Don Foreman -- ultrasonic transducer

Don, I have the same transducer as you do, the 40 kHz Langevin transducer:
http://www.steminc.com/piezo/langevin_40.asp
Now that I am done with the trailer, etc, I can start looking into making an ultrasonic cleaner from this transducer. I would like to hear if you have any suggestions for a simple oscillator that would make this transducer work properly. I would prefer simple to design over cheap.
Also, what kind of stainless tank would you suggest for it.
thanks
i
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On Wed, 28 Feb 2007 13:22:54 -0600, Ignoramus4664

There are some schematics on Branson's website. See, e.g., http://www.bransonic.com/drawings/913-242-095.pdf
I have a hunch (but don't know for a fact) that L1 and/or T2 in the referenced schematic may be square-loop inductors. I have some small squareloop toroids if you want a couple. You'd need to strip them and wind them with what is needed. The MOSFET's cited are obsolete, no problem. Pick any 400-volt several-amp TO-220 MOSFET, there are many good choices at Digi-Key for a buck or two, or I could send you a coupla those as well.
I don't have any ideas for SS tanks other than see what you can scrounge as surplus medical or thin kitchenware. I don't think there's anything critical other than thin is good. Ya might find a good thin SS tank in a discarded deep fryer.
I found the "magic epoxy" at a local distributor -- for 50 bux a tube. I've somehow managed to contain my enthusiasm for grabbing a tube. A single 70W 'ducer probably won't have a lot more moxie than the $49 HF unit. Larger cleaners use several 'ducers.
I haven't played with my xdcr yet other than just fooling at the elex bench. May not get around to that for a while. Truth be told, the HF unit is working fine for me. I wanted the 'ducer for other experiments, as perhaps coupling ultrasound directly into a liquid-filled fouled firearm barrel with some sort of matching horn.
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wrote:

Don, how big of a tank can I use with this transducer. (not sure how big is your HF tank)
Also, I have a fundamental question. What if I simply build a variable frequency, variable power oscillator circuit with a big amplifier. I could even attach an amplifier to a wavetek that I have. Then I could carefully select proper resonant frequency that matches this transducer.
Which I think is easy with some ICs, a little trim pot and a darlington of one sort or another.
Would that not be enough to make this transducer make ultrasound noise?
What am I missing here? I looked at that schematic. Did not really understand what it does, specifically why there is a second transformer with two primaries.
thanks
i
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On Thu, 01 Mar 2007 09:01:57 -0600, Ignoramus23363

Don, I found something interesting that explains why there is a second transformer.
http://www.repairfaq.org/REPAIR/F_samschem.html#SAMSCHEM_041
Chapter 14) Ultrasonic cleaner schematic
Ultrasonic cleaning is a means of removing dirt and surface contamination from intricate and/or delicate parts using powerful high frequency sound waves in a liquid (water/detergent/solvent) bath.
An ultrasonic cleaner contains a power oscillator driving a large piezoelectric transducer under the cleaning tank. Depending on capacity, these can be quite massive.
A typical circuit is shown below. This is from a Branson Model 41-4000 which is typical of a small consumer grade unit.
R1 D1 H o------/\/\-------|>|----------+ 1, 1/2 W EDA456 | C1 D2 | +----||----+----|>|-----+ | .1 uF | EDA456 | 2 | 200 V | +-----+---+ T1 +---+------->>------+ | R2 | _|_ C2 )|| o 4 | | | +---/\/\---+ --- .8 uF D )|| +----+ | | | 22K _|_ 200 V )||( + | | 1 W - 1 o )||( )|| _|_ +-----------------+---------+ ||( O )|| L1 _x_ PT1 | R3 | 7 ||( )|| | | +---/\/\---+ +-----+ ||( 5 + | C \| | 10K, 1 W | F )|| +---+ | | Q1 |--+-+--------------+ 6 o )|| | | | E /| | D3 R4 +---+ +----+------->>------+ | +--|<|---/\/\--+ _|_ | 47, 1 W | --- Input: 115 VAC, 50/60 Hz | | | Output: 460 VAC, pulsed 80 KHz N o------+-------------------+---+
The power transistor (Q1) and its associated components form an self excited driver for the piezo-transducer (PT1). I do not have specs on Q1 but based on the circuit, it probably has a Vceo rating of at least 500 V and power rating of at least 50 W.
Two windings on the transformer (T1, which is wound on a toroidal ferrite core) provide drive (D) and feedback (F) respectively. L1 along with the inherent capacitance of PT1 tunes the output circuit for maximum amplitude.
The output of this (and similar units) are bursts of high frequency (10s to 100s of KHz) acoustic waves at a 60 Hz repetition rate. The characteristic sound these ultrasonic cleaners make during operation is due to the effects of the bursts occuring at 60 Hz since you cannot actually hear the ultrasonic frequencies they use.
The frequency of the ultrasound is approximately 80 KHz for this unit with a maximum amplitude of about 460 VAC RMS (1,300 V p-p) for a 115 VAC input.
WARNING: Do not run the device with an empty tank since it expects to have a proper load. Do not touch the bottom of the tank and avoid putting your paws into the cleaning solution while the power is on. I don't know what, if any, long term effects there may be but it isn't worth taking chances. The effects definitely feel strange.
Where the device doesn't oscillate (it appears as dead as a door-nail), first check for obvious failures such as bad connections and cracked, scorched, or obliterated parts.
To get inside probably requires removing the bottom cover (after pulling the plug and disposing of the cleaning solution!).
CAUTION: Confirm that all large capacitors are discharged before touching anything inside!
The semiconductors (Q1, D1, D2, D3) can be tested for shorts with a multimeter (see the document: "Basic Testing of Semiconductor Devices".
The transformer (T1) or inductor (L1) could have internal short circuits preventing proper operation and/or blowing other parts due to excessive load but this isn't kind of failure likely as you might think. However, where all the other parts test good but the cleaning action appears weak without any overheating, a L1 could be defective (open or other bad connections) detuning the output circuit.
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On Thu, 01 Mar 2007 09:13:43 -0600, Ignoramus23363

There ya go! Steminc has confirmed that these transducers can take up to 2KV if properly matched to the load. They suggested using a bit more liquid than "normal".
If/when I get motivated to work with my 'ducer I'll post my wanderings and flagellations. At the moment, however, this project is not on my priority list. It does appear to be on yours, so lead on!
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Ignoramus23363 wrote:

...
That is an impressive ASCII drawing! That took either a helluva lot of patience, or an ASCII CAD app. I wonder if there are any ASCII drawing app's? Bob
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On Thu, 01 Mar 2007 09:01:57 -0600, Ignoramus23363

The HF tank is about 6-5/8 x 5-3/8 x 2-5/8 deep.

That'd work, but tuning would be fussy. The Q of these xdcrs is about 1000, so the 3dB bandwidth is about 40 Hz at around 40 KHz. It might be tricky to adjust a Wavetek to that degree of precision and stability. My Wavetek wanders about 20 Hz when set as close to 40,000.0 Hz as I can get it.

Possibly, if your oscillator is stable enough and at the right freq.

If you refer to TX2, that's a gate drive current xfmr with two secondaries, driving the MOSFET half-bridge. Circulating current in the resonant load will "pull" the oscillator into some semblence of synchronism.
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wrote:

I see. That makes sense.

Well, I suppose that there are plenty of stable oscillator chips out there.

Thanks Don. I am beginning to understand better.
What size tank, you think, would be the biggest tank that could work with a 70W transducer?
i
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On Thu, 01 Mar 2007 12:46:24 -0600, Ignoramus23363

I don't know. There may be some minimum power density for cavitation, but I don't know how much ultrasound disperses laterally in a liquid. It probably is related to the ducer lateral dimensions in wavelengths. Some fishing and depthfinder sonars (higher freq) have fairly narrow cones.
Tank size may not make much difference if the ultrasound tends to be mostly in a cone above the 'ducer -- though little or no cleaning would occur in regions away from the cone. Larger cleaners have multiple transducers.
Cleaners seem to have a recommended range of depths. That may have something to do with standing waves in the vertical column of liquid.
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wrote:

I will try to use this bucket:
http://igor.chudov.com/tmp/stainless-bucket-on-wheels.jpg
it is 12" diameter on top.
i
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@NOSPAM.23363.invalid says...

As a point of comparison, the Branson tsnks that I'm familiar with in this size range use 12 xducers and 500W power supplies.
Ned Simmons
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I don't think that this will work, even if one is willing to ride the controls, because the resonant frequency of the transducer will vary with temperature, which will be rising because of the high power being applied. Temp will eventually more or less stabilize, but it will never be constant enough. This is why such transducer drivers use the transducer itself to set the frequency.
Joe Gwinn
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