Frequency response and phase difference

[Petar2015]

Hi,

 I generate "Sine-Swept" with a function generator, which is the input of my device.

Then, I measure the output(vibration) via a photodiod (which is as voltage).

Now, I want to obtain FRF and Phase difference between these two wave (output and input).

In most of the examples, the input and swept has been generated by the software itself, but if the input has been acquired externally and also the swept has been done via a function generator, how would be the FRF?

I have installed "Sound and vibration toolkit", Could you please give me a heads up, that how can I do that?

In advance, I really appreciate your help,

Petar

[johnsold]

Use a second input channel to acquire the excitation signal (the output of the function generator). Then you have both the input and output of your device measured at the same sampling rate.  From there you should be able to apply the examples.

Lynn

[Petar2015]

Could you please let me know which example do you mean? As I saw, in the examples, the sweepable parameter was "Amplitude", but I want to sweep the frequncy, which is done by Function generator and don't see in the list.

[johnsold]

I do not have many of the toolkits, so I have a more limited set of examples.  In your original post you mentioned some examples that you had looked at. Do any of those show FRF?

The Frequency Response Function (Mag-Phase).vi (Waveform Measurements palette) accepts two input waveforms.  Wire the excitation to X and the output to Y.

Lynn

[Henrik_Volkers]

Look at the toolkit examples, they all capture the excitation and the DUT signal
Just cut out the DAQ AO part and replace it with your generator control.

However, when I read photodiode I think of nonlinear transfer functions 😉 , and depending of the method to calculate FRF you get different results due to nonlinearity ...

[Petar2015]

Thanks for your reply, Could you please explain your reply in more detail? what do you mean with "cut out the DAQ AO part and replace it with your generator control."?I'm new in labview so...:(

And, about the photodiode, I DON'T want to obtain the transfer function of a photodiode itself, The photodiode measure the vibration of another device, so its response would be the output.

I used the step of "Freq-Response", obtained the in and output, as I saw in one of the examples....but I don't know How can I include the sweep into the software setting..(I perform the sweep with a function generator which already generates the input as voltage"

Thanks

Petar

[johnsold]

Petar,

It is much easier for us to help you if you post your VI . Show us what you have tried. If possible save some of your data as default values on an indicator or control, since we do not have your hardware. Then be a specific as possible about what problems you are having. Telling us what you expect the result to be can be very useful.

Lynn

[Petar2015]

OK, I will, Actually I don't have the labview installed on my laptop, Give me a day, So I sent you the file tomorrow from the PC in our lab.

Thanks,

[Petar2015]

Hi,

I attached the project which I've recorded the data from DUTs. Also, I attached 2 snap-shots of the project, in case of the project file couldn't be launched.

I have connected the signal from a function generator to "ACH0" channel, and performed the swept-Freq in the output signal of function generator. (Red graph in 1st chart). Please note that the swept sine wave is generated via the function generator itself...NOT VI

The generated signal by the function generator is the input, which derives the oscillation of a drop,

A photodiode measures the oscillation of the drop via laser-scattering by drop vibration. SO....the signal generated by the photodiode is the "Response"....(white wave in 1st chart)(connected to "Ach1" channel.

Now, I want to obtain FRF, which the input is the signal generated by the function generator, and Response is the output of the photodiod'

As it's seen in the files...the FRF and phase difference is n't what is expected, also the coherence between in and output is zero!

Please help me out with this problem...

Thanks

Petar

[johnsold]

What is seproj? Are you using Signal Express?

Lynn