Device net

Hi,



I am a noob so I apologize if these are kind of silly questions. I am working for a company that has to provide controls ethanol refinery. A third party is setting up DeltaV and the details behind the process and our company is setting up all the instrumentation required. I just want to lay this out as I understand it so if anyone sees anything that is incorrect I can be corrected.



DeltaV is going to interact with the AB PLC uing DeviceNet. DeviceNet is a protocol and system for fieldbus communication and is digital opposed to older 4-20 mA analog systems.



To get your PLC, to communicate with a DeviceNet system you need



1. compatible PLC and a scanner card for that PLC

2. DeltaV or some other compatible DCS system

3. Cables and DeviceNet nodes





Questions I have with the capabilities with the system is





1. I have read on bulletin boards that DeviceNet is flaky with allen-bradley systems? Is this true or is this largely due to improper implementation?



2. What information about the instrumentation can be gathered by DeltaV other than measurement data? Can On and Off state information be relayed? What other information can be relayed to DeltaV?



3. How reliable in general is DeviceNet?



I don’t have any experience and am just in the beginning of my looksie in this area so forgive me if some of these are ‘duh’ questions. Any links to good forums or sites would be appreciated, too.





Doug

[email protected]

Only instances where I have seen D-NET being flakey is due to one bad connector somewhere on the trunk. Because D-NET requires terminating resistors at either end of the trunk the whole network can be brought down because of the flaky connection.

Best not to use D-NET in harsh environments, such as high temperature , high humidty, with high vibrations. We do work in a plant with the above conditions, and another company installed a series of D-NET controlled 'Think-Top' mixproof valves, and the other company has all kinds of grief due to above mentioned conditions.

D-NET works great in MCCs

Ian

It was "flakey" for us when we used it with Modicon. I would be leary using it with another controller other than AB again. I haven't used it with DeltaV but personally I wont try it as a third party again.

1. I have read on bulletin boards that DeviceNet is flaky with allen-bradley systems? Is this true or is this largely due to improper implementation?

Click to expand...

This is what I ould put it down to. Lots of people have had problems, but almost all of them come down to the copper at the end of the day.

I haven't used it with DeltaV but personally I wont try it as a third party again.

Click to expand...

We use it wit Omron for remote IO, and have no issues at all. There is a lot of DNET products out there, some better than others I guess.

To a certain extent, you could liken it to modbus, this was a modicon product, but there is a lot of modbus compatible products, and they all work well.


My 10c anyway.

If you don't have moving machinery, people, forktrucks... near to the devicenet cabling, it's probably ok. Otherwise, prepare to have many people saying bad things about your ancestry.

Just to clarify I have used device net with ab over the years and I feel that when used for applications that it was designed for it works as should.

When we used it with modicon nodes would intermittently be lost sometimes requiring us to power cycle the network and the remote i/o if faulted or disconnected would retain its last value which was problematic to us.
We did insure the integrity of our power and cabling via network analyzer.

Like I said it's just my opinion that I will not put myself in that situation again.

My experience with Emerson DeltaV's DeviceNet interface goes back to their first installations, but I have not worked with an installation in the past two years.

DeviceNet works best, in my experience, with Rockwell and Omron controllers. 90% of DeviceNet problems come from shoddy installation, so read the installation manuals and follow their recommendations.

Ask Emerson or their integrator to furnish a document showing that their network interface is ODVA Compliant.

I agree fully with Ken - Device Net certainly works best with Omron and AB products.

If you follow the "RULES" you will be OK. Cut corners and you are in trouble.

I would also suggest that if you wish to use Device Net products, go to www.odva.org and check out if the proposed equipment has been tested by ODVA for compliance. This, unfortunately, will only prove the hardware and not flaky EDS files. I have had a few and have had to fix them - ABB in particular.

I have used DN with AB, Omron, Pepperl + Fuchs, ABB and several other products. The only one that caused me any real problems was ABB with a flaky EDS file.

I have now installed perhaps 30 - 40 DN networks and have never had to go back to them. 1 network even includes fire retardent thick DN cable that we had manufactured for a job. It was quite expensive but runs the full height of a 50 story building without any problems. A lot cheaper and easier than having to run the cable in steel conduit for sure.

I might add that one network I have running includes an Omron PLC, AB powermonitor, Omron I/O blocks and 3 x Pepperl + Fuchs absolute encoders in a crane on top of the Sydney Harbour Bridge in all kinds of weather/temperatures from very hot and humid to icy (frost). DN has not failed even in these conditions.

i have been using d-net with modicon for 2 years & have had zero problems , it all comes down to installation.

I used DeviceNet in a Sawmill for years. This is probably one of the worst environments for vibration with the big logs dropping into conveyors and such. All of my MCC's were Intellicenters and the Freq Drives were Mitsubishi with DNET cards. The only problem I ran into was having a node in the mapping that did not exist. For some reason it would sporatically fault the CN2DN, but only one one of the Intellicenters. I had spares mapped in other MCC's and had no issues. Only map devices present and you should have no problems.