Waygate Technologies Krautkramer USM 100, Руководство по эксплуатации, Страница: 168 / 330

5 Operation Calibration
168 Rev. 9 (09/2023) Krautkrämer USM 100
Calibration using dual-element probes
Dual-element probes are especially used for wall thick-
ness measurements. The following special features
should be taken into account when using these probes:
V-path error
Dual-element probes produce a V-shaped sound path
from the pulser via the reflection from the backwall to the
receiver element. This V-path error affects the measur-
ing accuracy. You should therefore choose two wall
thicknesses that cover the expected thickness mea-
surement range for the calibration. In this way, the V-
path error can be corrected to a large extent.
Higher material velocity
Due to the V-path error, a higher material velocity than
that of the material to be tested is given during calibra-
tion, especially with small thicknesses. This is typical of
dual-element probes and serves for the compensation
of the V-path error.
With thin wall thicknesses, the effect described above
leads to an echo amplitude drop which has to be espe-
cially taken into account with thicknesses <2 mm.
A stepped reference block having different wall thick-
nesses is required for calibration. The wall thicknesses
must be selected in such a way that they cover the ex-
pected measurement readings.
Note
Always keep in mind that the measurement
value is determined at the intersection point
of the gate and the echo flank if the function
Gate A TOF Mode has been set to Flank .
The correct setting of the echo height and the
gate threshold is therefore decisive for the
accuracy of calibration and measurement!
Calibrations or measurements in Peak mode
require some experience when using dual-
element probes in order to choose and set
the correct echoes.