Multiple Phase values at one frequency

[samtha]

Hi,

I have done the frequency response analysis for a device using the frequency response example from sound and vibration toolkit and i get multiple

phase values at one frequency how can i reduce it to one value without any error i am posting the result from the experiment please check 

and give me suggestions are the stimulus and response phase values supposed to be like that???? 

[rpursley8]

I guess if the acquired signals are low level signals or acquired in a noisy environment, then they can have large variations in phase.  You probably need to average several acquisitions in the time domain before getting the frequency response.

[MattBradley]

Not sure I understand.  Are you saying that when you run it multiple times, you get different answers OR are you wondering why the phase is different at different frequencies?  The plot you have looks pretty reasonable.

[samtha]

 Hi Matt,

I mean to say for one frequency value i get many phase values for ex if u look at the screen shot  Freq resp results.JPG (260 KB) we can see for at frequency 8Hz i have 14 phasevalues why do i get like that.......even i thought i have to take average but there is too much of variation and also are the phase values supposed to be like that....

[rpursley8]

Don't look at the phase of each signal, that will change unless the acquisition is synchronized in some way.  It will be the difference between the phases that should average to a specific value.  Am I telling you things that you already know?

[samtha]

 Hi Matt,

I mean to say for one frequency value i get many phase values for ex if u look at the screen shot  Freq resp results.JPG (260 KB) we can see for at frequency 8Hz i have 14 phasevalues why do i get like that.......even i thought i have to take average but there is too much of variation and also are the phase values supposed to be like that....

[RavensFan]

SK,

You have serious problems in your File.VI.  Why are your writing to your file and then reading it right back?  Worse, there is no guarantee that the File write will actually occur before the File Read.  You have a race condition set up there between those two Spreadsheet File VI's.

If you want to maintain a history of whatever has already been written to the file, you should be building it into an array and storing in a shift register.  Even if your File.vi would by chance work the way you want it to, storing data in the file system is much slower than maintaining your data in memory.

As for your while loop, it is going to run as fast as it can with respect to all the functions occurring inside of it.  Is it possible you are getting 14 iterations of that while loop for each frequency step that is occurring?

Message Edited by Ravens Fan on 07-25-2009 01:35 AM

[samtha]

Hi,

yes i am talking about the phase difference only how do i reduce it to one value automatically w/o taking the avg.