How to arbitrate a "delta t" for chart.

[geovane]

HI,

sorry but my English is not good.

I'm acquiring data from serial port, but my available data have just the amplitude (Y-axis).

I know the delta t is 2 miliseconds.

How to arbitrate de delta t to a Chart?

Can anyone help me?

[altenbach]

Set it via the properties dialog for the chart. (Another option is a property node, but make sure to only write it only if needed and not with every iteration)

[geovane]

Which property should I set?

[altenbach]

Try "x-scale..offset and incrment..increment" or similar. (Sorry, posting via phone)

[geovane]

Can I do something similar to calculate the power spectrum?

[geovane]

Because my input signal is 500 Hz and the power spectrum is not showing the right value!

[altenbach · Accepted solution]

You don't need it to calculate the power spectrum, just to dispay it and assign frequencies to the array elements. You can calculate df from dt and N.

[Nihil]

why not use "build waveform"?

since you'd have the array of data, and knowing the dt, one could just re-build the signal?

and for the FFT i usually use the express FFT...

[Matt_Dennie]

If you:

1. Build a waveform ("Build Waveform" function) from your time-series data, and
2. Assign 2-seconds to the "dt" waveform component, then
3. Use the "FFT Power Spectrum" VI from the "Waveform Measurements" pallette to calculate your specturm,

Then you can wire the output directly to a Waveform Graph and the delta frequency and frequency range will be automatically correct!!

[geovane]

I don't use "build waveform" because I acquire the data one point at a time.