Delay in waveform graphs

[Miquel G.]

Hi

I want to simulate a delay. So, I've generated a waveform and I want to delay it a certain mumber of samples and compare it with the original waveform (for example a square waveform) in a waveform graph.

Have anybody made a similar VI?

Best regards

[becktho]

Hi

One way could be to generate a waveform with the required number of samples, with just zeros as y-values.
Then you could append this waveform and the one with the signal, using the function "Append Waveforms.vi".

Hope this helps.

Thomas

[Miquel G.]

It's ok, but...

What hapens if my waveforms does not contain zero values? For examle, imagine an triangular waveform. If I fill with zeros, the resultant waveforms will not be the original one delayed.

Thanks anyway

[becktho]

The delay, I would say, depends on t0 of the waveform.

Why do you want to compare waveforms? The better your problem is understood, the easier it is to find solutions.

Thomas

[Miquel G.]

Ok

I'm creating an didactic application in which I've to simulate the response of a system that provocates a delay in the input signal (for example, triangular or sinusoidal). Imagine a sinusoidal signal that you've to delay a certain angle (for example, 45º).

Thanks

[becktho]

Ok. So you could create a signal and change its phase.

Have a look at the attachment and change the phase-value. So if you would delay it, it should be the same as if you would set the phase-value to -45.

Thomas

[Miquel G.]

Ok,

But I want to ask another question.
Imagine you can't touch the phase of the original signal because it comes from other VI. You only have the connector of the signal generator. Is there any way to change their phase?

I hope you can help me

Thanks

[becktho]

If you just need the delayed signal to display in a graph, you could extract x/y-values, calculate the delay according to the x-scale and show it in a xy-graph so that the delay-time is without values.

If you also want values, try to get the parameters of the signal and generate a new one for the timedelay, which could again be appended with the original.

I can't give you more advie in a rush, because I never had to deal with phase-shifting on measured signals.

Thomas

[DFGray]

If you have a repetitive signal and an even number of cycles, you can "delay" the signal by taking an FFT of it, modifying the phases of each element based on the time delay you want, then taking an inverse FFT. This will work for any signal, but the edges get really weird if the signal is not repetitive and an even number of cycles. I have always tossed the ends of the modified signal when I have used this technique and not met these criteria.

[rpursley8]

This attached vi will change the phase of a signal, but signals with discontinuities (square, triangle, sawtooth, etc) are distorted from there original shape. Signals with only a few sinusoidal components work pretty well.

Hope this helps.