Modbus Gateway (Replacing Slaves With PLC)

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If this has been asked and answered already, please point me in the right direction. I have a production line that uses Gefran Geflex temperature controllers on a Modbus and Machine Net communication system. The main control panel (MCP) is the master on the Modbus and communicates directly with 3 slave Geflex units (Group Leaders?) which then communicate with the others in that group via a Gefran Machine Net type interface (ribbon cable daisy chained from one unit to the next). The issue is twofold: These temperature controllers are slowly becoming harder to find AND they are a PITA to change out because they have to be put in place and then properly addressed using software on a laptop. This means more downtime waiting for someone who knows how to set these up to get there to do it say on a weekend/middle of the night type situation. (I do like my beauty sleep). I'm looking to replace these units with standard SSRs and control them with a PLC (P-2000 most likely). What I would need to be able to do is interface between the MCP and PLC in some way that the MCP still believes it is controlling 24 units (24 Modbus IDs) and have the PLC receive the reads and writes from the MCP and know which ID it was meant for in order to set the SV and respond with the PV and/or alarm codes as that ID. I hope that all makes sense. Basically I need a way for a PLC to act as if it were 24 separate Modbus slave units.

Could I just use a separate HMI next to the MCP? Yes, but there are temperature dependent routines in the main operation of the line (extruder run inhibit, etc.) that requires the information reported back on the Modbus. I've looked into Modbus Gateways but the MGs I've found so far don't seem to be capable of assuming the role of 24 different slaves and interfacing with the PLC in a way that would allow the individual control. 

Any ideas would be greatly appreciated.

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Yes, I believe that there is a gateway type product that might help you out.  It can take the inputs it gets from its from its slave side from the existing master and map these so that the master side writes as it needs to, to accomodate changes in the former slave architecture.  The slave side can pretend that a single port is mulitple fixed slave ID node addresses, on one single port. 

Try the email jschulze at iccdesigns dot com and ask him about the ETH-1000 (or whatever product) for your sitation.  He's the resident expert on control.com for Modbus situations like this and is product specialist at ICC Designs.  You can read a thread on PLCs.net where a somewhat similar situation existed.   http://www.plctalk.net/qanda/showthread.php?t=128109&highlight=intelligent+modbus+gateway


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