On Saturday 03 October 2009, Steve Blackmore wrote: >On Fri, 02 Oct 2009 15:24:24 -0400, you wrote: >>Page 5 and 6 show it but not at a good time scale, page 7 from the base >>thread sample shows it very clearly Steve. Noise. Until that is gone >> (and encoder A output could have a closer to 50% duty cycle too, I'd >> almost return that one in fact if its sealed and non adjustable), it >> isn't going to work, not even if we make sacrifices. :) >> >>I have to assume the encoders cabling is shielded, and the shield ends at >> the encoder so there is no connection via the shield to the machine by >> way of how the encoder is mounted and driven. That would be what we call >> a ground loop, and that is usually a no-no. > >Thanks Gene, that gave me clue and I found it - The encoder cable had a >strand from the shield touching the plug at the controller end.
Ideally it should be connected solidly at the controller, and not connected at the encoder end unless the encoder mount is isolated from the machine. Shielding carried into the encoder housing is a good idea, as long as it doesn't have a connection to the shaft or the mounting. All shielding should be connected to the controller. I ran a piece of 12 gauge copper wire around the outside of the box I made for my xylotex controller, it is tied to the - rail of the motor psu, all motor cable shields are tied to it, and of course the ground wire from the computers parport is also tied there, all solidly soldered with a silver bearing solder, 3% silver I think, the rest the usual eutectic blend. Motor cables, and interconnect cables for the spindle VSR control (a PMDX-106, works great) are all in a microphone cable that Belden calls 'star- quad', which has 4 wires and a mylar foil shield covered with about a 96% tinned copper braid. Very good cable IMO. This sets up what we call a star ground system, where every signal ground in the system comes to one common point. Any currents that flow, because there is only one common point, cannot develop a stray signal due to the resistance or inductance of the ground because everything is referenced to that one common point, in this case about 8" of 12 gauge bare wire so there is room to solder all the shields to it. I think it works well, I have used an optical probe to scan surfaces as described by one of the guys here, several times and the biggest error is the sideways slop in my probe, it may flex or take up the slack in the slip tubing as it slides downhill on a curved surface. >Much, >much better now, but still has the odd glitch, from where I don't know. >disconnecting all the grounds didn't get rid of it. > >As for the 50% duty cycle, can't do anything about that other than >replace the encoder. > >But - running at slow speed it's MUCH better, and running my test 1.5mm >pitch test file at my normal 700 rpm it's not noticeable at all. > >Have a look at the difference :) > >http://filebin.ca/brcenc/encoder.pdf > > >Steve Blackmore >-- > >--------------------------------------------------------------------------- >--- Come build with us! The BlackBerry® Developer Conference in SF, CA > is the only developer event you need to attend this year. Jumpstart your > developing skills, take BlackBerry mobile applications to market and stay > ahead of the curve. Join us from November 9-12, 2009. Register > now! http://p.sf.net/sfu/devconf >_______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users > -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> Goals... Plans... they're fantasies, they're part of a dream world... -- Wally Shawn ------------------------------------------------------------------------------ Come build with us! The BlackBerry® Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9-12, 2009. Register now! http://p.sf.net/sfu/devconf _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
