RSlogix500 network programing.

First off, thanks to this community for being a great source of information to me for years. I have been an electrician for 15 years now, and this place has been an immense help when i have PLC troubles. Please bare with me as this might be long winded.

I have taken over all MRO for a bulk export facility(conveyor and dust collector systems mostly), which is a Frankenstein of 1968-2006 parts and technology. I have relay logic, (2)GE LM90, AB SLC 5/03 & (2)AB Micrologix 1200. I have been tasked with "updating" all the PLCs to current off-the-shelf availability, since I can no longer find any LM90 replacement parts.

Our program needs are very basic, And i have been able to troubleshoot and maintain the system for the last few years without issue. The one area I am having real trouble with is the networking. In 2006 I replaced part of the old GE LM90 with two of the Micrologix 1200, networked to the SLC5/03. All three use adapters to connect to a fiber optic Ethernet we installed. The Programer hired at the time used 4 [MSG] commands at each plc. 1 read and 1 write going to each of the other PLCs. with a timer setup so each one goes in sequence. WE only need to share a few digital inputs and outputs between the units, with only a single Analog output from one unit to a single other.

My only problem with this is the time delay between them. It currently takes 5 sec when the farthest conveyor has a shutdown, for the next one to stop. So every time there is an over flow of product on the tail of the conveyor.

If i am going to be Replacing the remaining (2)LM90 with 1200 (simplest and cheapest solution), I need to find a way to reduce that time delay. Most units are 200m away, with the farthest being 300m.


The AB class i took years ago just skimmed over networking, and im not sure what class or book i can get to help me better understand what i need to do. Any help or info would be great.


Thanks!

I would be using a ML1100 or ML1400, that way you do not need a serial to ethernet adapter, they come with built in ethernet, they also use the ML1200 I/O modules, online editing, limited built in analog.

Far superior machine to the ML1200 for probably the same or less cost.

Alan

As above, I would replace all your PLC's with types that have native Ethernet capabilities.

ML1100 should be fine to replace the ML1200's, and possibly ML1400's or CompactLogix to replace the GE's and SLC's.

Talk to your local AB distributor I imagine they would be more than happy to come out on-site and work through a plan with you.

You say you need to reduce the time delay. Search in the program for the MSG instructions. The programmer probably used one or more timers to sequence through the messages. Can you speed up the timers? Shorten the presets?

Thanks for the ML1100 recommendation, my AB distro was just talking about those, but he is really pushing for an upgrade to Compact logix controllers.

The time delay is my biggest concern. When i have the time to do the shutdown for testing, ill try shortening the presets. What i don't fully under stand is why i need to have the read/write on timers to begin with. Or why I need the write function at all. Couldnt i just have the PLC read the few bits it needs to see?

You need the timers there so that the MSG instructions don't spam the network.

If there is no time delay then depending on how it is programmed the MSG instructions could be triggering on every scan which may be <10mS.

It is possible for a PLC just to read MSG the bits it needs.. there is not a requirement for there to be a write MSG as well, although it is possible it has been put there to do sort of handshaking or heartbeat checking to make sure that the comm's between the two PLC's are working.