Dynamic Signal Acquisition

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SV swept sine

Hi,

 

I am using SVXMPL_Getting Started with Swept Sine (DAQmx).vi example from sound and vibration toolkit for testing the bandwidth of DUT, and for a particular device i am supposed to obtain -90 deg phase at 32.75Hz and -3 db magnitude at 33.75 Hz but i am not getting these values i am attaching the obtained values as png file, the values are totally different the phase itself starts at -64.457... and it decreases from there i dont even see values nearer to -90 its the same issue with magnitude i am not even getting approximate values using this application, i dont understand what is the problem i have tried to change the terminal config. but no use pls help me solve this issue and also

 

the response is taking too long how can i increase the speed of the vi......i have changed settling time and cycle , intergration time and cycles to increase the speed i think this is making difference in the phase and magnitude is there any other way i can do this and get correct values

 

pls let me know if you have any questions thank you in advance...........

 

The DAQ i am using is USB 6215

Start frequency 35Hz

Stop frequency  0.5Hz

Number of steps 70

 

 

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Hello there,

I'm not aware of any particular reason that the settings you are using in that VI would cause you to get such invalid results.  You might want to try a few tests, the first I would suggest would be to take your DUT out of your setup, and connect your output channel directly to the two input channels.  You should see your phase at (close to) zero over the entire frequency range. 

 

You probably want to use differential for the terminal configuration.  Make sure you are connecting your signal+ and signal- to the proper terminals on your device.

 

Since you are sweeping such low frequencies, the sweep will take some time.  Things you could do to speed up the measurement will probably require you to make trade-offs with accuracy.  Things you could do to make it run faster:  continue to lower settling time/samples and integration time/samples, lower the number of frequency steps, or change the frequency spacing to linear.

 

Also, from your attached image, it doesn't look like you got mag and phase values at the lower frequencies.  Did you take a screenshot while the VI was running, or maybe did you get an error?  Have you modified the block diagram of the example at all?

 

-Alan

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