H68.0.03.6C-02 Operating Manual GMI 15 plus page 10 of 12
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10.2 CM-Moisture
The CM-moisture (unit [CM%]) is often used for materials like floor screed. This moisture rating is
correlated to the moisture u: it is calculated by the same equations. It is measured by the CM-
method (destructive testing with high complexity). It is the only accredited measuring method
(besides the time-consuming oven-dry method) for floor screed measurements in Germany.
The values measured with CM-method
and oven-dry method (%u) may differ for
some materials. Especially for building
materials containing cement CM-
measurements will always get lower
values than oven-dry measurements.
The conversion is material-dependent,
because the differences between both
values depend on the used product.
The conversion shown in the left picture
is a practicable approximation.
For gypsum, gypsum plaster and anhydrite screed the value %u equals approximately the CM-
value.
11 Adjustment
The accuracy can be checked with the testing probe PW 25 (optional accessories).
Select the material “rEF” and run the zeroing function (p.r.t. chapter 6.5).
Lay the device onto the testing cube. If the device displays a different value than the value printed
on the cube for the GMI 15, you can use the slope correction to adjust the device:
Displayed value rEF =(measured value rEF * (1 + slope correction / 100 )
Follow these instructions to adjust the device:
Switch the device off.
Press and keep it pressed, while turning the device on (press shortly).
Release the hold-button not before the first parameter “S. 25” is displayed.
Set parameter with up or down .
Jump to the next parameter by pressing .
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