Zeiss METROTOM 1500 G3, Operating Instructions Manual, Page: 83 / 120

Setting up the workpiece and measurement
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– The higher the voltage, the higher the energy of the photons in
the X-ray spectrum. This leads to an improved radiolucency of
the objects.
– Low-energy photons are already absorbed in the spectrum by a
filter. The resulting spectrum is therefore harder.
Beam hardening
Beam hardening is the shifting of the X-ray spectrum towards a higher
average photon energy. It results from an irregular attenuation of the X-
ray radiation: low-energy X-ray radiation is more strongly absorbed by
the workpiece than high-energy radiation. Beam hardening causes un-
desired artifacts and should therefore be minimized.
Principle:
– A workpiece with low attenuation of the X-ray radiation causes little
beam hardening.
– Filters are used to reduce beam hardening.
The thicker a filter, the better the effect. However, in absolute terms,
a thicker filter also absorbs a larger portion of the radiation. This can
be offset by selecting longer integration times and sufficiently high
image averaging. Therefore, long measuring times are required due
to the use of very strong filters.
Defining and selecting the filter in the software
For the following operations, please refer to the METROTOM OS Operat-
ing Instructions.
Before you carry out a new measurement, you will have to select the in-
serted filter in the Inspector for CT measurement. The »Prefilter« pull-
down window is provided for this purpose
Some filters are predefined. You can also define your own filters. To do
so, open the Inspector for the X-ray tube. You can create customized fil-
ters under »Filter«
NOTE
Scattered radiation correction can only be performed correctly for pre-
defined filters. In addition, a parameter file is required for scattered radi-
ation correction.
Automatic filter changer (option)
If your CT system is equipped with a filter changer, you can insert your
own filters into the filter changer and define them in the software. See
the operating instructions for the user software.