Problem with FFT

[deepen_solanki]

Ohhh.. Also, this data was acquired using the controller on myRIO.. Will it be better if I employ the FPGA module ?

[Brad_Turpin]

Hi deepen,

Better in what way?  The concern you've expressed (FFT amplitudes at higher frequencies) is related only to the data acquisition rate, which is variable in both controller acquisition and FPGA acquisition.  In either case you can change your data acquisition program to digitize data points at, say, 500Hz or 1000Hz instead of 76 Hz.

Brad Turpin

DIAdem Product Support Engineer

National Instruments

[deepen_solanki]

Hello Brad .. You have been really patient with my queries and i thank you for that 🙂

How did you calculate my sampling period by looking at my VI / data set ?
Also, I need to make sure i get to frequencies like 500-1000Hz .. what changes do you suggest in my VI that i can acquire and process that ? 

[Brad_Turpin]

Hi Deepen,

I looked at the values in your "Seconds" channel.  I took the last value and subtracted the first value from it and then divided by 3151.  I also calculated the delta times between each value of the "Seconds" channel and calculated the average of all the deltas.  Both ways gave me exactly 0.0139996826404316, which I rounded to 0.014.

You'll need to ask a LabVIEW support engineer for help configuring your acquisition rate to be faster.

Brad Turpin

DIAdem Product Support Engineer

National Instruments

[deepen_solanki]

Can I not change the 'wait' value on my loop where I acquire the accelerometer data ? Right now its at 2ms.

[Brad_Turpin]

Hi deepen,

You're not really acquiring accelerometer data with software timing are you?  If so, why do you have a wait time of 2 ms when your "Seconds" channel clearly shows values spaced much larger than 2 ms apart?  Typically you would set up acceleromter data acquisition with hardware timing.  In single shot mode you would acquire all the data to a buffer and read it once at the end of the acquisition.  In continuous mode you would read the buffer about ever second or so and append the results to a file you're streaming to.  Again, these are questions for a LabVIEW support engineer.

Brad Turpin

DIAdem Product Support Engineer

National Instruments