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3 phase Signal conditioning

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PauloSherring

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Hi guys!
I want to build a 3ph line - both wye and delta wiring - signal conditioner, for hooking up on a National Instruments cRio system. According to simulations on Orcad, I could use diff amplifiers with high input resistance (1M) and then trim the signal for calibration.
But I am not sure if this is acceptable, since it might create ground loops that may introduce errors - and the aquisition system is costly and I dont want to mess it up. Is there some reading you guys could point me out?
The objective is to analyse energy quality parameters, so, RMS chips are of the table.

Thanks in advance.
Paulo Sherring.
 

ZekeR

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Paulo, can you post the schematic of the circuit you are envisioning? I am having trouble seeing specifically how a difference amplifier could be susceptible to ground loops, or even create them.

Difference amplifiers are often used specifically to avoid ground loops. If you want to test the circuit's behavior in the presence of ground loops, you can simulate them (by defining two different "grounds," and introducing a varying voltage source between them).
 

PauloSherring

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ZekeR, I did as you suggested and it did, in fact, eliminated any voltage fluctuation. It is something I should have known, but I completly ignored.
Thanks for the in sight. The circuit diagram is attached.

Now, what about the CM voltage? Should I worry with it somehow?

Paulo Sherring.
 

PauloSherring

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By the way, mismatches in those resistors at the imput stage will introduce measurment errors - ie will amplify CMV and . Is there a CI that have the whole thing implemented in silicon chip, with highly matched pairs?
I just realized that this error won't be repairable with futher adjustments...
If the CMV is DC, I could simply high pass the signal, but, probably wont be dc...
 

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