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Convert to square to detect phase shift


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Hi,

Im quiet new in labview, using version 8.6.

I need to develop a system to detect a phase shift of vibration between a case and the rotor. (of a washmachine)

I simulated the signals in labview and the upper "pulse measurements.vi" quotes:

"Error -20308 occurred at an unidentified location

Possible reason(s):

Analysis: The waveform did not cross the mid reference level enough times to perform this measurement.

Check the signal length, reference levels, and ref level units.Analysis:

The waveform did not cross the mid reference level enough times to perform this measurement.

Check the signal length, reference levels, and ref level units."

If i attach a signal directly to the upper pulse measurement vi then it works fine.

if i run with the converted signal he gives the error, but i can continue

But i need to measure from 3Hz, now it's still 20

If i place it on 3Hz he refuses everything.

Hope someone know's a solution.

Download File:post-15503-1242203275.vi

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You don't have enough data points above and below the threshold to complete the "Peak Measurement" analysis.

Either

1.Change the "percent level settings" method from "Auto Select" to "histogram" to force that method

or

2. Change the threshold levels to something like 40%,50% and 60%

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QUOTE (Tubi @ May 15 2009, 01:49 PM)

Well the latest example you supplied seems to work fine. I changed the variables on the front panel and it didn't complain. Are you saying that it works in simulation but not on the hardware?

If this is the case. It might be useful to capture the data from the machine to a file and run that through the simulation. Then w can all see and investigate the differences.

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QUOTE (ShaunR @ May 15 2009, 03:18 PM)

Well the latest example you supplied seems to work fine. I changed the variables on the front panel and it didn't complain. Are you saying that it works in simulation but not on the hardware?

If this is the case. It might be useful to capture the data from the machine to a file and run that through the simulation. Then w can all see and investigate the differences.

I didn't runned it on the machine yet, but just simulated it.

If i lower the frequency then he gives the error again about the reference levels.

Don't understand why it works on 20 Hz but not on 3Hz

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QUOTE (JasonXCX @ May 18 2009, 03:07 PM)

Intresting,

I use a accelerometer of analog device (ADXL103)

a 1,7g single axis accelerometer.

Is very usefull.

I read the signal with a daq to labview.

Then i simulate the signal identical on the measured one.

And when the simulation works i test the real signal.

works fine now.

thx for the link, defenetly will try it today.

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QUOTE (Neville D @ May 20 2009, 07:22 PM)

I'm not sure what you mean but if you want to "unwrap" the phase so there are not discontinuities at +/-180 deg, search for Unwrap Phase.vi.

N.

I know that vi exists but it doesn't work for a square signal.

So i can not use that vi.

Now i measure a phase shift that sometimes is more than +/-180 deg.

not errors but more like ==> (340° = -20°) it needs to stay between the +/-180°.

because now i can not put this in a graph in excell or something like that.

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