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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