On 08/10/2017 11:09 AM, Les Newell wrote:
I have been chasing a noise problem on my lathe for some time now. I am using a 7i29 2kw drive and am getting a lot of noise on the encoders, even with filtering enabled at a pretty low frequency. I have tried just about everything I can think of. I made a simple near-field probe and did a bit of poking around. The 20kHz drive switching noise was strong pretty much everywhere. After trying various things I found a common mode choke on each motor output dropped the 20kHz noise down so it was pretty much undetectable apart from right next to the chokes. However I am still getting noise on the encoders. I have a spare encoder input on a 7i33 so I moved one of the motor encoders to that input. I am getting zero noise on that channel even though I extended the encoder cable to reach the 7i33 with 6 individual wires instead of a screened cable. Even with filtering disabled I see no noise. Unfortunately I don't have any more spare encoder inputs for the other axis.


Has anyone else had noise issues with 7i29 drives?

Are the shields of the encoder cables grounded at the encoder end? Are the encoders themselves grounded to the machine frame? Possibly different grounding of the machine frame, or isolating the encoders with plastic sheets and washers might help. (Don't forget the encoder shafts.)

Also, common mode chokes on the DC INPUT to the 7i29 might be of help.

Jon

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