peak search frequency error

[Ronster]

I am recalling frequency domain spectra and performing a peak detect.  The frequencies that populate my output window are more than double the frequency I know they represent.  For example, testing a 2 pole motor, the speed without load should be 3600 cpm.  The peak detect program returns a value of 7371.43 cpm!!!  It can't be window error, not at more than double.  Anybody know what's going on here?

[LaurenLL]

Hi Ronster,

Are you using the Power Spectrum vi located in the Frequency-Domain section of the LabVIEW function palette?  Have you verified that the actual values being sent to the peak detector disagree with the outcome you are getting?  It might be useful to create an indicator before the peak detector in order to have values to compare against.

The peak detector has a location, amplitude, and second derivative output.  Which one are you reading?

Regards,

Lauren

[Ronster]

No.  I am using the 'XY graph' from the peak detection example vi. 

[LaurenLL]

The peak detection vi still uses the peak detector function, so it may be worth looking into the actual inputs you are putting into it using an indicator.  It should just run the data you are inputting and locate points that are above a specific value.

Are you using the Peak Detection and Display vi?  If so, have you made modifications to it?

Regards,

Lauren

[Ronster]

I copied the 'guts' of the peak search vi and then pasted into my data recall vi.  I wanted to keep the 'red' threshold cursor.  That works fine!  It's just the frequency values.  The peak values are right on.

Ron

[LaurenLL]

Hi Ron,

From the example I am looking at, I do not see any functions that read the frequency.  The peak detector itself only outputs the location, amplitude, and second derivative.

How are you acquiring the data and how are you reading the frequency?

Regards,

Lauren

[Ronster]

The  data I am looking at is a saved file with six fft spectra, so the frequency data and amplitude data already exists.  I am just pulling it back out and want the peak search to do it's thing.

[LABJAHO]

j'ai un problème quand je lance le driver d'un oscilloscope une erreur n°3 : "memory.cpp", ligne 483 qui apparait je ne sais pas c'est quoi le problème si vous pouvez m'aider à resoudre ce problème merci...

[LaurenLL]

Hi Ron,

So if I am understanding you correctly, you are reading the frequency as the location of the peak amplitude.  Are you only receiving one value that is much larger than the expected value?  Have you tried taking a look at the graph itself prior to sending the data into the peak detector to see where the faulty data may be coming from? 

It may be worth posting the data you are working with so I can try playing around with the Peak Detector vi and see if I can reproduce your issue. 

Regards,

Lauren

[LaurenLL]

Hi Labjaho,

For better support of your issue, you should probably try posting on the French forums.

Regards,

Lauren