26. February 2024 © Copyright 2024, PROCEQ SA 12
3 Measurement Principle
The measuring principle of the ultrasonic method is based on the evaluation of changes that
an ultrasonic wave undergoes in a component due to scattering or reflecting from internal
objects.
The ultrasonic wave is generated on the component surface, in this instrument by piezoelectric
excitation, and propagates as an elastic wave in the component.
When propagating through the material, the wave interacts with the material structure
whenever it encounters a boundary to a material with a different acoustic impedance and is
scattered along it. For example, in the case of concrete, this occurs at the layer boundaries of
the aggregate to the concrete matrix.
On parts of the inner structure, for example, reinforcing bars or cladding pipes, parts of the
switched-on energy are backscattered and reach the surface again. A large proportion of the
energy is reflected on the backwall of a component (e.g. at a concrete/air boundary).
To create and record the sound energy, transducer elements of various types are used as
transmitters and receivers, which are connected to ultrasound devices for measurement and
presentation of results. Transmitters and receivers are arranged differently depending on the
method used.
Depending on the accessibility of the component, the transmitter and receiver are placed on
the same side of the component, which is referred to as a reflection arrangement. Procedures
that are used using this method are referred to as pulse-echo procedures. If access from both
sides is possible, this is referred to as a transmission arrangement or through-sound
transmission.
The speed of sound can be determined very easily using transmission. This can be
experimentally related to material parameters such as concrete compressive strength or the
solidification process of fresh concrete.
If amplitudes recorded in a pulse-echo arrangement are plotted over time, the depth of objects
and the thickness of the component can be determined if the speed of sound is known.
PD8050 uses ultrasound pulse echo technology, in which both the transducers and receivers
are placed on the same side of the component. This is used to detect objects with a different
acoustic impedance, such as air voids (cracks, delaminations), rebars, honeycombs, etc.
The Pundit has 3 rows of 8 transducers for a total of 24 transducers. A channel is a group of
transducers operating together.
The Pundit has 8 channels: the 3 transducers in the same column are connected in parallel.
One channel transmits and the echoes are received by the other seven channels. Each
channel transmits in turn.
In transmission, the transducers in the same channel will pulse simultaneously.
In reception, the signals recorded by the transducers in the same channel will be summed
together.
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