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How can I test ultrasonic transducers

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julio_w

New Member
Hi All,

I am trying to build a large ultrasonic cleaning bath, I already bought 50 PZT transducers 60 Watts and 40 Khz each from a supplier on china, and I am going to buy a 3 Kw ultrasonic generator to connect all transducers in parallel.

So before buying the large generator I wanted to test the transducers one by one just to be sure that what i get is what i order, so I decided to buy from ebay one small ultrasonic cleaner of 50 Watts 40 Khz and then I was thinking in replacing the transducer with the new ones one by one and test.

So my question is how do I test? I know you can do the foil test but that will just tell me that there is ultrasound going on but I want to know the actual frequency of the transducer. So can I just buy a transducer receiver that cost around 2$ and connect at the terminals an oscilloscope? not even sure if that is possible.

Thanks for reading and I would appreciate your help.
 

kubeek

Well-Known Member
Most Helpful Member
Yes that probably would work. For a simple works - doesn´t work test an ear is enough, I can hear the ultrasonic baths at work very well and it is a very annoying sound.
 

julio_w

New Member
I guess what you hear is the vibration generated by the transducers somehow but that will let me know that it is working but not at what frequency, I have read that a receiver only will not tell me the frequency either so I am back to square 1 (no idea how to do it) and as well seems that i wasted 40$ on the small ultrasonic cleaner that i bought as it is very likely it will be another kind of transducer that may need different voltage to generate the ultrasound...

Any ideas on how can i archive this?
 

languer

Active Member
A nice sensitive microphone is one method.

You could also measure the voltage across its terminals (with oscilloscope) as you sweep its input. To do this properly you should monitor both voltage and current, but if I recall correctly such transducers behave like parallel tanks; which means the voltage should be at a maxima at (or near resonance). To drive it properly you must do this through a low impedance (e.g. output of OPAMP).
 

julio_w

New Member
I found this schematic for a bat detector, they claim they can detect up to 100 khz and basically divide the frequency by 16 to get an audible signal...

BatDetSch.gif

So I was thinking that if that is true I could do something similar eliminating the frequency divider, so it will looks like:

BatDetSch2.GIF

So if I attach an oscilloscope at the exit of IC2 i should be able to measure the frequency, am i right?
 

languer

Active Member
You can, and perhaps I misunderstood you. I thought you had a batch of (plain) transducers which you wanted to verify what their resonant frequency was. To use (plain) transducers you must drive them; meaning you must have a drive which generates the desired frequency (or frequencies). If you have a transducer with a built-in driver; which you want to measure the frequency, then you can do as you suggest; or you can just connect the driver output to an oscilloscope and look at the waveform.

If you do not know the frequency response of these transducers then the method I provided will give you a close-enough idea. Another idea (based on what your last example) is to use two of your transducers; one for transmit and one for receive. Drive the transmitter with a low-impedance source (OPAMP) sweeping frequencies, the receiver you connect to an oscilloscope (through an OPAMP preferably - for isolation, though not a must). You watch the oscilloscope signal as you sweep the transmitter frequency. The signal will peak around the frequency both transducers peak at (plot signal output magnitude vs input signal frequency).
 
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