Principle Of Operation - Elcometer SCM400 Operating Instructions Manual

2 PRINCIPLE OF OPERATION

Soluble salts on the surface are taken into solution by placing a wetted 110 mm
diameter Elcometer 130 SCM400 High Purity Sample Paper on the area to be
sampled.
By leaving the paper in contact for a timed period, salt removal from the surface
is maximised. Using a paper of known size allows contamination to be
expressed in terms of surface area.
These papers retain a known amount of water because of their consistent
absorbency characteristics and therefore the concentration of the solution
formed is related to the quantity of soluble salts removed.
The sample paper containing the salt solution is placed over the electrodes on
the Elcometer 130 SCM400 and its resistivity is determined. This is achieved by
measuring the minimum resistance of the solution over a fixed solution path
length and cross section, governed by the electrode spacing and paper
thickness respectively.
The solution concentration is inversely proportional to its resistivity. The
Elcometer 130 SCM400 relates the latter to a calibration with known
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