On Friday 01 April 2016 06:46:02 Erik Christiansen wrote: > On 30.03.16 17:13, andy pugh wrote: > > In the end, I fitted a different VFD which has a pre-written HAL > > driver. It also only has two connections for RS485, so is less > > confusing. I found a way to connect the dongle to the motherboard > > header: > > https://forum.linuxcnc.org/forum/18-computer/30675-on-motherboard-mo > >dbus-rs485-connection They are so cheap that I was prepared to go > > through a couple experimenting, but it works fine. > > Andy, > > That is an inspired solution to the ungrounded dangling-dongle problem > - well worth emulating. > > Incidentally, is that cable in the last picture twisted pair? Shielded > or no, is its characteristic impedance controlled? > > I wonder if the dongles have a 110 or 120 ohm termination, or you need > to add that yourself? > > It's usual to put a 100 ohm resistor in a ground wire run between > ends, to take up a difference due to leakage, but not cause big ground > loops. That's in data networks - I can't say for sure it's least > imperfect in a machine situation. > > Erik
I've not had to resort to that but its a good idea. Use a 1/8 watt 100 ohm resistor, and if the "ground loop" is strong enough to burn that out, then its safe to say that there are far more serious grounding problems in your present wiring config that need to be addressed as they are a shock hazard at best, and possibly lethal. In my latest build, I have a bare twisted grounding wire connecting all the machine frames together. But I maintain also a "star" ground config in that all shielded cables have the shield connected to one point in the "electronics" box, and trimmed back, no connection, at the far end of the cable. That connection in the electronics box is also its case ground and the machine ground is there also. > ---------------------------------------------------------------------- >-------- Transform Data into Opportunity. > Accelerate data analysis in your applications with > Intel Data Analytics Acceleration Library. > Click to learn more. > http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
