Configuration question

[Mendon Systems 22]

It has been a while since I configured an A-B system (PLC5 days) so rather than try to learn all the new stuff I would like some expert opinions. I have an application which requires about 50 remote sites to be linked back to a PLC over an Ethernet connection. The link they want to use is fiber Ethernet because the sites are miles apart. Each site will require at least two analog inputs and one digital input. Some require more inputs and a few need some digital outputs also. All of this gets collected up by one PLC and handed off to an existing Intellution SCADA system. Just browsing the A-B catalogs it looks like a Compact Logix L23 CPU with Flex I/O over Ethernet adapters would be the appropriate setup. Comments will be appreciated.

[BobLfoot 301]

THe Logix Families are critical when it comes to connection counts. There is a connection count limit for the cpu and a connection count limit for each ethernet adapter on your chassis. I'm not familiar with the exact numbers but the RA site has a nice page lsiting connection max's and nominals. STAY BELOW THE NOMINALS. Now looking at one remote site your two analogs and single digital would consume 3 connections to the cpu and possibly 4 if there were outputs present worst case, With a count of connections in 125 - 200 range {Kentucy windage -- I didn't run the numbers} I'd lean toward a full bore ControlLogix L6x processor. For the record I did a job one time with 120 ethernet HMI's which had two pushbuttons and two lamps on each HMI that was it. The HMI's were ethernet back to a ControlLogix Rack. We wound up putting Three L5x CPUs and Seven ENET Cards to get decent propagation delay times. OK The rest of you gurus, That means you Ken Roach, prove me wrong. :)

[Ken Roach 194]

I always argue with success, don't I ? I absolutely agree that the Connection count is the elephant in the room: even though it's a small number of Analog channels, the underlying controller resources to connect to them are much less in the CompactLogix family than in the ControlLogix family. I gotta get some rack time tonight, but I'll point you two places: 1. POINT I/O. Best stuff for granular, low-point count applications. 2. CompactLogix next-generation controllers. The new hardware gives them enough Ethernet performance to say "CIP Connections limited only by controller RAM". I would add "and Ethernet daughtercard packets/second" but as a practical matter you will run out of RAM before running out of CIP connections. Ask your local RA salesman about the new CompactLogix controllers and have a talk about their ship dates. http://literature.rockwellautomation.com/idc/groups/literature/documents/pp/1769-pp010_-en-e.pdf A full-blown 1756-L71 and 1756-EN2T would put to rest any memory, resource, or availability concerns, if you can afford it. I usually say "if you're only building one, make it a ControlLogix".

[Michael Lloyd 85]

Connection count aside (it's been covered. I typically have (2) ENBT's in my panels. One for the connection to SCADA and one to a remote IO rack if there is one. Remote IO lives on a different subnet <10 dot> just to keep "trash" off of my remote IO comm card) I agree with the others. Processing power is your friend. I would up the processor to the full bore L61. It's not a lot more expensive in the long haul I did a little job a few years ago that used MDS iNet radios and point IO to turn water wells off and on for a natural gas storage site. They were leaching out a cavern in a salt dome and the fresh water came from wells that were about a mile away. I really like point IO. It's easy to set up, has a small footprint, and "lives" on the processor as if it were local to the processor (unless the radio link goes down. That's always a fun thing to deal with but in this case the water well tripped off on over pressure so if comm went down the main plc started slowly closing the incoming valve. You don't want to close a fluid line quickly. Water hammer is an amazing thing) Having a fiber connection to the remote sites should make it easy to install point IO racks. The ONLY caveat that I can think of in the short time I've thought about this is that if the link goes down point IO is not "intelligent" other than the link fail mode that you can set for each type of card. If the remote site needs something to happen if the comm link goes down then the remote site will need a processor. In my example above the customer didn't require "intelligence" at the remote site.

[Mendon Systems 22]

Thanks guys! I sort of thought it wasn't going to be that simple. Nothing with A-B ever is. I found one page in the catalogs that lists some connection limits but I'm not sure if it is the one Bob was referring to.

[andybr 5]

Have you considered using a MicroLogix (1400?) at each remote site rather than the Flex. This needs less connections and allows you to have "Local" control in the event of comms failures.

[Mendon Systems 22]

I looked at the Micrologix first, but according to the catalog the Ethernet interface is only rated for temperatures above 0 degrees C. I need at least -20 degrees C. Edited 3 Jan 2012 by Mendon Systems