What it boils down to is not the VFD but something in the DC or low voltage circuits. I don't have a modbus problem but rather a sserial problem.
Thanks On 1/4/2016 3:00 PM, Rafael wrote: > When nothing else works, it's wise to go back to the beginning. After > so many suggestions, recommendations, and disagreements we have not > solved this problem since last year. > > While grounding could be a major issue, it's not necessarily so in this > case. As long as there is star wired ground. Besides ground loops don't > always add up, sometimes they subtract too. Of course, we are not at the > broken system so troubleshooting is obviously difficult. > > On 12/26/2015 07:16 AM, John Thornton wrote: >> I just checked the ground to housing on the VFD filter, VFD, computer, >> and the smaller filter and they are all internally connected to ground. >> The VFD is controlled via modbus so I don't know how to check that cable >> (which is just a phone cable with a phone jack on one end and a DB9 on >> the other end to connect to the computers serial port, it's a Automation >> Direct cable not home made. >> >> Is injection to the mains coming back to the machine somehow? >> >> JT > Troubleshooting was mostly focused on ground and wiring so far. Modbus > is where the (noisy) action is so it's the most obvious place to start > troubleshooting. > > Not being familiar with modbus I decided to do some reading on it. > https://en.wikipedia.org/wiki/Modbus > https://en.wikipedia.org/wiki/RS-232 > > If I understand it correctly, there are 3 physical means to carry > modbus: RS-232, RS-485, and ethernet. RS stands for Recommended > Standard, which never became a real standard as far as I'm concerned. > I've seen RS-232 implementations for mainframe and PC computer > peripherals and ham radio ranging from ±25V to ±12V and what's most > common today, ±5V. > > RS-232 is relatively immune to noise, for speeds we are dealing with > here, as long as one side of shielded cable is grounded. We used to have > cable runs between mainframe computers and terminals in other buildings > with (to a degree) different ground and no major issues. > > After some search, I ended up reading this document, Modbus For Field > Technicians: > http://www.modbusbacnet.com/includes/pdf/MODBUS_2010Nov12.pdf > see pages 29 and numerous pages dedicated to RS-485 issues. > > I am assuming that your implementation is based on either RS-232 or > RS-485. At this point it might be worthwhile to look into VFD "black > box" to see how exactly it connects to the outside world. > > Time to check: > - (HW) drivers, ICs, transistors, local caps, voltages [1], > - configuration (parity, etc.), > - use RS-232 breakbox and check signals quality with scope > - try different RS-232 port on PC or replace it if necessary. > - any related jumpers, if any > > [1] optical connection protects you from different voltage levels but > that was not your first try I think so the port on PC side could be > damaged if the VFD side uses 12V for example. It depends on how old the > VFD is. > > Unknown: > - was VFD/modbus fully functional before rewiring BP? > - What says the VFD maintenance manual? > - Can you run standalone tests on VFD? > > How about replacing the DC motors with large resistors and run the > tests? One by one or all. Are those brushless motors? What's the noise > around motor wires with a motor or with a resistor? > ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
