Ethernet / Fieldbus / HART


Thread Starter


Difference between the Field bus / HART / Ethernet / Profibus technologies and which is suited for which applications...

Can any one suggest from their experiences?

James Ingraham

That's a bigger question than you might think.

Quick summary:

Fieldbus (or Foundation Fieldbus, which is what I assume you are talking about) is designed for the process industry. It is especially good at long distances and dealing with analog devices like valves and gauges. It has fairly impressive backing. More information is available at "": .

HART - Highway Addressable Remote Transducer. Foundation Fieldbus is generally designed as a replacement for HART. HART is an older standard that puts a communication signal on top of the ubiquitous 4-20mA signals used already by valves and gauges. More info at "": .

Profibus comes in three flavors, DP, FMS, and PA. The PA standard competes closely with Foundation Fieldbus in projects requiring intrinsically safe devices. DP is far and away the most common Profibus flavor, and is suitable for hooking up just about anything under then sun. Discrete I/O, analog devices, drives, everything.

It is ostensibly an open standard, but Siemens still has a fair amount of influence over what happens in the world of Profibus. The standard is much more widely used in Europe than in the U.S. More info is at (you guessed it!) "": .

Ethernet - Saying "Ethernet communications" is completely meaningless. There is nothing on the planet that you can hook up "Ethernet" and use it for control. You will be required to have some sort of protocol running on top of the Ethernet physical layer. The most commonly used is TCP/IP, but even that only gets you halfway there, because you need to know what is in the TCP/IP packet. Foundation Fieldbus has an Ethernet solution called HSE. The Profibus group has Profinet.

Allen-Bradley uses Ethernet/IP (where the IP stands for "industrial protocol" and has nothing to do with the IP in TCP/IP). Schneider/Modicon/ Telemechanique/Square D uses Modbus/TCP. There are numerous other Ethernet protocols used in industry.

If anything I am saying is news to you, you've got your work cut out for you. There is significant overlap in the uses of the networks you mentioned. I can't really say more without knowing more about your project. HOWEVER, I will say that despite that every vendor will tell you otherwise there is precious little difference in the real world amongst the various fieldbuses.

The Profibus guys will tell you that HART is useless and you shouldn't use it, but there are zillions of HART installations out there doing just fine.

Oh, and we haven't even talked about the other networks available, like DeviceNet, ControlNet, AS-i, Interbus-S, Lightbus, SERCOS, CANopen, WorldFIP, Seriplex, Sensoplex, SDS, LonWorks, CC-Link, CompoBus/S, etc. (Yes, I like listing. I just can't help myself.)

I daresay that your best bet is to talk to a vendor that you are used to dealing with and that you trust. Having support when implementing a network is more important than which network you pick.

-James Ingraham
Sage Automation, Inc.