On Sat, 2007-10-20 at 13:01 -0500, Jon Elson wrote: > Kirk Wallace wrote: > > > > The whole idea of the differential boards where to reduce the > > susceptibility of the system to noise, but the boards themselves seem to > > make the effect of the noise worse. > > > What are you using for the differential driver chip? Is it > totem-pole output or open-collector?
I am using the DS26C31 http://www.national.com/ds/DS/DS26C31M.pdf > > I think I need to place ferrite beads or other type of filter on the VFD > > inputs and outputs and then revisit the oscilloscope. I don't have much ...snip > really helpful. That represents a classic ground loop situation. > > Don't put capacitors on the VFD output terminals. A series > inductance can be helpful, but is not guaranteed to help. > A line filter on the input is much more helpful, as capacitors > can be used there. I am using a commercial line filter made by > "Filter Concepts", probably a Mil-spec unit, rated at 15 A, for > my Bridgeport spindle. It is likely overkill, a 6 A unit would > most likely handle the 1 Hp fine. I have no filtering, and no > shielding, either, on the VFD output. I do have a ground wire > in the 4-cond cable, tied to the VFD frame at one end, the > machine frame at the other. The line input filter solved the > noise issues I was having, with the computer monitor and my > computer-controlled air compressor, which was only running off > the same breaker panel. That line filter came out of my junk > box, no idea what it came out of. > > Jon Is it something like this: http://www.eastek-intl.com/images/PreoSeriesER.pdf ? -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe Bridgeport mill conversion pending Zubal lathe conversion pending) ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
