Can you recommend a PLC capable of communication with up to 100 other PLCs?

I'm on the hunt for for a "Balance of Plant" PLC (or alternative) that is capable of exchanging (sending and receiving) a small number of bit packed status words with up to 100 "field" PLCs (20 to 100 dependent on the site implementation).

The field PLCs are Allen-Bradley Micro850s (so Ethernet/IP or Modbus TCP for communication protocols) and was considering using the same PLC model or product family for the "Balance of Plant" PLC however initial investigation indicates that it may not handle that many connections.

[LINK]Micro800 controllers: Connections capability
With firmware version 4 and higher the Ethernet connections capabilities are:
16 incoming
16 outgoing connections

Suggestions are greatly appreciated.

I'm not familiar with the Micro800 series. But we use a mix of Micrologix 1400 and Compactlogix for something similar to what you're doing.

We just make sure we stage our MSG instructions so that they execute sequentially. If a unit doesn't respond it goes onto a slow poll routine.

That method might work fine for you if you only need updates every couple of seconds.

You could look at a DeltaV PK controller. It is effectively a mini DeltaV DCS, with batch, continuous historian and all the other advantages of a DCS for balance of plant. It can easily handle the modbus TCP/ Ethernet IP requirements and OPC UA.

On side note, the list price is substantial. Also its only just released so has a few headaches to set up.

You could go with a Control Logix, the new ethernet cards support 128 connections. Another way which may be more scalable would be Control Logix with Prosoft Modbus cards, I think (don't remember for sure) each Prosoft Card supports 20 connections. The Prosoft cards do all the "work", so 1 CPU could host several Prosoft cards and consolidate the data.

I would second Ken Moore's Suggestion of a rockwell PLC. You could look at a CompactLogix, which have models that support up to 250 Ethernet/IP nodes. You could then scale down to 24 nodes according to site conditions.

See 1769-sg001 page 3 "Network nodes" Compactlogix 5380 / 5480.

tbennett4u said:

I'm on the hunt for for a "Balance of Plant" PLC (or alternative) that is capable of exchanging (sending and receiving) a small number of bit packed status words with up to 100 "field" PLCs (20 to 100 dependent on the site implementation).

The field PLCs are Allen-Bradley Micro850s (so Ethernet/IP or Modbus TCP for communication protocols) and was considering using the same PLC model or product family for the "Balance of Plant" PLC however initial investigation indicates that it may not handle that many connections.

[LINK]Micro800 controllers: Connections capability
With firmware version 4 and higher the Ethernet connections capabilities are:
16 incoming
16 outgoing connections

Suggestions are greatly appreciated.

Click to expand...

Our Underground area has a similar situation. We call the "Balance of Plant" PLC the "Data Concentrator". It polls data from all of the other PLCs, and presents a single interface to the HMI system and historian. It also handles all routing all of the various start/stop commands from the HMI to the correct PLC. I had a hand in the design when it was a bunch of Modicon PLCs being polled by a Quantum. They have since moved to almost all Rockwell.

The currently not-working-so-well system is a ControlLogix L61, but they ran out of connections on the 1756-EN2T. It freezes once in a while .. there are no connections left, they think .. and everything just backs up until the messages all time out. The PLC is still running but you can't connect to it with Studio - no connections left.

The Message instructions are being queued up and timing out, intermittent connections or PLCs just turned off when equipment was being maintained ... the communications was not tolerant of this stuff.

They did a short investigation into produced and consumed (not available on your Micros). It sounds like it just uses up too many connections. I hear that they have decided the message instructions is the way to go. But I know that there is overhead in managing how many are active ... our underground response time is targeting a 1 second update across about 50 PLCs ... and keeping track of the changes is going to be time consuming.

Since it is the center of the data communications universe, their plan is to add a second L61 in it's own rack, separate power supply, etc connected to a separate switch in a different location, with it's own ethernet card, doing the same job. It's not exactly redundant, but it sounds FactoryTalk View can use it as a 'second source' ? I hope I got that right.

Last I heard, the plan is 8 messages active at once, and the split is by area.

I hope they have a BUNCH of external documentation that explains their methods, what the design decisions were, and how to expand it later.

+1 Australian