Jeulin 223 008 Mode D'emploi page 37

Ultrasounds
Moduson table
Ref :
223 008
3 Operation
3.1 Ultrasonic reflection and absorption
These experiments are proposed as a complement to the various experiments that can be
performed with the MODUSON system.
The main transmitter is used in the Continuous position. It must be set beforehand at
resonance via the Frequency knob so that a signal with the highest possible amplitude is
transmitted. The BNC connector of the transmitter is connected to the MODUSON
transmitter 2 placed inside the circular recess on the moulded table. This transmitter sends
an ultrasonic wave towards a metallic mirror located at the middle of the recess.
The MODUSON receiver is also placed inside the circular recess. It senses the reflected
signal. The maximum amplitude of the received signal is found by observation on the screen
of the oscilloscope to which the receiver is connected.
The setup demonstrates or verifies the equality of the angle of incidence and of the angle of
reflection.
If the mirror is turned over, the reflective surface is replaced by plastic foam. Then the
incident signal is entirely absorbed.
Note: The reflection of ultrasonic waves on the mirror goes along with a diffraction of the
reflected signal. Owing to the small width of the mirror (4 cm), this phenomenon in not
inconvenient: the centre peak is sharp enough and the secondary peaks are sufficiently
weak and away from the main peak so that measurements can be easily performed in fifth
forms.
3.2 Ultrasonic interference phenomena
The main transmitter (P/N 222 027 or 222 076) is assumed to be set at its maximum
transmission level. It is connected to the MODUSON transmitter 2.
• The two transmitters connected to the same signal generator are synchronous sources.
phase selector
Note: Depending on the main transmitter and transmitter 2 used, the signal received at
switch
point 0 by the receiver when the two transmitters have identical amplitude settings may
happen to yield a zero minimum instead of a peak. Then the two transmitters vibrate in
opposition of phase instead of vibrating in phase as would be expected. To put them in
phase, activate the phase selector switch.
ENGLISH
However, the following adjustments are required to give them an identical amplitude:
1. Install the two transmitters in the magnetic recess on the moulded PVC table. Place
them at a distance of e.g. 2 cm from each other (smallest distance). Place a receiver
in one of the arc-shaped recesses opposite the zero-degree angle value (then the
receiver is located on the median of the segment joining the two receivers and it is
equidistant between them) and connect it to the vertical input of an oscilloscope.
2. Disconnect the transmitter 2 and observe the signal transmitted by the main
transmitter and sensed by the receiver. Record the amplitude value. Connect the
transmitter 2 and switch the main transmitter OFF (in this position, the transmitter
member is off but the generator is not and continues delivering the same signal on the
BNC connector, hence to the transmitter 2), then only the transmitter 2 is active. Using
the transmitter potentiometer, trim the amplitude of the received signal so that the
amplitude value is identical to the previous reading.
3. Switch the main transmitter ON: then the two transmitters operate simultaneously and
they have the same amplitude. This produces a peak that is sensed by the receiver (a
slight position adjustment by 1–2 degrees may be necessary to obtain this peak).
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