FISCHER FISCHERSCOPE X-RAY XDLM 231, Operator'S Manual, Page: 118 / 236

Measurement device monitoring for the Fischerscope X-RAY Practical monitoring of the measurement devices
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X-RAY
reading differences. It is not without reason that the X-ray
fluorescence method is considered the most accurate
measurement method for coating thicknesses due to its high
comparative precision. Because the most common and grave
deviations are of a systematic nature, they must be found and
corrected. This is the task of measurement device monitoring.
15.7 Practical monitoring of the measurement
devices
How to test?
A measurement application that is calibrated and checked using
calibration standards and if necessary corrected and documented,
is considered
secure . Measurements with a secure measurement
application provide correct measurement readings. This condition
should essentially continue for a long period, however, as
mentioned above, the measurement application can change,
because inevitably sooner or later the instrument changes. Users
must, therefore, check and if necessary correct each measurement
application regularly and as often as is economically feasible.
NOTE:
For the Fischerscope XRAY with the WinFTM Soft-
ware, each product file contains in addition to the
measurement application for the sample a parallel
measurement application for the calibration stan-
dards (with an identical calibration but with a poten-
tially different substrate material). The parallel
measurement application can be used to measure
the calibration standards. Thus, the problem men-
tioned does not exist: a substrate material correction
when re-measuring is unnecessary and the test is,
therefore, simpler.
We recommend performing the checks using reference samples or
calibration standards. They are well suited for long-term monitoring
because one can assume that the samples do not change over a
long period as opposed to the measurement application and thus
one can easily recognize changes of the measurement application.
A reference sample is a coated storage sample from the production
that corresponds in its structure (order and composition of the
coatings and substrate material) to the measurement application to
be checked, and that exhibits a marked measurement spot
(
reference area ) and that is positively identifiable. Within the
reference area, the reference sample should exhibit essentially no
coating thickness differences, referenced to the mean value.
Checks with reference samples offer the advantage that the
reference samples are less expensive, that they can always be
replaced by new samples, that the standards are spared and that
the check may therefore be carried out more easily. Reference