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Ultrasounds
®
Moduson
2 transmitter telemeter 12V
Ref : 222 082
The entire device is shown below:
2.3 The measurements
As soon as one of the receivers is moved (for example the receiver A to the right), the
corresponding signal also moves to the right of the time axis (provided that the
synchronisation channel is properly selected). The receiver A which was moved, receives
the emitted signal with a delay t which depends on the distance d separating the receiver B,
as shown in the diagram opposite.
The measurement of time t on the oscilloscope screen and distance d on the graduated ruler
on the rails gives a direct measurement of the velocity of sound in air: V = d/t.
Measurement of the duration t is better if we select an angle of the burst signal waveform
(such as the point M of the figure above) and if we increase the gain of the signal
corresponding to the receiver A that moves away from the transmitter to compensate for the
attenuation of the signal because of the distance. We can also increase the horizontal sweep
speed and select a lower adjustment duration (0.5 ms/div).
2.4 The results
For a single measurement, if a time t = 1 ms is read (that is one division on the screen with a
selected measuring range), the distance is d = 34 cm, which leads to a velocity of V = 340
m.s -1.
It is also possible to measure some values of the time t (by using the markings on the time
axis of the oscilloscope) and obtain values of corresponding distances d:
This helps conclude that the velocity of ultrasound waves is constant.
ENGLISH
B
Transmitter
t: time (in ms)
d: distance (in cm)
Velocity (in m/s)
A
d
0.2
0.4
0.6
0.8
7
14
20.5
27.5
350
350
341
343
15
1
34
340
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