Check spectrometer samples
In contrast to recalibration samples, check spectrometers samples have composition corresponding to those of qualities to be analysed or have such low alloy concentration that they lie on the calibration curves produced with calibration samples.
Again in contrast to recalibration samples,
check samples have analysis values which have been determined, using different
procedures, in at least 5 laboratories producing such qualities. Their analyses
are reliable within narrow limits.
The high expenditure incurred for CRM is not
necessary for check samples. In the case of CRM the main is not to bring as
many as elements as possible into a few samples collected to form a set. When
using such samples for high-speed steel only “auxiliary calibration curves”
should be plotted, these being supplemented by means of calibration samples
corresponding to the high speed steel qualities.
Check samples can be used in various ways
on spectrometers. After the spectrometer has been calibrated, the check samples
are analysed a number of times in the recalibrated state. The spectrochemically
determined values must agree with the given value within ±2SR of the
calibration curve and both values must be reported. If there is no agreement,
calibration or recalibration is insufficient. Correct calibration of the
spectrometer can be tested by the user by means of the check samples:
a) If the user does not have confidence in
the spectrometric analysis of an unknown sample,
b) at regular intervals in order to
increase quality assurance
c) to check the need for recalibration. In
this case the sample can be used for type recalibration.
Method is recommended particularly if
relatively few samples per day are measured with the spectrometer and these
samples belong to only a few quality groups.
The individual elements in the check
samples must be assigned sensible limits based on the spectrochemically
determined value. If , at the time of time of the check procedure, all the
values determined are within these ± tolerance nothing
need be done. If they are outside, recalibration is necessary.
The actual recalibration values determined
with recalibration samples and the actual check values determined with check
samples should be recorded and assessed by statistical methods. This leads to
increased operational reliability of the spectrometer and provides information
on actual stability and the frequency of recalibration. The last-mentioned also
leads to saving in material for calibration samples.
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