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PLL

Hello,
i want to implement a Power Quality Monitoring system. For this project a PLL is nedded!Can anybody help me to understand the role of
PLL in this project!I Know that i have to use it but i cant understand why!
I hope you can help me!
thank you!
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You will need to explain the specifics of the project to understand exactly where the PLL plays a role... check out this knowledgebase titled What is a Phase Lock Loop (PLL)?, it might give you a quick reference on how NI uses it.
 
I don't know the specifics of the Power signal you are trying to check its quality, but if that signal is a PWM or something similar then I can see how you need a PLL to synchronize to it and take data acquisition measurements in order to compare the signal to a quality standard.
Nestor
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Thanks for your answer.
To be more specific....the input signal is sinusiodal or distorted sinusiodal periodic 50Hz. I made a PLL for this signal in a FPGA. IN addition this signal goes through an A/D converter and goes into the FPGA too. Now i want to do an FFT for this signal in FPGA.What is the role of PLL in all this??How i use it??and why??
I know what PLL is...i know that i have to use it...but i dont understand why i have to use it and how??I read somewhere that is for synchronize the sample rate with the input signal!
If you can help me..
Thanks anyway!
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Please note that I'm no expert on that field, but my guess is that if you are trying to check the signal quality of a 50 Hz sinusiodal wave, you need to compare it to another 50 Hz sine wave that you know is "perfect". In order to accomplish this I would generate a pulse train whose rising events will be tied to a specific section of the input sine wave cycle, lets say, crossing 0 V from low to high. That is, the 0 V crossing would trigger an active high for my pulse train and then I can catch every single cycle of the input signal... this pulse train would be the signal for the PLL... the "perfect" sine wave is being generated perhaps in the FPGA but is synchronized via the PLL to the input sine wave using that pulse train that I'm talking about...

This would be my initial thought on how to attack that problem, I hope it helps.

Nestor
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