Modicon Help

[ICTechs.com 0]

Hello all, One of my forum members posted this issue with a Modicon PLC: Modicon 984 Compact PLC's w/265 CPU's Troubleshooting Tips Sought: We have a Group Schneider/Modicon Compact PLC-984 with a model 265 processor. The PLC is on a small 3-node network communicating through the Modbus 2 ports to a Bridgemux multiplexer. It is running some (unknown) version of Concept ladder logic. We have intermittent communications errors and "Master PLC Fault" alarms that come and go in 2 to 5 minute cycles; even when there are no comm or PLC faults, the CPU will not function. It's a long story, but suffice it to say that swaptronics is not an option here; the 3-node net is for absolutely critical equipment, and whoever wrote the control code set it up so that any interruption in communication disables the other PLC's (EXCEPT in the weird case of the failing 984; when it is in its intermittent comm fail and/or PLC fault condition(s), the rest of the Modbus 2 net works just fine!). ANY tips and/or enlightenment appreciated! This one has stumped the "experts"! http://www.ictechs.com/showthread.php?p=480#post480 Edited 29 Nov 2006 by ICTechs.com

[Crossbow 295]

Is this 3 Compact PLCs or a PLC and other devices? My first question would be why using the bridgemux and Modbus 2 ports, when Modbus Plus is faster and more reliable, and built into those CPUs. The bridgemux is an expensive extra piece of hardware. As for the comms, the problem is probably something in the code in the PLC. If one PLC stopping or comm loss causes the others to stop, it's being stopped via a program. The PLC by default doesn't care if anything is talking on the serial ports or not.

[ICTechs.com 0]

Modicon 984 brain-cracker Crossbow: Thanks for your reply. We are coming to the conclusion that the PLC comm faults are indeed software-originated; the maddening thing is that we cannot talk with, upload/download, or even identify the current version of the Concept inside the failed PLC (the OEM has had several turnovers in personnel since original installation some 7 years ago, and it would be a kindness to report that they are not exactly customer-service oriented). As for the configuration, the Modbus+ channel is dedicated to an outside Modbus+ network that includes a number of other PLC's (all Quantums), and the Bridgemux reports to this larger Modbus+ net as a stand-alone node that includes data from all 3 of the PLC-984's. Quite a pickle! We're probably looking at dropping back 15 yards & punting, purchasing a brand-new Modicon Compact (whatever the current version is) for all 3 pieces of equipment (ozone generators), and rewriting the ladder logic based on old hard copies of the original code. Anyway, just fishing for whatever help we can muster, we are bleeding money to fly people into and out of the foothills of the Cascade Mountains (we're a bit off the beaten track), only to have them all shrug their shoulders & go "beats me". Again, thanks for the reply. R

[Crossbow 295]

Some older versions of Concept (like before 2.2) did not allow for uploading. In order to upload IEC code a copy of the raw uncompiled code must also be stored in the PLC, raising the amount of memory required. If this was in fact written with an old Concept, you're not going to be able to upload it. If it is written with a newer version, there should have been the option to include that code in the download, but it's unchecked by default for size considerations. Either way, sounds like rewriting is your best bet...

[TimWilborne 108]