4 Measuring flux
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The chamber was removed from the soil.
The duration of the flux curve recording is
normally in the interval 90-240 seconds. Only
when measuring very low flux of hydrogen
sulphide
or
VOC
a
300-480
second
measurement could be necessary.
The following images show a series of common accumulation shapes.
The “perfect” curve
The shape of the curve is quite perfect and the
computation of the flux is done with a very good
accuracy: R
2
(regression quality factor) very close
to 1.
Air contamination
The flux curve is no longer linear; the linear best fit
curve do not fit exactly the flux curve as pointed out
by the regression quality factor (0.815 in the
example). This effect is probably due to
atmospheric air contamination.
If you obtain this kind of curve check the sealing of
the accumulation chamber with the soil or check
that tubes, filters and pump are intact.
