23
6
Press
key when CAL is selected
to carry out the calibration. The valid calibration
is briefly confirmed and carried out.
7
Save the calibration result to current
channel file.
5.2 Calibration with Dual-Element (TR) Probes
Dual-element (TR) probes are especially used for wall thickness measurement. The following
peculiarities must be taken into account when using these probes:
Echo Flank
. Most dual-element (TR) probes have a roof angle (transducer elements with inclined
orientation toward the test surface). This causes mode conversions both at beam index (sound entry into
the material) and at the reflection from the backwall, which can result in very jagged echoes.
V-Path Error
.Dual-element (TR) probes produce a v-shaped sound path from the pulse via the
reflection from the backwall to the receiver element. This so-called “V-path error” affects the measuring
accuracy. You should therefore choose two wall thicknesses that cover the expected thickness
measurement range for the calibration. In this way, the V-path error can be corrected to the greatest
possible extend.
Higher Material Velocity
Due to the V-path error, a higher material velocity than that of the test material
is given during calibration, especially with small thicknesses. This is typical of dual-element (TR) probes
and serves for compensation of V-path error.
With small wall thicknesses, the above-described effect leads to an echo amplitude drop which has to be
especially taken into account with thicknesses less than 2 mm.
A stepped reference block having different wall thicknesses is required for calibration. The wall
thicknesses must be selected so that they cover the expected readings.
Calibration Process
We recommend to use the semiautomatic calibration function for the calibration with T/R probes.
1
Set the required test RANGE
2
Increase the probe delay until the two calibration echoes selected are displayed within the
range
3
Set the pulse and receiver functions according to the probe used and the test application.
4
Select the function group PDELAY.
5
Enter the distances of the two calibration echoes in S-REF1 and S-REF2.
6
Position one gate on the first calibration echo.
7
Position the other gate on the second calibration echo.
8
Press
key when CAL is selected to trigger the calibration.
The correct calibration is confirmed by the message “Calibration is finished”. The instrument will now
automatically determine the sound velocity and the probe delay and set the corresponding functions
accordingly. The value of the function P-DELAY will be set to the correct value.
If necessary, check the calibration on one or several known calibration lines, e.g. using the stepped
reference block.
5.3 Distance Amplitude Curve
The instrument is available with Distance Amplitude Curve (DAC) function. Functions for the
distance-amplitude curve are accessed through the DAC Menu, which is located by pressing
DAC
AVG
.
