Thickness Measurements - Leica DM R Serie Mode D'emploi

Microscop ic measurement and comp arison in
metallograp hy
Linear measurements with measurement grati-
cules
The size of the line patterns and the length of the
divisions are designed for the standard
magnifications customary in metallography. For
standard magnifications one graticule division
has the following rounded values in the object
plane:
standard magnification:
100x – 1 division approx. 10 µm
standard magnification:
200x – 1 division approx. 15 µm
standard magnification:
500x – 1 division approx. 12 µm
standard magnification:
1000x – 1 division approx. 11 µm
The exact proportions of measurement divisions
in the microscope can be checked by using
stage micrometers, calibration standards or
microscales.
Graticules for grain and p article size determination
The graticules for the standard series and
Snyder Graff methods contain a test circle
which the viewer sees as having a diameter of
80 mm at standard magnification. Its size
therefore conforms with the standard picture
series charts, facilitating size comparison.
These graticules also include a measured length
to allow the Snyder Graff line sectioning
method. This and similar methods involve
counting the number of grains cut by the
measured distance. An average grain size can
be worked out by taking several measurements.
108
1
The graticule for ASTM-E 112 grain size
measurements is divided into eight segments
with numbered grain sizes. The pictures
conform with grain size plate no. 1 of the ASTM-
E 112 standard. We refer to the ISO/DIS 643,
Euronorm 103/71, DIN 50 601 and ASTM-E 112
standard specifications for taking grain size
measurements with the named graticules.
Digital length and height measurement using TV
technology: see separate Leica MFK 2 manual.

Thickness measurements

In principle, thickness measurements can be
carried out if both the upper and the lower
surface of the object can be clearly focused.
The difference in
(mechanical dual knob focusing: distance
between two divisions = 2 µm) gives a value for
transmitted light objects that is falsified by the
refractive index of the object (which has been
"transfocused") and perhaps immersion oil. The
true thickness of the object detail measured in
transmitted light is given by the vertical stage
movement (focusing difference) d' and the
refractive indices n
medium between the coverglass and the
objective
d = d'
n
o
d = d'–––
n
i
d = d'
stage height
of the object and n
o
setting
of the
i