Ultrasonic high speed distance measurement

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maximum flow, the impeller is so to say sucked into the flute (outlet), so it stabilizes the impeller. On the other hand, when the flow is cut off (t he impeller is just rotating the fluid), the impeller control is less due t o the presence of a lot of turbulence (simplified explanation)

I have access to the current, but fluctuations in the current won't tell me if it is the impeller that is moving i Z direction

Yes, but again, I need to pin point if the impeller is moving up and down. The rest of the system will disturb the measurement

Like above. That could just be turbulence

Cheers

Klaus

Thanks, that's what I was looking for. Will give them a call :-)

Cheers

Klaus

Looks promising:

But they do not exactly state the upper frequency, but probably high enough for my needs :-)

Cheers

Klaus

I don't know what pressure, but can you drill a small hole through the housing and insert a needle to feel the impeller shaft centre? Ok, there's some leakage, but you say the housing is just for test purposes.

Cheers

Do you know those guys Joerg? We resell/market some of their stuff here in the US. AFAIK it's all liquid or solid based... no in air ultra sound.

George H.

I don't know them. My background is medical ultrasound but I have moved more towards oil/gas, industrial and aerospace now.

That seems to be what Klaus need.

The noise floor diagram indicates that it's in the hundreds of kHz. I'd be more concerned with stability close to DC which I assume you need. They should be able to answer that upon request.

Make a temporary housing out of perspex so you can see what is happening.

Great idea. With a strobe locked to the rotation and having adjustable trigger delay.

Cheers

We have that already, made of SLS.

But that is really difficult to translate into a spectrum, which I need in order to quantify if the problem is remedied between tests

Cheers

Klaus

Just an "off the cuff" idea: What if you spray-coated the front face of the impeller (towards that plastic window) with flame spray or some other conductive paint? Such that the paint contacts the shaft for a somewhat suitable RF ground. That is now one side of your capacitor. Stick copper tape to the plastic window and this becomes the other side of the capacitor. Run the pump with thin oil that has similar viscosity as water or whatever else the pump usually handles. Now hook the cap to an impedance analyzer, an oscillator or a generator-scope setup, whatever is available. When the impeller begins to protrude this will cause the capacitance to increase and that could be measured. You could obtain a graph over time, for example while varying head pressure and all that.

It'll be in the single-digit picofarads but that is something I recently used for measurement using just the sound card of a PC plus the software Daqarta. The phase recorder over time part is a bit funky but I (usually) could get it to work and the method is really sensitive.