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Calibration
The most accurate results can be obtained if the instrument is calibrated
for the material under test.
• This is done by performing a pulse velocity measurement on a section
of the structure of known thickness.
• Alternatively, perform the automatic estimation of pulse velocity as de-
scribed in chapter 3.4.
Physical influences on the Measurement
Inhomogeneities (e. g. aggregate particles, voids) in concrete influence
the propagation of an ultrasound pulse. They will scatter the signal. The
effect is very large if the size of the aggregate is equal to or larger than the
wavelength of the ultrasonic signal. This influence is significantly reduced
when the wavelength is at least twice as large as the aggregate size. It
also follows that it is very difficult to detect an anomaly if it is smaller than
half the wavelength.
The Pulse Echo Transducer is a shear wave transducer with a frequency
of 50 kHz.
Assuming a typical pulse velocity of 2500 m/s, the wavelength is 50 mm.
This means that anomalies smaller than 25 mm will be invisible.
Effect of sample size
The geometry of the object is very important for obtaining good results.
• The maximum penetration depth depends on the quality of the con-
crete and also on the amount of rebars present. Typically the maximum
transmission depth lies between 50 cm (19.7”) and 1m (39.4”).
• Generally, the minimum lateral dimension should be two times the
thickness of the object, or the depth of the anomaly you are trying to
detect. The reason for this is that if the object is too narrow, reflections
from the side walls will interfere with the echo from the rear wall.
4. Explorer
From the main menu select Explorer to review saved files.
Tap on a saved file to open it.
Return to the Explorer list by pressing the back button. To delete a file tap
in the check box to the left of the file and delete it.
Tap on the add folder icon to create a new folder to keep measurements
organized.
To save measurements in a particular folder, select the folder, then exit
explorer using the hardware button.
Subsequent measurements will be stored in this folder.
Exit a folder and return to the higher directory by pressing on
.
