On Sunday 03 April 2016 13:36:23 Danny Miller wrote: > Well, if you have 2 differential wires with a simple optoisolator at > the far end, ground noise/ground loops would have no effect > whatsoever. You don't need a ground. There would be no place to put a > ground. There are no common-mode issues. The slave device's ground > could be +300VDC above the master's ground. > > However, RS485 doesn't spec that way. The ADAM isolator box I have > probably has optos inside, but has to make an RS485 output- which is a > low-voltage DC differential in relation to a known ground. > > Danny
To me, considering the low voltages rs-485 uses, compared to the light it up voltages the opto's need, is a total non-starter. The RS-485 would have to be amplified to a several volt differential, at the source, and that used to drive a laser diode, and that sent down an optical fiber to a diode on the other end of the fiber, and that diodes output then level translated back to RS485 differentials. Such a circuit could survive anything but a cut fiber or a power failure. 100kv of EMP from a nearby lightning strike wouldn't bother it. > On 4/3/2016 5:21 AM, Nicklas Karlsson wrote: > > On Sat, 2 Apr 2016 11:34:25 -0400 > > > > Gene Heskett <[email protected]> wrote: > >> ... > >> Given all that, I do not see how, in a noisy industrial > >> environment, or even here at the Heskett's home camp, it can be > >> error free unless an optical translator, bidirectional, is used at > >> BOTH devices terminals. > > > > I am not sure about the optical translators. Why however I can't > > tell for sure. > > > >> ... > >> > >> The question then seems to be, is who makes these rs485 to opto > >> fiber (or even to RJ45 jacks & cat5 or cat6 cable since it doesn't > >> have this common mode noise problem that I am aware of), > >> bidirectional translators and at what cost. > > > > Ethernet which use the RJ45 connector have tranformer for > > insulation. I have experienced communication errors over Ethernet > > then communicating with inverter. > > > > > > Nicklas Karlsson > > > > -------------------------------------------------------------------- > >---------- 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 > > ---------------------------------------------------------------------- >-------- 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
