Two-Point Calibration; Blasted Surfaces - Trotec BB 20 Manual De Instrucciones

Two-point calibration

Make sure that the measuring instrument is in single
measurement mode . Two films of different thicknesses
are required for this measuring method . If possible, the
thicker film should be approx . one and a half times thi-
cker than the thinner film . In order to obtain the best
possible results, the assumed layer thickness should
lie between the two calibration values . This method
is particularly well suited for measurements on rough
shotblasted surfaces and for very precise measure-
ments . It is advisable to carry out an average value
measurement several times . This reduces the effect
of scattering, which can occur during the calibration of
upper and lower values . The calibration films can be
used in any order:
1. Perform a zero-point calibration as described in the
previous section .
2. Perform a single-point calibration with film 1 as de-
scribed in the previous section .
3 . Repeat step 2 with film 2 .
4 . Perform the measurement by holding the probe
against the coating to be measured and remove the
probe again after the beep sounds . The measured
value appears on the display .
1. Place the probe against the sample several
times.
2. The film should be approximately as thick as
the estimated layer thickness of the object to
be measured.
3. The film calibration can be performed as often
as necessary during an ongoing series of mea-
surements. The old calibration is over-written;
the zero calibration remains in the memory
until it is carried out again at a later date.
4. Further details can be found in the section on
single-point calibrations.
Shot-blasted surfaces
Due to the physical nature of (shot-)blasted surfaces,
the layer thickness measurements are usually too
high . The average thickness over the peaks can be
determined as follows .
B - 8
Operating manual – layer thickness measuring instrument BB 20
Method A
1. Perform the steps for the single and two-point cali-
bration as described above . Use a smooth sample
with the same surface curvature and the same
substrate as the object to be measured subse-
quently .
2. Perform approx. 10 measurements on the uncoated
(shot-)blasted sample in order to determine the
average value "Xo".
3. Then perform approx. 10 measurements on the
coated (shot-)blasted sample in order to determine
the average value "Xm".
4 . The difference between the two average values
yields the average layer thickness "Xeff". The larger
standard deviation "s" of the two values Xm and Xo
should also be taken into account: Xeff = (Xm - Xo) ±s
Method B
1. Perform a zero-point calibration with 10 measure-
ments on the blasted, uncoated sample . After that,
perform a film calibration on the uncoated substrate .
The calibration should be performed with a number
of different films with a maximum thickness of 50
microns, which, in the appropriate combination,
are approximately as thick as the assumed layer
thickness .
2 . The layer thickness can be read directly from the
display and should be averaged on the basis of 5 to
10 individual measurements.
Method C
Proceed initially as described in the two-point cali-
bration with two films (see section 4 .2 .3 .) In order
to simulate the surface characteristics as closely as
possible, the film value can be achieved by the use of
several 50 µm thick films . The average coating thick-
ness should be determined on the basis of 5 to 10
individual measurements . The statistics function has
proven to be very useful here .
A rough surface is considered to be insignificant
where the layer thickness exceeds 300 µm . the
calibration methods mentioned above need not be
applied in this case .
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