On Tue, 8 May 2018, andy pugh wrote:
Date: Tue, 8 May 2018 12:20:53 +0100
From: andy pugh <bodge...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: [Emc-users] Ferrite on a shielded cable
I have concluded that I have a problem with noise from my (shared by 4
drives) servo power supply.
The STMBL drive controlling the 4th axis suffers from CRC errors with
the smart-serial control signals and shuts down.
By the simple expedient of running it from a separate PSU this problem
seems to be eliminated.
(It ran fine all night yesterday).
I don't see this as a good long-term solution, so I want to get rid of
the noise in the DC supply. This seems like a job for a choke, but the
cables have a braided shield.
Should the shield pass through the choke, or should I strip the area
where the choke is installed?
--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
?? George Fitch, Atlanta Constitution Newspaper, 1916
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At the frequencies involved, your entire "ground" is nothing but a big tapped
autotransformer. For our experience with the 8I20 we found the simplest thing
to do about EMI was to put a large ferrite bead over the 3 motor U/V/W wires.
The problem as John K mentions is that you have say 350V square waves driving
the motor wiring and winding capacitance so you get current spikes at each
square wave edge, and these spikes have very large amplitudes. This causes
severe ground bumping in the motor drive (perhaps exceeding the serial links
common mode range) . By adding a large ferrite bead over the three motor wires
(a common mode choke), you reduce the amplitude of these current spikes and
hence reduce the ground bumping in the motor drive.
Peter Wallace
Mesa Electronics
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