibration of the flux meter
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6.2
The influence of pumping flow
We have carried out some sets of measures utilizing the same injected flux but
with different pumping flow from the accumulation chamber to the detector.
The pumping flow was changed by means of a mechanical flow reducer and
measured with an Alicat Mass flow meter.
We have not noted a significant variation of the measures except when the
pumping flow is less than 200 SCCM.
The diagram shows the plot of the measurement error versus the imposed flux
of carbon dioxide (expressed in grams per square meter per day) at different
pumping flow rates.
In order to avoid unwanted variation of pumping flow due to power supply the
pump is supplied at 12 V DC with a stabilized voltage regulator.
The pumping flow, after the power supply stabilization, is 1000 SCCM ± 20%.
The efficiency of pump can vary due to dust or moisture in the pump body.
Periodic maintenance is necessary.
The mixing device was suspected, by some researcher, to affect the accuracy of
the flux measurement. In our experience the precision of the measurements
was noteably reduced without a mixing device present. In the two plots below
the measurements at various regimes of mixing device rotation are reported.
