Ultrasonic high speed distance measurement

Is the shaft metal? Maybe a coil wound on or near the housing would change inductance.

It is a ceramic shaft...

But I can glue a metal plate onto the shaft end. Impedance measurement migh t work, good idea ?

a Doppler shift can be integrated from velocity to get displacement if you had the appropriate equipment.

Or with the appropriate microwave network analyzer be able to find the standing wavelength of the displacement from the antenna reflections.

Den tirsdag den 17. januar 2017 kl. 22.47.25 UTC+1 skrev Klaus Kragelund:

something like this?

I am pressed for time, so I think that solution, although a nice method, will take to long to get working

Cheers

Klaus

On Tuesday, 17 January 2017 23:26:16 UTC+1, Lasse Langwadt Christensen wro te:

r. The pump is a wet-runner, so I cannot access the internals of the pump h ousing. The pump housing is made of plastic

the shaft, so effectively the shaft is moving up and down)

n measure the distance to the impeller through the plastic pump housing.

d output the distance at high speed, so I can capture the speed output in a spectrum analyzer to determine if the shaft is indeed moving?

ay have to low resolution. The advantage of ultrasonic is that the intermed iate medium is water and that probably has well known properties

roximity sensor to detect the capacitance change when the plate moves up an d down.

That's nice. So you mount the detecting coils to get minimum output and go from there.

I have a 3 phase stator that drives the motor, so I could wind another wind ing and measure the BEMF envelope of that winding. Problem is with BEMF mea surements, that the excitation from the inverter driving the main 3 phases on the stator will couple to the BEMF winding rendering it very difficult t o get good measurement

You idea is on the far other end, so disturbing fields are lower, and since I know the electrical frequency of the drive, it's possible to filter out any frequency in that vicinity (movement of the shaft if either subharmonic or harmonic of the electrical frequency)

Cheers

Klaus

I'm obviously missing something ultra-important here, but ISTM that if you measured the axial play in the bearings and assumed that (between gravity and the reaction force of the pump) it moves over its full range when the pump cycles, you'd be pretty close.

Cheers

Phil Hobbs

The action of the axial play is not constant. When the pump operates at max imum 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 (the i mpeller is just rotating the fluid), the impeller control is less due to th e presence of a lot of turbulence (simplified explanation)

Cheers

Klaus

The insides of the pump:

The pump housing is made of plastic instead, just for test purposes

Cheers

Klaus

It depends on how accurate you need to be, time sensitivity, your rental budget and test and measurement skills. But I would go with a 10GHz VNA.

Or a small magnet on the shaft and an external analog Hall sensor. Digikey stuff. But you'd have to calibrate it somehow.

Does it make enough sound to be detected and analyzed?

wouldn't you be better off using CT's inline with the drive coils?

strain on the pump due to fluid moving causes the up raise of current.

If it just sits there the current will be lower.

Also, why can't you use flow sensor in the stream?

Jamie

Den onsdag den 18. januar 2017 kl. 01.31.57 UTC+1 skrev M Philbrook:

at

nge

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)

afaict he want to measure the axial movement of the shaft not flow

seems like over kill just to detect if fluid is flowing or not, but if mechanical testing is being done then something on the lines of a LVDT can be wrapped on it using the stator as signal source to balance a stationary position.

The movement of the PM rotor sliding could be detected as a pulse, but if you use the AC field of the stator, you could get a constant output.

Having two coils around the motor section to pick up the weak stator field from end to end in a canceling form. Third coil around the two as the secondary. when the shaft inside displaces, it should unbalance the two primary coils and thus produce a small signal from the stator field.

We do something along the same lines but not with a pump, but the idea is the same.

Jamie

Sorry, it didn't send earlier today because of some transmission error.

You might want to talk to these guys, see whether their equipment can do it (probably can) and where it could be rented:

The mode to try would be "M-mode" where the positional shift of a reflector along a single ultrasound beam is measured at very high frame rate. So you could peel out vibrations and other effects. The Z-axis movement would need to be somewhat independent or at least not synchronous to the impeller blade echoes.

A Doppler ultrasound device from a medical place could also work, even a really old one. In that case start running it in CW-Doppler mode.

A Kaman prox sensor from Kaman Sensors and a metal disk glued to the shaft end would probably work.

I've used them for similar jobs in mechanical prod dev work.