This is an end-of-the-day job, except for the wettest or most demanding
applications.
Captured water vapour forms a layer of ice on the condenser. The thickness
of this layer grows at the rate of ~26microns for every milligram (mg)
of captured water vapour. To put this into context, with a typical
volar forearm TEWL of 10g/(sq.m h), it would take over 2.5 hours of
continuous measurement to accumulate 1mg of ice.
The main effect from ice build-up is a gradual change of calibration,
attributable mainly to the reduction of measurement chamber length.
This is illustrated by the measurements below, where ice was accumulated
by repeatedly calibrating an AF200 instrument by the droplet method
with 1mg droplets.
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