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

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Trueness and precision Measurement device monitoring for the Fischerscope X-RAY
FISCHERSCOPE
®
X-RAY 115
This can be observed, for example, with round robin tests on the
same sample with a marked reference area, even if each
instrument is correctly calibrated and checked. The reasons are the
random deviations of each single reading, and thus of each mean
value of a test series, the random deviations at each calibration,
and also the fact that each calibration standard is labeled with a
nominal value that through its measurement is also afflicted with an
unavoidable deviation from the true value (expressed by the
uncertainty of the standard). The sum of these deviations is
expressed in the
comparative precision of the measurement
method. The repeatability precision characterizes the random
deviations of the results that are obtained at
one instrument by one
person with one and the same sample at the same measurement
location at repeated measurements, i.e., under repeatability
conditions. Comparative precision describes the random deviations
between different instruments, calibrated with different calibration
standards, at repeated measurements performed by different
persons at the same sample using the same measurement
locations (measurements under comparable conditions).
Theoretically, there should be trust between the supplier and
customer. However, the reality is: ”Trusting is good, inspecting is
better!”. One of the most important prerequisites for the inspections
is correct measurement readings. However, different readings
between supplier and customer should generally not be taken as a
cause to continuously doubt the measurement results or
measurement methods of the other party or to demand arbitration
measurements with different methods that are to verify that one’s
own measurement is correct. First one should investigate whether
the measurement results have been obtained at the same
measurement spots and the same specimens. To answer this
question, supplier and customer should exchange and measure the
same samples with marked measurement spots. If the results are
still different, the involved instruments should be calibrated using
certified calibration standards. This determines which instrument
measures correctly and which instrument requires corrective
measures. If the differences remain and the problem cannot be
resolved, only a well-founded consultation through experts of the
instrument manufacturer may help in the end.
Each user who monitors the measurement devices as described
herein, can verify the trueness of his own measurements at any
time. He can also trust his measurement results and will not be
troubled by unwarranted complaints. In practical situations, the
systematic deviations, which almost always arise from inadequate
or infrequent monitoring of the measurement devices, occur more
significantly and more frequently and above all are of a greater
magnitude than the random deviations between the instruments of
different parties. Typically, the random deviations are hardly
noticed and if they are noticed, they are accepted due to their
insignificance. Thus, random deviations as opposed to systematic
ones can usually be neglected as the reason for measurement