How to create the power spectrum and bicoherence graph from OP and PV analog trends

[Amily2201]

Hello

I am the beginner for labview and I am doing my project with labview. Initially, I insert the data from excel to build the OP (Control valve output) and PV(Process value) with sample. And then, I would like to create the frequency and amplitude from these graph for building the power spectrum and bicoherence graph. I already seen the bicoherence analysis.VI in find example but I dont understand and I got the error as picture. So, are there anyone can help me for these question?

1. Is it right or wrong value in frequency and amplitude?(please see in my program as attachment)

2. Can help me to build the power spectrum and bicoherence graph?

[NIRebecca]

Hey Amily2201,

From the looks of the error it's a mismatch between your Sampling Rate and Frequency. 

You've put 0.0077 samples per second as your sampling rate. According to Nyquist theorem the minimum rate at which a signal can be sampled without introducing errors is twice the highest frequency present in the signal. Hence your frequency needs to be smaller or equal to 0.0077/2. 

You could try putting a probe on the Frequency coming in to see what you're actually reading, and adjust your sampling rate accordingly. 

Hope this helps, 

Rebecca

[Amily2201]

Thank you Rebecca. Now i try to apply the bicoherence analysis.VI in find example. I replaced the frequecy 1,2 and amplitude 1,2 from data that i obtained from my PV-OP graph and I replaced frequency 3 = f1+f2 is it right?

and i dont know what is the amplitude 3 ? and what is the suitable setting parameters in my case?

Thank you inadvance for your help.