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Modbus RTU

I'm going to connect a few MSA gas detectors to DeltaV M series via Modbus RTU. However I used Modbus with other PLCs and DCSs, it will be my first experience with Modbus communicating in DeltaV. Could you please define a procedure or introduce source and documents, I can use?

bardia61

• 20 Apr 2017 5:32 PM
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12 Replies

• fairchdm

  

  • 21 Apr 2017 3:10 PM

  Not sure of your DeltaV Rev and what Modbus protocol you are using (e.g. RTU, IP). If you are using serial I would start with KBA: AUS1-198-990302090554.
  You will also need your gas detectors Modbus Map.

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• dave_marshall

  

  • 21 Apr 2017 3:26 PM

  Hello,
  
  There are several ways to get MODBUS data into DeltaV.
  1. VIM
  2. OPC
  3. EIOC
  
  For a small to moderate number of gas detectors, the VIM is probably the easiest way to get the data. VIMs (Virtual I/O Module) are produced by a company called Mynah in the US. I'm not sure if you can purchase them through Emerson or not, but they can point you in the right direction.

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• Alfred Pol

  

  • 21 Apr 2017 3:49 PM

  In reply to fairchdm:

  VIM cards are manufactured by Emerson nowadays. Only thing is that the Modbus TCP/IP driver for the VIM card is developed and delivered by Mynah. In Europe the driver can be obtained through Emerson (I am not sure about other regions).
  
  Are you using serial Modbus or Modbus over TCP/IP? For the first you should use the DeltaV Serial Card.

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• Alan K

  

  • 21 Apr 2017 4:06 PM

  In reply to dave_marshall:

  A VIM (with the Modbus driver) can talk both Modbus RTU (serial connections) and Modbus TCP/IP (network). The VIM can handle approximately 4 times the number of remote devices and/or data flow as a DeltaV serial card. But it costs significantly more than the DeltaV serial, and requires 4 slots in your DeltaV controller (must be either card slots 57-60 or 61-64).
  
  For smaller applications (1-6 remote Modbus devices), the DeltaV serial card is more cost effective and only takes up 1 card slot (any open slot). It does Modbus RTU (serial connections) out of the box, and can easily do Modbus TCP/IP (network) when combined with a Modbus protocol converter such as the MESR901 from B&B/Advantech (or numerous other similar products). I use the DeltaV serial card with the protocol converters, and have been very pleased with the results.

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• bardia61

  

  • 21 Apr 2017 4:39 PM

  In reply to Alan K:

  The devices are RTU. Currently we have installed VIM gor connecting an Allen-Bradley PLC to DCS, 2 ports are still free. can you explain how I can use VIM as RTU? I thought it is for TCP. You mean I add a converter?

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• fairchdm

  

  • 21 Apr 2017 5:17 PM

  In reply to bardia61:

  Have you read the "Books online" article for setting up the VIM for serial? Some differences may be present depending on your version of DV and controller type.

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• Steve Linehan

  

  • 23 Apr 2017 3:23 PM

  In reply to Alan K:

  Alan
  
  On a quick clarification. Are you saying that a single VIM Card (Or redundant pair) can handle multiple protocols simustainously. Thats a new one for me. I you can confirm that this is possible I would appreciate it.
  I would be careful stating it can handle Modbus RTU serial. I know it can do Modbus RTU over TCPIP but is that not a seperate protocol to Modbus RTU Serial which has a different hardware layer.
  If you can confirm that a VIM card can connect to a device that has a Modbus RTU serial hardware layer and is expecting XON/XOFF and DTR, CTS RTS etc it would be great.

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• Alan K

  

  • 23 Apr 2017 9:22 PM

  In reply to Steve Linehan:

  I talked with Mynah tech support 2 weeks ago about this exact issue. We are considering using a VIM to communicate with some vibration monitoring equipment via Modbus TCPIP. Since this project will only use a portion of the capability of the VIM, I wanted to know if I could also run cable to the same VIM for Modbus RTU (RS-485) to other Modbus devices. Assuming that they understood my question, and gave the correct answer, Mynah stated that is possible. But to be clear, I have not actually done it yet. Project completion is currently set for September.

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• Tyler Anderson

  

  • 24 Apr 2017 12:38 AM

  In reply to Alan K:

  They misunderstood your question.
  
  The VIM is capable of TCP/IP connections only. There is no way to hook up RS485 directly to a VIM. If you need RS485, you'd need a serial to Ethernet converter to get that data into the VIM (Or directly into a real serial Card.)

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• leirbag

  

  • 24 Apr 2017 8:46 AM

  www2.emersonprocess.com/.../DV_PDS_M-series_SerialInt_Series2.pdf

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• Jake Nichelson

  

  • 24 Apr 2017 12:15 PM

  Hopefully I can summarize this issue and clarify some of the points that have been made about the VIMs' capabilities in this thread.
  
  1. The VIM only has an Ethernet port; therefore, it only supports Industrial Ethernet protocols directly (like Modbus TCP/IP). A Modbus TCP/RTU gateway can be used to allow the Modbus TCP/IP VIM to communicate to Modbus RTU devices.
  
  2. The VIMs support Modbus TCP/IP, EtherNet/IP, and PROFINET Industrial Ethernet protocols. A VIM can only support one protocol. A single VIM cannot simultaneously communicate via Modbus TCP/IP and EtherNet/IP for instance. At best you can have two VIMs connected to a single controller where each VIM uses a different protocol.
  
  If you are looking to integrate a set of Modbus RTU devices to DeltaV then you have several options:
  
  Option 1.a: DeltaV Serial Card with Standard Firmware - The DeltaV Serial Card is shipped with Modbus RTU firmware.
  
  Option 1.b: DeltaV Serial Card with Enhanced Modbus RTU firmware - This firmware is developed by MYNAH Technologies. This firmware will allow you to integrate devices that use extended Modbus Addresses (40,000/400,000 for Holding Register ranges for instance).
  
  Option 2: DeltaV Virtual IO Module 2 (VIM2) flashed with Modbus TCP/IP firmware (IOD-4111) in combination with a Modbus RTU/TCP gateway.
  --
  
  Now, putting all of that aside, you mentioned that you are integrating Allen Bradley PLCs. Using Modbus to integrate Allen Bradley PLCs is possible but it is not the most common approach. Without knowing anything about your configuration, I would recommend using a VIM2 with EtherNet/IP firmware to integrate Allen Bradley PLCs rather than using Modbus RTU or Modbus TCP/IP. All Allen Bradley PLCs support EtherNet/IP if there is an Ethernet port. If you are using an older PLC that does not have an Ethernet interface (such as some models of the SLC and Micrologix), then you can use the 1761-NET-ENI to add an Ethernet port. If you are using a more modern PLC (CompactLogix or a ControlLogix for instance) then the most logical integration path is definitely to use EtherNet/IP.
  
  If you have any further questions about the VIMs, feel free to open a support ticket at MYNAH.com. We can help you with pre-sales questions without a support contract.

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• Steve Linehan

  

  • 25 Apr 2017 7:49 AM

  In reply to Jake Nichelson:

  Jake
  
  Thanks for the clarification. My current project has 1 VIM Pair for Siemen's. (Modbus over TCPIP, Yes I would have preferred to use PROFINET but that decision was already made before I joined the project.). 1 Vim Pair for Allan Bradley (EtherNet/IP). Two Serial Cards running RS-485 Modbus RTU. We have other communication protocols for small equipment around the plant (RS-232 Modbus RTU for example) and use protocol converters to convert these to Modbus over TCPIP.
  
  Just wanted to clarify that we needed the multiple VIM's and Serial cards to do this. We could have done it with many converters but this was a good comprimise with three main protocols and all others being converted to one of these three standards.

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