Hello Franc,
These info are useful and they explain to me much about ultrasonics.
Now, all explained!!! I can understand that transducer/tank/water can
affect the resonant frequency. That's why the noise is different when the
tank is full or half empty; some times it works much away from the resonate
frequency because it makes louder noise (I feel it). It seems, it works in a
steady frequency.
I understand that needs the schematic someone to know how to increase the
frequency. In the first I thought it would be easy someone to recognize the
design. Seeing that the final transformer has only 3 pins, and the fact that
the mains supply direct the transducer (as you said amplitude modulated) I
understand the design should be more complicated. After all that, I closed
the ultrasonic leaving it working the usual way!
"Franc Zabkar" wrote in message
...
On Sun, 17 Aug 2008 22:26:53 +0300, "Yianni" put
finger to keyboard and composed:
The other ultrasonic with the conventional buzzer (20mm diametre, less
than
1mm thick) claims 30W!!!
Now, I understand the difference with a "real" ultrasonic with two "real"
transducers I have had. Time comparison for the same cleaning results:
a. Real ultrasonic 60W : 0.5 min
b. the ultrasonic we talk (50W) : 9 min
c. the other ultrasonic with the buzzer (30W) : 25 min...
Look at it another way. Why would you need a 7 amp relay to supply
power to a "buzzer"? Why would you need such a large heatsink and two
high current (?) transistors?
I suggest you buy something like this ...
http://www.p3international.com/produ.../P4400-CE.html
... and measure the power consumption for yourself.
It makes no sense to say that a transducer can "resonate" at twice its
resonant frequency (unless you are talking about overtones maybe ???).
Yes, I thouhgt the second overtone.
I'm guessing that the cleaner's circuit automatically oscillates at
the transducer's resonant frequency, ie the external components aren't
that critical. I suspect that if you were to replace the transducer
with a higher frequency type, the new transducer would oscillate at
its own resonant frequency, not 42kHz. You may need to optimise some
components, though, to ensure that the transducer looks like a pure
resistance. The frequency characteristics of the ferrite toroid would
need to be considered as well.
I don't know to say if it's correct or not. I'm just thinking.
1.. The transducer (ceramic ultrasonic transduder, like a bigger buzzer)
it
has a mass of say 25g. It is glued on the tank, say 100g. And the tank is
filled with water 400-600g. I wonder for its resonance frequency.
2.. Just a question because I don't know. Could someone take a
conventional
small buzzer and make a circuit to work on the buzzer's resonace
frequency,
relying on the buzzer's characteristics without RC or other similar parts
on
the oscilator? If yes, then it is a possibility to be the same in this
machine.
I had another look at the following patent. It suggests that a simple
change to your circuit may enable your transducer to resonate at the
first overtone (see Fig 3 of the PDF file). It also confirms that the
resonant frequency is dependent on the mass of water.
OSCILLATOR CIRCUIT FOR AN ULTRASONIC CLEANER
http://www.freepatentsonline.com/3584244.html
The author states that "since the piezoelectric disc is closely
coupled to the tank and the water load, the water depth in the tank
effects the power transferred to the water and the resonant frequency
of the transducer".
"On all ultrasonic cleaning systems, some means must be employed to
control the frequency at which the generator drives the transducer. If
the generator is made to operate at a fixed frequency, poor
performance will be encountered, since it is generally not possible to
select one frequency which will always provide optimum operating
conditions."
"In the case of an ultrasonic generator, one is concerned with the
behaviour of a piezoelectric transducer at the fundamental and perhaps
the lower order overtone frequencies."
This part looks very interesting:
================================================== ==================
The preference the circuit shows in operating in the vicinity of some
initially selected frequency is also desirable in suppressing
tendencies to run at overtone frequencies. In some circumstances,
however, this effect might not be great enough to completely prevent
operation at the overtone. For instance, if the series resonant
impedance of the fundamental frequency is slightly greater than at the
first overtone, the circuit preference for lower impedance could take
precedence and result in operation at the overtone were the shunt
capacitor 86 not employed.
Since the capacitor 86 is connected across the feedback transformer
primary, its capacitive reactance lowers the impedance to overtone
frequencies. This results in a lower primary voltage or, more
directly, an increase in core saturation time. Thus, any tendencies to
run an overtone are adequately suppressed, forcing the circuit to run
at the fundamental.
In the example given, it is desirable to operate at the fundamental
frequency. Nevertheless, if operation at an overtone is desired, this
may be accomplished by suitable selection of circuit elements and
constants, and the principles of the invention may be employed to
enhance operation at the preferred overtone.
================================================== ==================
- Franc Zabkar
--
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