FFT Frequency Resolution vs. Graph Update Rate of a Vibration Signal

[chrishassan]

Hello,

First, what I know:

The frequency resolution (Hz) of an fft is 1/acquisitionTime (e.g. if 2 seconds of data are acquired, the frequency resolution is 1/2s = 0.5Hz).

What I'm Wondering:

Let's say I'm displaying an acquired signal on a graph and freq res = 0.5Hz.  The graph update rate is therefore approx 2sec.  This may appear to be an application with a problem from a user's perspective.

Can I increase the update rate?

It seems that with vibration data (i.e. mostly non-periodic) I could create a buffer that is 2sec long.  The first data acquisition sequence will fil the buffer with 2sec of data.  Then I could just acquire something shorter than 2sec of data (let's say 1/4sec).  If I am acquiring data continuously and I push the 1/4sec of data into the front of my buffer then perform the fft again, I have effectively increased my graph update rate to 1/4sec and my users think I'm great.

Can anyone shed any light on whether or not (why/why not) this will work?

Thanks for your time,

Chris  

[preston_johnson]

The best tool NI provides for your application is the Zoom FFT.  This allows you to specify the span (frequency range of the FFT) and the zoom (the delta f such as 0.5hz) in the FFT.  The Zoom FFT has a built in buffer, called overlap and allows you to set the overlap so that it updates at the appropriate rate, event though you may need many seconds of data to get the delta-f in the FFT you are looking for.  We package all this and manage units to display the correct units for power density, power, linear, magnitude, rms, 0 to peak, peak to peak, etc.  We even provide a express VI for the zoom FFT and it is also part of the Sound and Vibration Assistant, requiring no programming at all.

https://www.ni.com/en-us/shop/product/labview-sound-and-vibration-toolkit.html

[chassan]

Preston,

Thanks.  It sounds like this is exactly what I'm looking for.

Best Regards,

Chris