FISCHER FISCHERSCOPE X-RAY XDLM 231, Operator'S Manual

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Trueness of measurement readings Measurement device monitoring for the Fischerscope X-RAY
FISCHERSCOPE
®
X-RAY 111
Variations The variations of an X-ray fluorescence instrument depend on the
measurement parameters measurement time, distance between
the detector and the specimen, intensity of the primary beam and
other characteristics of the instrument as well as on the physics of
the X-ray fluorescence with regard to the measurement application.
It is interesting that with the X-ray fluorescence method, the
variations of the readings can be calculated theoretically from the
spectrum of a single reading such that a measure for the variation
can be specified with one single reading. The standard deviation is
used to evaluate the
repeatability precision of the instrument with
regard to the measurement application, the feature to be measured
and the setting parameters of the instrument. The better the
repeatability precision of the instrument, the less the measurement
results will be ”falsified” by the instrument. Thus, a good
repeatability precision is considered an important quality feature of
an instrument and is of particular importance when evaluating the
suitability of a measurement device .
Guaranteed Error
The calibration standards are subject to a ”measurement
uncertainty” as well because their nominal values are obtained
through measuring. For this reason, the nominal values of the
standards also include an error, the
guaranteed error (e.g., 5% of
the nominal value) that includes the mean value, and its interval
should include the true value.
15.4 Trueness of measurement readings
The repeatability precision of an instrument must not be confused
with the
trueness of a reading. The trueness of a measurement
result is determined by comparing the mean value B of a test series
of a sample, for example a calibration standard or a reference
sample, with its known value A that has been
recognized as being
correct , the nominal value. The trueness is represented by the
difference B – A between the mean value and the nominal value.
The measurement result is correct if the difference B – A is near
Zero.