Choosing a Device Network

J

Thread Starter

Jonathan Mann

I am in the beginning of upgrading an out-dated DCS system with a new one. This system will incorporate "Smart Devices", and I am in the process of selecting a fieldbus network. I have noticed that Foundation Fieldbus has more instruments registered with it, but I can not find any thing with relation to Power Monitoring or with VFD's. Would it make more sense to use a network like DeviceNet up to the Controller Level, and use Foundation Fieldbus for my instruments, or to use the same fieldbus network-wide.

Any Suggestions?

Does anyone know any current Plant-Wide fieldbus installations in the US?

Thanks
 
Jonathan, too bad you cannot wait for my book now being published by ISA: Automation Network Selection. It covers this issue.

Your observation is correct; there are no VFDs with Foundation Fieldbus interfaces. Power monitoring is normally a function of the VFD for the motor it controls. There are no electric power meters of which I am aware with Foundation Fieldbus interfaces. You may search for Foundation Fieldbus Registered devices at this URL: http://www.fieldbus.org/ProductsAndServices/RegisteredProducts/

You may find that another fieldbus will be necessary to interface with these devices. Which one mostly depends upon who makes the VFD and power instrumentation. Siemens or ABB/Profibus, Rockwell/EtherNet/IP or DeviceNet, Schneider or Square-D/Modbus/TCP, etc. You may find that the availability of "smart" VFDs is very limited. Do not ignore LonWorks as a fieldbus for VFDs and electric power metering devices.

Until there is substantial demand, VFD and power meter suppliers will continue to avoid most fieldbuses.

Dick Caro
============================================
Richard H. Caro, CEO
CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +1.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected]
Web: http://www.CMC.us
============================================
 
V

Verhappen, Ian

The selection of the bus is a function of the device composition in your plant. This means the ratio of discrete devices, analog devices and "multivariable" devices such as motors and drives. The Fieldbus Foundation has a project underway to use their Flexible Function Block as a 'container' to transmit all the information from a VFD or motor drive to the Host controller via H1. Depending on the timing of your project, this will make it possible to do everything with Foundation Fieldbus. If you are already 'underway' your proposal of a network like DeviceNet for the motor information and H1 for everything else is a good one.

Don't forget that with FF you will likely also be able to get multiple Process Variable readings from a single installed instrument.

There are many plant wide FF installations in the US, including facilities by BP, Shell, and Smith-Glaxo to name a few.

If you contact me directly off list with your e-mail address I will be able to help you further with a bit more information.

Ian Verhappen
[email protected]
 
D

Donald Pittendrigh

Yaskawa - Profibus and modbus
Siemens Siprotec - Profibus (power quality and control)
Siemens Simeas - Profibus (power quality)

Donald P
 
J
Don't mix busses if you can avoid. Plenty of suppliers (including us, SMAR) can provide you with a system having interfaces to many different buses. It will work. But it will be difficult to maintain, as you need to learn many technologies. Go with Foundation Fieldbus (FF) and use conventional I/O for those devices that do not have 4-20 mA. Other buses don't really have anything equivalent to the FF Device Description (DD) and therefore hosts cannot provide an effective interface to devices using other bus technologies.

Jonas Berge SMAR
==================
[email protected]
www.smar.com
 
Jonas,

I never thought I would rise to the defense of Profibus, but fair is fair. Profibus-PA does include device descriptions called GSD, an acronym for a very long German word meaning device master data. For AI and AO devices, the GSD defines almost the same data as a Foundation DD. There are no control devices for Profibus, so there is no equivalent of the DD for PID. Siemens supports discrete field devices with GSDs in their PLCs.

There is a harmonization effort to develop an XML-based device description shared among PROFInet, Foundation, DeviceNet, and HART. Hopefully, this will become a standard included in IEC 61804, Function Blocks (FB) for Process Control, sometime next year.

DeviceNet and EtherNet/IP include a great deal of functionality in their EDS, which are Electronic Device Specifications, mostly aimed at discrete I/O. At least Rockwell supports ESD devices for their PLCs.

Dick Caro
 
S

Steven Landau

On September 27, 2003, Jonas Berge wrote:
> Don't mix busses if you can avoid....

We find that we use FF for analog instruments an Profibus DP for VFD's and Profibus DP Remote I/O for instruments not available in FF.

Also an AS-I network for On/Off Valves and misc DI/DO points is quick and easy in a non XP environment. This is expecially good for process development sites where things are always changing.

S. Landau
www.spec-eng.com
 
Thank you all who replied to my comment. I will consider all of your remarks. And maybe see some of you at the ISA convention in Houston.

Thank you again.
 
J
My message was not completely clear. Here's the long version...

The GSD file is not at all like a DD file. To some extent it is like the FF Capabilities file. The GSD file contains some identification information, but primarily the communication speed and the cyclic variables. Host interoperability is achieved by other means.

Profibus-PA has a physical (resource) block, transducer block, and input/output function blocks just like FF. These contain just as many parameters as the FF blocks. However, the acyclic parameters are not described in the GSD file. Profibus does have an equivalent to DD called EDDL (this is the one going into the harmonization project you mentioned). Profibus also have other concept for host interoperability: Profile and FDT/DTM. All three have relative merits and different supporters.

The concern that I have which I wanted to highlight to users is that no host, in spite of often sweeping claims, have good support for both FOUNDATION Fieldbus and Profibus and the others. If you look at Siemens they have a fantastic tool based on EDDL, but their system has no FOUNDATION Fieldbus. If you look at SMAR, Emerson, Yokogawa etc. we all have tools that support the FF DD, but there is no support for EDDL or DTM. I guess we all can connect Profibus devices and get the data on the screen, but without support for EDDL, Profile, or DTM you don't get full and easy support, with complete freedom of choice. Usually special screens have been created for some devices. Do you see my point? Depending on which "camp" you choose one bus is plug and play, the other one isn't.

In my view GSD provides connectivity but not plug and play interoperability like DD/EDDL. Using GSD the tool has the information to connect things together but not the data you need to put sophisticated device specific diagnostics on the screen or to present advanced parameterization options. You really need EDDL/DTM in the host to make Profibus easy to use. If you do, it is easy. If you don't, it becomes like Modbus.

Part of the problem is that in addition to the GSD there are three technologies to choose from. Today different tools use different schemes: EDDL (Siemens), Profile (E+H), or DTM (ABB, E+H, PactWare, etc.). And not all devices support all schemes. At SMAR we make Profibus-PA devices that match the standard Profiles, and we provide the EDDL files. Now we are working on the DTMs for the devices. No host today supports both EDDL and DTM as far as I know. Hopefully the DD cooperation project will result in greater support EDDL by Profibus devices and in many hosts. Hopefully we will see hosts that support DD/EDDL for both Profibus and Fieldbus in the near future. Until then I think it is better to stick with one network.

Profibus-PA and FF-H1 use the same wiring so not much extra to learn. But DeviceNet, ControlNet, AS-I, and Modbus/Profibus-DP use other media so there are many different things to learn if you mix too many of them. It is easy to setup, but troublesome to maintain in the long run.

Check out my book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" (buy online in hardcopy or download immediately in softcopy). If your email does not support this hyperlink feature correctly, please copy the URL and paste it into your Internet browser. Mind the line wrap, make sure to get the complete path all the way to the 3036: http://www.isa.org/Template.cfm?Section=Shop_ISA&Template=/Ecommerce/Product Display.cfm&ProductID=3036

I think the EDS is very similar to the GSD, but not an equivalent to DD/EDDL

There is more to network support than plopping in a card in the PLC. I think the configuration tool is most important.

Jonas Berge SMAR
==================
[email protected]
www.smar.com
 
Jonas, thanks for making this point clearly. Your message is that the fieldbus wars are continuing -- but no longer in standards committees. None of the leadership companies is making a move to back a single solution, any more than they backed a single fieldbus protocol. I gave up on IEC standards as the way to satisfy end user needs for a single standard -- the well-funded opposition was too great. It continues.

Just to see what can be done with EDS for discrete devices, you can search for the few DeviceNet enabled limit switches from Allen-Bradley and Cutler-Hammer (now named Eaton Electrical.) A very complete set of functions, not defined in a text file, is also implemented in some very expensive SDS limit switches from Honeywell Micro Switch. They do contact bounce filtering, pulse width detection, and pulse counting at the switch itself. Similar functionality is available with LonWorks devices and an EDS-like capability registered with the LonMark Association.

I had hoped that OPC/DX and OPC/XML would help solve this "too many standards" problem, but the latest releases only provide some cool tools, but nothing to reach down to the smart device level. At least that's my impression.

Dick Caro
============================================
Richard H. Caro, CEO
CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +1.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected]
Web: http://www.CMC.us
============================================
 
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