Replacing obsolete RF frequency generator

Thread Starter

treaddeskuser

Joined Nov 29, 2020
5
I have a 90's vintage (ultrasonic, rf?) cleaner with a transducer in a large vat and an RF Amp that drives the transducer (300W or so). The RF amp says it uses a pulsed input and is driven by the board in the image. I'd like to replace this with a stand-alone frequency generator so it can be run manually leaving the rest of the system untouched. Ideally I'd like the ability for a new computer (or PLC) to turn the signal on or off but don't need control of the power from the computer. In it's youth I suspect the system was run at different power levels but is now always run at full power.

I don't know the voltage or signal from this board. I may be able to find someone who is around the system to 'scope it but that hasn't happened yet.

This is out of my domain of expertise and I'm not quite sure where to start. What pitfalls/challenges should I be watching for? In particular, I really need to not damage the RF Amp, it is the same vintage as the card and so not easily replaced.

Thanks in advance for any pointers, education, advice you can offer. Please let me know if this should be in a different thread.
freqcard.jpg
 

Thread Starter

treaddeskuser

Joined Nov 29, 2020
5
A little more information. The output seems to be just less than 1MHz 1V so an XR2206-based solution may work. If I just go with a low-cost XR2206 board would you foresee a problem if I just switched the whole board - the 12V supply - on/off? I'm concerned that might leave me with some floating outputs which may not be ideal. (I'm a little concerned about the longevity of the XR2206 board, but they are inexpensive enough to replace).
 

Alec_t

Joined Sep 17, 2013
14,220
The RF amp says it uses a pulsed input and is driven by the board in the image.
That board is very likely designed to drive the transducer at its resonant frequency (not the same thing as the pulse frequency), which would vary somewhat with the acoustic load.
I'd like to replace this with a stand-alone frequency generator so it can be run manually
How will you recognise what the needed resonant frequency is, in order to set the f-gen manually?
 

Thread Starter

treaddeskuser

Joined Nov 29, 2020
5
Thanks for the response. I'm open for suggestions on how to determine all the information I need. The short video I have of the oscilloscope screen seems to show a constant sine wave. I'm told 800kHz, 1v That was at the maximum power of the amp so would it make sense that this is a 100% duty cycle for the pulse (but it seems unlikely that the generator and amp were matched that precisely)?1698848520323.png
 

Thread Starter

treaddeskuser

Joined Nov 29, 2020
5
One thing that may be my misunderstanding, is I describe the next component as an amp, but it seems smarter than that. There is some sort of match network further down the line. Does that help with the transducer resonant frequency question or is that still something that has to be considered at the frequency generator stage?
 

Alec_t

Joined Sep 17, 2013
14,220
The blurry scope shot in post #4 doesn't give much away, does it? Where in the circuit does the waveform appear? What are the X and Y time/voltage scales?
There is some sort of match network further down the line. Does that help with the transducer resonant frequency question
Who knows? We can't see what you've got in front of you.
I'm told 800kHz, 1v That was at the maximum power of the amp
I can't believe that an ultrasonic transducer in a cleaner operates from only 1V.
Can you post a pic of your set-up, plus any make/model data?
 
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