Modbus Communication

I am planning to use the MODBUS feature of Schenider. There are going to be 12 RIO panles with more than 1500 I/O on MODBUS communication (1000 Digital,500 Analog). These 12 may be at various distances, the maximum being around 50 metres away. The baud rate proposed by Schneider is 1.5 Mpbs.How long will it take the Emerson DCS system with (VE3006 MD+) processor to communicate with all 12 RIO's.I am not sure about the capabilities of Modbus communication.pls suggest

I think you will use Modbus Plus, not Modbus. Make sure your DCS has Modbus Plus communication

We have modbus+ (newer) interfaced to a Bailey Net90 DCS (old)
The communication uses a GPI (general purpose interface) and is quite slow. They have been talking about an upgrade.
The Modbus+ network is very fast a quite reliable.
It uses a token pass structure with maximum 64 nodes total length 1500' before using a repeater.
multiple modbus+ networks can be connected together and addressed through bridges.

Brian.

Modbus TCP/IP would be a better route to go.

Modbus RTU is slow and Modbus+ is getting a little out of date (the new Schneider M340 doesnt even support it).

Modicon users... chime in here

I am only familiar with Modbus Plus as a peer-to-peer protocol. The Quantum controllers I worked with (10 years ago) used it for HMI and controller-to-controller messaging and HMI links, and used the S908 remote I/O protocol to scan racks of Quantum I/O.

Can Modbus Plus also "scan" I/O racks ?

Modbus Plus runs on twisted pair wiring at 1 Mb/s. The S908 Remote I/O protocol runs on co-axial cable at 1.544 Mb/s. This is one of the reasons that I think that Sandeep is not using a Modbus or Modbus Plus network, but rather an existing Modicon 984 or Quantum controller I/O network.

Sandeep, you need to specify what kind of I/O modules and architecture you plan to use. Are these I/O modules already in place, or are you installing them new ?

As I understand it, part number VE3006 is an Emerson DeltaV controller module. Do you know the part number of the network interface module you are planning to use ?

What the ratio of discrete I/O to analog I/O? half and half?
Are you planning on reading indiviual coils or packed words?

IS Modbus TCP or Modbus over serial?

Is this Modbus through an Emerson Modbus master or with an OPC server acting as a proxy Modbus master?

Ken Roach said:

Can Modbus Plus also "scan" I/O racks ?

Click to expand...

Modbus PLus can be used to automatically "scan" blocks of I/O (i.e. Momentum and Advantys) using its built in global and specific read/write functions. These read/write commands are passed along with the token so no additional user programming is required. However I believe this automatic function is limited to 64 4x words after which you would go back to using standard communications. Modbus TCP I/O scanner does not have this word limitation.

Depends if its DIO or RIO.

DIO sits on the MB+ network and has its own MB+ node address etc. RIO works from a RIO scanner card and is programmed differently.

I think we need some more detailed information as everyones guessing here.