Ultrasonic Meassurement 1

[Erick D]

Hello

I got some ultrasonic baths cleaners that we use on the semiconductor industry to clean parts. Our tanks are not uniform as far as intensity goes. I am trying to measure the signal from the generator to the ultrasonic transducer with an oscilloscope. The connection type of the transducer to the generator it looks like a BNC type. I bought a Y (tee) BNC adapter (50 ohm) to measure the power being transmitted to the transducer from the scope. I wanted to see if the 7 transducers I have (each with its own gen) were creating constructive/destructive interference with each other. I am getting very high spots and very low spots in the ultra sonic tank. When I hook up the scope to the BNC Y adapter it seems to cause a short. My scope prove its rated for the voltage so I am not understanding what I am doing wrong. The goal is to have a uniform intensity across the ultrasonic tank.

Any tips?

Thank you very much.

 

[IRstuff]

Is your scope on 50-ohm termination? Any unpowered transducer likely has high impedance, like piezo. You might even need a signal conditioner.

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[VEBill]

"...7 transducers... ...creating constructive/destructive interference... ...very high spots and very low spots in the ultra sonic tank."

With reflections from hard (reflective) walls, all that is entirely predictable.

Microwave ovens have a similar problem with hot spots, and they use turntables or 'stirring' to mitigate.

---

"....When I hook up the scope to the BNC Y adapter it seems to cause a short."

Low impedance cable and/or parallel capacitance. Don't do that.

You might want to use a scope probe (Hi-Z) directly at the sample port side of your BNC 'T', instead of a coaxial cable.

A scope probe on a BNC 'T' should be almost 'invisible'.

 

[Compositepro]

You have to be very careful about ground loops being created when measuring powered circuits with an oscilloscope.

As already mentioned ultrasonic baths inherently have hot and null spots.

 

[VEBill]

"...when measuring powered circuits with an oscilloscope."

It would be rare to measure unpowered circuits with an oscilloscope. ;-) !!

 

[Compositepro]

Yes, I was not very comfortable with the wording, but I think I got the point across without spending hours covering all the details, which someone would have more quibbles with anyway.

 

[Erick D]

Thank you all very much for the help.

If I am understanding this correctly, per VEBill's comments I should try a High Impedance Prove and attach it directly to the BNC T? Also, I should match the impedance of the BNC T to that of the scope (RFstuff)? Or the HZ prove compensates for this?

 

[VEBill]

The whole point of scope probes is to measure signals without worrying as much about the effect of your measurements. That's why they typically have 10Mohm impedance; it's like they're not even there.

Ultrasonic is not RF, so the electrical wavelength is huge. Thus you'll not be bothered with the usual RF measurement gremlins.

I'd use the high impedance probe approach first, then you can experiement with 50-ohm approach if you like.

 

[itsmoked]

This chasing destructive/constructive is a total waste of time and I do mean TOTAL.

You don't want hot spots, then you need to move your parts around. If it's really bad then likely one or more of your piezo transducers or drivers are bad. I've had to fix these nuisances a dozen times. Worst product ever. They run around 50~80kHz.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

In response to 2nd thread...

This is a 5-minute set-up, max.

Use the BNC Ts. Use Hi-Z scope probes.

Yes, you'll need to adapt the probe to the open BNC socket on the T; that's why God gave us paperclips. Or those cute red and black BNC-to-Binding-Post adapters, but you may still need the paperclip...

All this presumes that the drivers are single ended and common ground. Isolated BNCs are ultra rare, so little risk.

 

[Erick D]

Thank you very much!