21
mvip@mitech-ndt.com
(and depending on the warn sound settings an acoustic one).
Note: The measurement series is automatically completed when the currently set number of
measurements per series (average times) is reached. The following measurement is then the first
value of the new measurement series.
5.3 Conversion Deviations
Measurements with a set conversion produce a scattering. The conversion deviation is the variance
resulting from the comparison of measuring values observed with different hardness testing methods. It
includes 2 components. The major share is caused by the fact that there is no clear physical relationship
between the various methods. The second component results from the circumstance that the
comparison of the hardness values (e.g. HL value and Brinell) also includes the measuring deviation of
the method being compared to. Therefore, a conversion between hardness values contains inaccuracies
from the outset.
This applies not only to conversion of the HL value into static indentation hardness values, but also for
converting from one static hardness measuring method to another. The conversion deviations (±HB, ±HV,
etc.) represent “standard deviations”, i.e. 68% of all materials tested to date fell within the specified
variance range.
Comparing hardness values with each other is thus always subject to inaccuracies. This not only holds
true for the conversion of the HL value to static hardness values but also for the conversion of one static
hardness value to another.
If the measurement series is not yet closed, a conversion scale can be selected at any time: before,
during or after the measuring process.
Number of impacts per measuring area
Test each measuring area by at least 3 to 5 impacts.
Do not impact the same point more than once.
If the range within the same measuring area exceeds R
≧
30HL, check whether the surface of the
sample has been adequately ground or whether the sample yields or flexes during the test impact.
Minimum spaces between impact points
Impact device types
Distance of center of the two
indentations
Distance of center of the
indentation to sample edge
mm
mm
D
、
DC
3
5
DL
3
5
D+15
3
5
G
4
8
E
3
5
C
2
4
