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Nizam

Communication between Allen Bradley PLC and DCS

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I have 4 Allen Bradley PLCs which are 3 SLCs and 1 CLX This PLCs need to send data to Yokogawa Centum VP DCS. Instead of having and individual Modbus link to DCS, I'm planning to link all 4 PLCs by using Ethernet/IP and plan to buy 1 extra mini PLC which is Micrologix 1400 to become an interface PLC between the 4 PLCs and the DCS. Since the Micrologix 1400 has embedded with an Ethernet port (Ethernet/IP) and Rs485 port for Modbus RTU, the Micrologix 1400 interface PLC will communicate with DCS using Modbus RTU Protocol. Meaning to say, the 4 PLCS will send data to the Yokogawa DCS via interface PLC. The Interface PLC will become translator to translate from Ethernet/IP language to Modbus RTU language. My question to Expert: 1. Is this setup can works? 2. How to send data inter-PLC by using Ethernet /ip ? Is it just need to grab the tagname or there is an address for that? 3.Is Micrologix is capable to communicate with 4 PLCs using Ethernet/IP? Or just only 1 PLC? See the attached photo. Thanks. -Nizam- Edited by Nizam

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The Interface PLC will consolidate and gather the data probably 50 real data 32 bits from each PLC and send to DCS.

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I have seen the MicroLogix 1400 used for this sort of thing before. Option 1 is to have the MicroLogix execute MSG instructions to read data from the ControlLogix controllers. You will need to configure the ControlLogix with the "Map PLC/SLC Data" feature so that the MicroLogix can access REAL[x] array tags. That feature is how the MicroLogix can access ControlLogix tags, because MicroLogix doesn't know "tagnames". Option 2 is to have the ControlLogix controllers execute MSG instructions to write data to the ControlLogix controllers. You don't need the Map PLC/SLC Data feature because the ControlLogix does understand MicroLogix data table addressing, but you will need to configure some sort of handshake or data loss detection because you won't have the /DN or /ER bits in the MicroLogix to indicate that communications is working correctly. The Red Lion DataStation Plus is also a great way to provide data bridging of this sort, with the added benefit of a Web-based visualization screen you can check on easily. Using a third party that's known for their expertise in protocol conversion is sometimes a very good way to keep from finger-pointing between vendors.

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This is very true. I've learned that there are three words you never, ever say while on the phone to Rockwell tech support if you want them to even so much as pretend to be interested in helping you: "third party device" The only other point I'd make here is to take into account the future usage this PLC might experience. While a micrologix is certainly capable, I've seen it happen before where all of a sudden everyone realises that they can now get data from here to there and before long your "gateway" is flooded with more traffic than it was designed to handle. If it's likely that this could happen here, it may be worth at least entertaining the idea of spending the extra cash upfront to put in a ControlLogix system that can cope with plenty of future expansion. If you've been budgeting on a MicroLogix, and there are any accountants involved, you're unlikely to have that luxury, but it's at least worth keeping in mind :) Edited by ASForrest

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Hi ken, How difficult to configure the ControlLogix with the "Map PLC/SLC Data"? Do i need to purchase additional software license in order to enable that function? I don't have a luxury budget to change to Control Logix. I only have budget for micrologix 1400 since this only used for the so called 'Gateway' between the 4 PLCs and DCS. How about Micrologix 1400 communication with SLC? It is possible to communicate using Ethernet/IP and to pull data from 3 SLC PLCs ?

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AsForest, There will be no upgrade or expansion on this Micrologix. It will be used only for interface/ gateway between 4 PLCs and DCS

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It is very easy to configure the Map PLC/SLC Data feature in RSLogix 5000. It is a standard part of the basic RSLogix 5000 software. From the main menu, select Logic, then Map PLC/SLC Messages. You will enter a File Number and a corresponding Tag Name. The Tag should be an array of INT[x] or REAL[x] array type. If you enter "8" as the File Number and "DataForGateway" as the Tag, then a request from the MicroLogix 1400 for "F8:10" will be replied to with the value of "DataForGateway[10]". The MicroLogix can communicate with (almost) any SLC-5/05 controller or any other MicroLogix 1100 or 1400 controller. If you have an SLC-5/03 or 5/04 controller, you will need a serial/Ethernet gateway like the 1761-Net-ENI or Digi One IAP. The (almost) is that the SLC-5/05 originally had support only for the old proprietary PLC-5 Ethernet protocol. Any SLC-5/05 built in the last ten years or so will have support for EtherNet/IP, and any old one can be firmware upgraded.

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Thanks Ken for the long explaination. This helps me a lot. I really appreciate it.

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Hi Nizam, Just a question or two out of curiousity here - in terms of Yokogawa, I've only had experience with one of their small DIN-rail mountable controllers; is the process of setting up the RTU interface on their DCS simple? Is there an add-on module that you had to obtain for that? I'm assuming the DCS will be the 'master' device.

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Hi Nizam,...you don't need to have a bridge( Micrologix 1400) as an interface to connect your EtherNet/IP to Yologawa DCS ( Modbus RTU). It is easire and cheaper to use just an adapter (EIP to Modbus RTU ). Such a gateway is very helpful for data-exchanging between the Modbus RTU network and the EtherNet/IP network. It reads the register data from the Modbus RTU Master (Yokogawa DCS) and publishes these data to the input register data of the EtherNet/IP scanner. You only need to consider Maximum EtherNet/IP Input/Output data size of such an adapter. I can refer you to GW-7473 which has : 200 bytes data size: http://www.icpdas-usa.com/gw_7473.html?r=mohsen Or GW-7473 which has 500 bytes: http://www.icpdas-usa.com/gw_7472.html?r=mohsen Good Luck

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