APMP.M.H-S3 Final Report Comparison on Hardness ... - BIPM

Revision: <strong>Final</strong> <strong>Report</strong>
Date: May 25, 2012
10. Discussion and Conclusion
From the above comparison results, the CMC claimed by the participated NMIs in
the HRA scale is reaffirmed and hence they are acceptable. Also, it can be seen
from the figure 8 that the variation of hardness measurement by different NMI at the
prescribed nominal values is less than 0.25HRA. This indicated that a CMC value of
0.30 HRA is possible to achieve by NMIs for hardness primary standard.
Deviation (HRA)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Figure 8 Variation of hardness measurement in Rockwell scale A
Similarly, the variation of hardness values measured by different NMI at the given
nominal values for the HRB scale is shown in figure 9. Here, unlike in the case of
HRA scale, the deviation shown in the hardness measurement is very large
(0.50HRB) for the lower range of HRB values i.e. for the soft materials having
nominal values less than 60HRB. However the deviation reduces to 0.20 HRB in the
higher range of HRB scale, ie for the relatively harder materials having the nominal
hardness value more than one. This observation strongly suggests that NMI can
achieve still a lower CMC in the higher range of hardness values (>60 HRB) for
hardness primary standard
Deviation (HRB)
30 40 50 60 70 80 90 HRA
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
Deviation Possible CMC achievement
20 30 40 50 60 70 80 90 100HRB
Deviation Possible CMC achievement
Figure 9 Variation of hardness measurement in Rockwell scale B
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