On 01/04/2016 07:34 PM, Mark Johnsen wrote: > Bertho - What you state about the different power supplies is a fear of > mine as I have a +-15vdc Power supply for the Op-amps for the West-Amp > servos, an open frame type 24Vdc power supply, plus the 5vdc power supply I > added for the 7i77.
Many PSUs just makes it harder and the chances of "doing it wrong" a lot larger as well as inadvertent (read: potentially disastrous) things happen when you start to fiddle in the wiring to test one or another thing... > Also, I don't have my PC in a PC case, open frame w/ the 5i25 held in by > friction (i know, I don't like this either - need to bend a clamp). But, > the PC power supply also could factor into the ground loop equation. I > have mine mounted to the door of my enclosure. The PC PSU is almost certainly connecting 0V (DC) to the protective ground. That almost(*) always means that all other supplies need to be isolated from protective ground, or you will have a loop. Anyhow, all the PSUs make it a nightmare to track the 0V (DC) reference throughout and ensuring it cannot loop. Especially low-power (signal) connections are hurting badly if you loop it with a high-power (DC) circuits. (*) There are some narrow exceptions (ymmv), but don't bet your sanity on that. > I feel like it's really hard to trouble shoot because you have the 5vdc to > power the 7i77 and then limits, relays, etc are presumably run off 24vdc. > So, plenty of ground loop possibilities, especially w/ the encoders and > limits being wired up on the original wiring. Plus the addition of the PC > to the cabinet... You hit dead center here... It is a nightmare to troubleshoot. That is why you usually need to plan very carefully in advance (yeah, I know, good idea, but time is scarce). A few design guidelines: 1) keep high-power and low-power systems separated as good as possible (both AC- and DC-wise); 2) assure, in the low-power system, that you separate the high-speed-signal and the low-speed-signal parts as much as possible; 3) design using a star-shape. One center and from there to the peripherals. Interconnects on different star-legs usually/often need to be galvanically isolated to prevent loops. 4) test incrementally. It is much easier to identify the problem when it is detected when one (1) single and simple device is added. (However the cause can still be extremely complex due to interactions.) -- Greetings Bertho (disclaimers are disclaimed) ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
