SLC500 to Compactlogix Migration

[oldnerd 3]

I have searched AB knowledge base and can not find the answer to my question, maybe I forgotten how to read. I have a project to change 4- SLC 500's over to Compactlogix to get them off DH+ and onto enet, I will replace the processor in each of the 4 racks with a 1747-AENTR and leave the I/O and wiring intact. I have a total of 35 I/O modules in the 4 racks. I have been having difficulty coming up with just which CompactLogix Processor I need to use, on AB knowledge base I seem to be getting conflicting information. Which Compactlogix processor will handle 35 I/O modules ?

Any suggestion are welcome.

Thanks 

[pcmccartney1 141]

I might be wrong but....

The limitations on I/O Modules for the CompactLogix are with regards to the 1769 bus.  I think that because you are using an 1747-AENT, you would be more concerned with EtherNet connections and probably are fine.

I suggest you test configure say a 1769-L30ER and see how many 1747-AENTs you can add and have the controller verify.  You next consideration will be memory for code.

[PLCMentor.com 60]

There is another thing to take into account with this also.  Are the existing controllers on four separate independent machines?  If so then I would leave them on separate processors.  If they are controlling different parts of a combined line or machine then combining them makes sense.  The question you want to ask is, "Could I take this down and not affect the others?"  If so then keep it on a separate processor.  Maintenance, upgrades, etc will be made easier.  If taking down one processor requires all the others to be out of service anyway then combining makes sense.

[Joe E. 259]

To what PLCMentor said, even if they're all the same line, be careful combining them into one processor.  We had an engineer do that about 15-20 years ago.  He combined 3 PLC-2 machines into a single PLC-5 by converting 2 of the 1771 racks to RIO (remote IO).  Now, we're faced with a dilemma where we need to replace one of the machines with another one that's a completely different type.  Of course, the machine we're replacing is the one with the now-combined PLC-5 processor in it and we don't have very many PLC-5 CPUs laying around so we can't easily just replace the RIO modules with PLCs.  We're looking at a forced migration with very limited time to do it.  "They" also want the machine we're taking out to remain "intact" and able to be run in another facility so we can't just rob the CPU and re-address the RIO racks.

If there's ANY possibility that you might at some time in the future replace just one of the machines and not the others, seriously consider leaving each machine with its own PLC.

 

We had another machine that originally had a PLC-5 that "they" upgraded to a ControlLogix L55.  They replaced the PLC5 CPU with an RIO module, turning it into a remote chassis of the L55, which was in the same cabinet.  They didn't do a very good job of documenting everything, so when we tried to trace out stuff in the code to figure out which sensor/switch/whatever wasn't happy, it was VERY difficult.  If you turn these SLC 500 racks into remote racks of another PLC, whether it's one PLC for all of them or one PLC for each of them, DOCUMENT, DOCUMENT, DOCUMENT!  Make a detailed cross-reference so it's as easy as possible to correlate the tag in the PLC to the physical IO point.  Your electricians will thank you later...

[oldnerd 3]

All of you, thank you for the good advice, you brought up some points that I will need to give good consideration to. This is a continuous line, if one piece of equipment goes down the rest can not run because of interlock and it is in sections along the whole line. All of you I'm sure know how it is when you go to the upper management to procure funds for projects they come back and say cut the dollar amount and we will approve it, then again and again. However they have no problem with complaining about the current problems that you are trying to fix.

Keep it simple

Oldnerd