Ethernet vs Profibus vs Devicenet 1

[jsearl]

Hello Guys and Gals

I have been tasked with coming up with a recommendation for which form of communication network to go for in a water process control environment. This would include PLCs' conneted to devices having 4-20mA I/O and digital I/O and conceivably intelligent MCCs' over a site wide distance of say upto 2000 metres. Would anybody be good enough to give me a start at how I can go about collating the necessary information to make this recommendation?

Thanks very much.

John

 

[VEBill]

One option might be SCADA (Supervisory Control & Data Acquisition), but I doubt it's the optimum choice. Mentioned for completeness.

 

[jsearl]

Thanks VE1BLL.

Its more the selection of the network architecture hardware I was trying to get a handle on.

 

[jraef]

Where you are might make a difference. For example if you are in Germany, Profibus makes sense being that most IEC MCC mfrs must contend with Siemens being dominant there, much of the rest of the EU as well, therefor IEC MCC mfrs must offer Profinet options to be able to compete. But if you are here in North America, nobody besides Siemens has adopted Profibus as a standard network. Most can adapt to it if necessary, but it is not the preferred network for anyone except Siemens.

DeviceNet is an aging standard that may have outlived it's usefulness for new greenfield opportunities, but if you ALREADY have it installed and have standardized on it (which means overcoming the learning curve challenges it presented), then there is no real compelling reason to change. But I would no longer implement a ground up new DeviceNet installation, especially with any appreciable distances involved.

The coming wave is EtherNet, read "The Internet of Things" papers that Cisco is putting out. Most MCC mfrs in North America are offering EtherNet intelligent MCC options, some better than others, but it's adaptation is more desired than adaptive because it offers some distinct advantages over DeviceNet, chiefly being able to reprogram things like VFDs and Soft Starters over the network, possibly even automatically when units are changed out for repair and rlacement units are programmed differently or not at all, because the programming can be stored outside of the unit and pushed down to it if there is a mismatch recognized by the system. All the new restrictions on Arc Flash protection are making that more and more important, because there is no better way to protect electricians that to keep them from having to open doors to check or change things. The protocols used, EtherNet/IP, Modbus TCP, or even ProfiNet, will vary from one mfr to another and that's a different discussion, but the hardware and media is the same, which makes it easier to implement.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[jsearl]

Thankyou Jraef for your reply.

 

[mikekilroy]

Its more the selection of the network architecture hardware I was trying to get a handle on.

First, get a handle on difference between HARDWARE and software. Your comment above is wrong. The hardware for all three listed are IDENTICAL. They all use RS422 or RS285 depending how you define multidrop. Their differences are SOFTWARE protocol.

Past that, figure what PLC hardware you are and in future will be using. That should help you decide which software archatecture to lean toward. for instance, Jraef will not promote his company, but AB, aka Reliance, etc., now uses ethernet/IP protocol - again same hardware.

Then there are other RS422 protocols like canbus, sercos II, and lots of proprietary SOFTWARE protocols over same RS422.

What ethernet, ethernet/IP, profibus, sercos II have in common is they like to send POSITION DATA back and forth. Knowing that current loops run at 2-3khz, velocity loops at 50-200hz, and position loops at 1-30hz, you can see that position loop data data is SLOW and thus can be sent over packets at these slow(?) 100mhz rates..... The proprietary methods like Delta Tau's Macro ring, MEI's special, etc., are there because of need to send either the faster velocity or current loop data.

So know what you want to accomplish. If it is to turn on/off i/o stuff and maybe go so far as to tell a drive where to go (position loop data), then any of the high level slow stuff is fine.

Then know what YOUR hardware is: if AB PLC stuff, stick with ethernet/IP assuming you dont need really fast communications.

http://www.KilroyWasHere<dot>com

 

[mikekilroy]

I meant to add you should google/study the word 'deterministic' in regard to communications. That will help you identify if you eed it or not. FAST is usually deterministic; slow like ethernet is not. Good use out there for both methods depending on the need.

http://www.KilroyWasHere<dot>com

 

[LionelHutz]

The hardware has to support the communications protocol you select so you may want to start with a list of the protocols that the hardware supports. No point picking Ethernet if a bunch of the devices only support RS-485 or a version of CAN bus as an example.

 

[mikekilroy]

LionelHutz thank you for clearly stating what I tried to and messed up:

First, get a handle on difference between HARDWARE and software. Your comment above is wrong. The hardware for all three listed are IDENTICAL. They all use RS422 or RS285 depending how you define multidrop. Their differences are SOFTWARE protocol.

I meant all those you listed use the same ETHERNET hardware, not serial RS422/485. Then there are all those serial RS422/485 hardware based types also.

http://www.KilroyWasHere<dot>com

 

[jsearl]

Thanks Guys. I appreciate your inputs.

 

[mikekilroy]

Ignore my obviously can't get right posts about which hardware base your listed ones are on. My mind and fingers are definitely not on the same page! I will try once more to get it right:

ethernet hardware base: ethernet, ethernet/IP, etherCat, CANopen, profinet, sercos II, etc
serial rs422/485 base: RS422/485, Devicenet, Canbus, MEI Synqnet, etc
Optical cable: Sercos

I THINK this is correct, but check yourself to be sure. The future does seem to be going ethernet hardware base so probablyi the hardware platform you want to go with. Then pick the software protocol...

http://www.KilroyWasHere<dot>com

 

[CarlHenning]

If you choose PROFIBUS, it does not matter what continent you are on nor what PLC or DCS supplier you pick – PROFIBUS will be supported by a certified competence center in the area and the supplier can connect PROFIBUS. (Yes, even Rockwell.) The organization that created, maintains, and educates about PROFIBUS and PROFINET is PI (PROFIBUS and PROFINET International). PI has certified over 50 PI Competence Centers; see the full list at [URL unfurl="true"]http://www.profibus.com/pi-organization/institutions-support/competence-centers/[/url]

My only other advice would be to favor PROFINET over PROFIBUS as the backbone for your project. As an Industrial Ethernet, it will have a longer life. And improvements in commercial Ethernet will be leveraged.

In North America, PI North America (a non-profit trade organization) provides many educational opportunities from webinars to free training classes to fee-based, week-long certification classes. Visit us.profinet.com for a listing of classes, installation guides, and much more.

 

[jraef]

Maybe I should have made it more clear: I was addressing this portion of the original post.

... and conceivably intelligent MCCs' over a site wide distance of say up to 2000 metres.

Here in North America (again, don't know where you are), MCCs cannot be assembled willy-nilly with just anything you like inside, there are standards, testing and approvals that must be adhered to. Only Siemens uses Profibus here in North America as a standard "intelligent MCC" internal communication bus, all others use either DeviceNet or Ethernet (in one form or another). Even Siemens cannot provide you with a Profinet wired MCC, it will be Profibus, then a Profinet adapter somewhere for higher level connectivity, which is how anyone else would accomplish that as well. If you want a SINGLE communication system here, it's DeviceNet or Ethernet, then since it is 2000m, I personally would not attempt to implement that with DeviceNet any longer since Ethernet is now readily available.

But outside of North America, I would likely choose Profibus inside of the MCC because chances are very high that the system will have to connect to something from Siemens or any number of other EU based suppliers who must contend with their dominance and follow suit.



"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[djs]

First off, the three communications systems listed, all use different hardware. Profinet is RS-485, DeviceNet is CAN (a Bosch standard developed for cars) and Ethernet uses several different (differential TBase, optical etc). If you are in North America and have no existing infrastructure, I recommend going to Ethernet. In Europe there is some merit going with Profibus. Ten years ago the situation was different and Profibus was the most accepted protocol.

 

[mikekilroy]

I am glad I am not the only one who writes what they don't really mean! I feel a tad exonerated!

Profinet is RS-485, DeviceNet is CAN

Wiki: PROFINET is a standard for industrial automation using a computer network. PROFINET uses standards such as TCP/IP and Ethernet.

And of course DeviceNet and Can are both RS485 based serial links.

http://www.KilroyWasHere<dot>com