FieldBus or Network

Hi,

I was recently asked if Profibus is a fieldbus or network?? i had no answers. Can comeone explain difference between fieldbus and network. I heard from somewhere that Modbus Plus is a network but not Modbus. I am confused here. What about DH+??? Modbus TCP/IP???
can someone throw some light here.

Hello Jaichains;

we might just be splitting hairs here:

Fieldbus

From Wikipedia, the free encyclopedia


Jump to: navigation, search
A Fieldbus is an industrial network system for real-time distributed control.

A complex automated industrial system - say a manufacturing assembly line - usually needs an organized hierarchy of controller systems to function. In this hierarchy there is usually a central computer at the top, where an operator can monitor or program the whole system. This is typically linked to a middle layer of programmable logic controllers (PLC) via a bus system (e.g. Ethernet). At the bottom of the control chain is the fieldbus which links the PLCs to the components which actually do the work such as sensors, actuators, electric motors, console lights, switches and contactors.


I would agree with this definition, which is broad enough to cover most of the situations we face in our jobs: a fieldbus is one type of network, specialized for industrial control.

Hope this helps,
Daniel Chartier

Hi,


Sorry i meant is profibus a protocol or network actually.
is modbus protocol or network??

I think there is confusion over terms. Daniel presented a nice overview and explanation of a whole system above.

Fieldbus is a network, it is not the same as ethernet which is what I think you are probably referring to when you say network.

Fieldbus usually refers to field devices(pressure, flow transmitters, etc.) networked together. This is usually a slower more reliable type of networking then the usual office ethernet network. The hardware specs and everything are different.

You can then connect small fieldbus networks, using gateways, etc. over ethernet. The ethernet part is probably what you mean by a network.

Profibus exists on all those layers. There's Profinet, Profibus PA, etc. They all have their targeted application and use.

I'm not sure about Profibus, I've never looked into very deeply, but Modbus is a protocol. Modbus TCP is the modbus protocol using TCP, IP, and ethernet. Modbus RTU is a protocol over serial type networking, usually RS-485.

Profibus and Modbus are Protocols.

Modbus implements the Application layer of the protocol.

Profibus implements the user layer of the protocol. Profibus has versions which implement the Data Link and Physical Layers of the protocol, and one version (FMS) implements the Application layer.

You can use several transport or network layer protocols with Modbus or Profibus (like ethernet, tcp, devicenet, or fieldbus protocols).

When you use the term "network", you are probably thinking of the Transport and Network layers of a protocol, like TCP/IP, FTP/IP, IPX/SPX; DeviceNet and ControlNet define a network layer. RTU is a network layer for Modbus. Many automation manufacturers define their own network and transport layers for communication.

I think it might be theoretically possible to have Modbus over Profibus, but it would be really strange, hehe.


So to clarify: Network really means Topology...how the devices are connected together so they can talk. A network is part of an overall protocol, and a given network can support different higher level protocols.

$

Here is a link to a Fieldbus site with further links to many other sites. You may find this usefull.

http://ourworld.cs.com/rahulsebos/