Empirical Calibrations - GE Moisture Image 1 Series Service Manual

June 2003

Empirical Calibrations

A-28
For those liquids in which a Henry's Law type analysis is not
applicable, the absolute moisture content is best determined by
empirical calibration. A Henry's Law type analysis is generally not
applicable for the following classes of liquids:
•
liquids with a high saturation value (2% by weight of water or
greater)
•
liquids, such as dioxane, that are completely miscible with water
•
liquids, such as isopropyl alcohol, that are conductive
For such liquids, measurements of the hygrometer dew point readings
for solutions of various known water concentrations must be
performed. Such a calibration can be conducted in either of two ways:
•
perform a Karl Fischer analysis on several unknown test samples
of different water content
•
prepare a series of known test samples via the addition of water to
a quantity of dry liquid
In the latter case, it is important to be sure that the solutions have
reached equilibrium before proceeding with the dew point
measurements.
Note: Karl Fisher analysis is a method for measuring trace
quantities of water by titrating the test sample against a
special Karl Fischer reagent until a color change from yellow
to brown (or a change in potential) indicates that the end
point has been reached.
Either of the empirical calibration techniques described above can be
conducted using an apparatus equivalent to that shown in Figure A-3
on page A-33. The apparatus pictured can be used for both the Karl
Fischer titrations of unknown test samples and the preparation of test
samples with known moisture content. Procedures for both of these
techniques are presented below.
Application of the Hygrometer (900-901D1)