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Old March 13th, 2018, 10:19 AM   #16
keithkyll
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Quote:
Originally Posted by milmat1 View Post
...Something I have discovered recently is that during the install none of the 15 + VFD cables are properly grounded at the motor end. I used Belden 295___ Cables and the installers did not connect the shield at the motor end. I feel like that is likely trashing the entire ground system with PWM harmonics...
That's what I see on your 'scope photo. Concentrate on the source of the noise - the VFD cables. You've got far too much RF noise to ever hope to cure it by addressing encoder cables.
Ignore the 60 Hz reading on Fluke. Doesn't mean much. The 'scope is your best friend. Trust it above everything else.
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Old March 13th, 2018, 10:50 AM   #17
Mad_Poet
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I know this sounds stupid . . .
But is there any chance the motor wires and the signal wires are ran in the same conduit?
(Or even in the same raceway?)

Poet.
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Old March 13th, 2018, 11:21 AM   #18
danatomega
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I once chased a noise problem with a vendor for 4 hours.
We gave up for the moment as we went to lunch.
He said "man, seems almost like there's a transmitting tower blowing up the signal".
I pointed out the window and said "3 WHIO am towers right there".
He added a couple caps on the signal wires and it fixed the problem.
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Old March 13th, 2018, 11:28 AM   #19
danatomega
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You are using VFD cable with overall shielding in this installation?
And shielded encoder cable?
Are any connections terminated in junction boxes or are they a straight run?
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Old March 13th, 2018, 03:40 PM   #20
JordanCClark
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I see the transients neatly lined up on all the traces. If it's also on the encoder power, I'd start with a bypass cap there.
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