As someone who has very little knowledge of the Modbus protocol you will have to bear with me on this one.

Does anyone know of any instances where a DCS would effectively turn off a port to a RTU but think it is still running? That is, all drives on the DCS are showing green and running, but in reality the RTU has lost all its TX and RX between itself and the DCS, and the drives have stopped.

We have changed all the hardware possible. RTU hardware and cabling, Modbus comms boards in the DCS (including the board carrier), we have even failed the processor over so that the back up becomes the primary, etc. The setup is pretty standard - DCS (Master) RTU (Slave/Master) Motor Manager (slave).

The DCS we are using is an ABB ADVANT. RTUs are Kingfisher PC-1 processor and MC-11 multi-communication module.

Any thoughts would be well received.

 

Yes. You can kill an Advant controller serial link.

If the MODBUS link fails, the ABB Advant Controller will set the status of the link to off, and will stop updating the DAT elements on the link. Your information becomes frozen until the serial link starts working again.

If you have then gone into the Database and changed port numbers or information on the MVI or DS database elements trying to get the link to work then it is possible you might have halted the PLC interface altogether. If you do this in an Advant controller you need to COLD start (ie load from a DUAP of a working system.)

MODBUS and other PLC interfaces in an Advant controller are hard to commission but are normally very reliable once they are started correctly. For this reason, if they stop working it is almost certainly a hardware error and you should never modify the interface configuration software.

If you have changed all of the involved hardware and the Tx light in the Advant Interface board is not flashing then the controller is not trying to establish comms.

First try to identify if you still have a cabling or slave problem by connecting the Advant serial port directly to a serial port on your PC or a MODBUS slave emulator.

Also, check for any error messages on the engineering station.

Finally, If you cant get the Advant controller to start polling (i.e. flashing the Tx light), then you may have to cold start the controller.

Sorry.

Rob

www[.]lymac.co.nz