Device net and Allen-Bradley PLC question

Information:
I do not have any exposure to device net, I always assumed that it was a type of RIO network. However, when discussing an upcoming project, device net was mentioned as a means of passing data between different brands of PLC's. Similar to Modbus.

Question:
Can this be done with Allen-Bradley PLC's? This will be for a small skid mounted piece of equipment, so I'm really asking about SLC's or Compactlogix. We're still buying new SLC systems, so that would be the preferred platform.



thanks,

Ken

AB was the prime developer for DeviceNet and yes it can do data. You can get more info on it and available products at: http://www.odva.org

Yes, it can be done. It's just not real easy in the SLC platform. I've only done this once so I'm not really an expert.

What you are referring to is explicit mesaging over DeviceNet. If I remember right this is the CIP protocol transfered in the non-cyclic data portion of a DeviceNet period. So as long as you set up your query right you can get information out of anything that supports this protocol.

You set up the messages in a specific area of the M-files that are assigned to the DeviceNet scanner. The meassage 'header' needs to contain information about who you are talking to and what you want. This is specific to the DeviceNet link and will be defined in the DeviceNet explicit messaging section in the DeviceNet manual. Depending on what you are talking to there may also be a secondary header that instructs the device you are talking to to do something, such as send you information. In my case I was talking to an Indramat PPC controller. So my data block had a DeviceNet header portion that told the DeviceNet components what I wanted to do followed by and Indramat PPC header that told the PPC what I wanted to do followed by the data. I think it is much easier if you stay inside the AB family as everthing you need is part of the CIP protocol and will be contained in the DeviceNet header. In my case I only needed to perform two or three different 'action' (such as 'read' or 'write') so I fixed the header information in a data block and the manipulated the data portion of the message as necessary. You also need to perform the acknowledge functions to keep the DeviceNet scanner happy. If you want to support a full blown explicit messaging system the coding will be relatively lengthy.

Now, CompactLogix is a little different story. The Logix family MSG instruction has a fill-in-the-blanks form for doing explicit messaging. You still need to know the appropriate attribute and instance information but the Logix MSG instruction takes care of all the handshaking stuff.

I hope this helps some.

Keith

If I understand you correctly, you want to exchange data between different brand of PLC and you want to use a AB PLC as a "bridge"?

Another possible solution I want to throw out there is to use a PC based solution utilizing OPC DX technology. If my understanding of OPC DX is correct; one can connect all the PLC to a PC using OPC server for each type of PLC then add a DX plug-in to exchange data between the OPC servers. Hopefully, someone who knows OPC better can enlighten us all on such an idea.

more details

My company is looking to purchase three thermal oxidizers for three different plants(my plant is one of the plants). None of the three have identical control systems. We have AB, TI & Foxboro DCS . Site two has AB, TI & Foxboro . Site 3 is all TI (older plant).

We are trying to get a common specification together, so that we can purchase all three units as a package, and perhaps get better pricing.

The goal at plants 1 & 2 is to connect the oxidizers to the DCS system. Plant 3 needs to connect to TI, or maybe just Wonderware.

Device net was mentioned as a means of communication (by plant 2), that would met the above requirements. I think modbus or profibus will be a better option, just wanted to check out the feasibility of the device net network before I put my foot in my face.

Harryting,
Since these are critical pieces of equipment, anything running Windows in not an option. (Not reliable enough)

Ken

Harryting,
Since these are critical pieces of equipment, anything running Windows in not an option. (Not reliable enough)

Click to expand...

YEAH!!!!

Modbus is slow but has been e.

Profibus is OK but I prefer Device Net quite frankly.

Ken I found DeviceNet to be fairly simple to use once it sunk into my thick head how the messaging worked.

The issue you may have with DNET is an interface for the systems. You should determine if all them offer a DNET interface, I dont see Foxboro or TI in the manufacturer list.

You can goto www.odva.org and it offer detailed information on what DeviceNet is and how it works. There is also a product list of most companies that offer DeviceNet products.

Thanks Ron,

Foxboro is beta testing a device net FBM, along with several other protocols (opc, ab ethernet), and they are due out sometime first qtr. next year. I've been burned by Foxboro promises in the past, so I'll believe it when I see it. They already have a modbus interface and I'm going to push for that because I know it works, and I've used it before.

FYI
CTI makes a devicenet card for the 505 series, we are currently using CTI modbus cards in our TI plc's with great success.

Ron since you have device net experience, for future projects would you recommend it over RIO. We currently use RIO for VFD's, Scales etc...

Oh my gosh yes.

Something else that might interest you is AS-i, especially if your systems require alot of wiring over distances.

You can get info on AS-i here: http://www.as-interface.com/

We did 2 conveyor/packaging lines that used DNET to communicate with the AB 160 drives and panelviews but the I/O were with an AS-I interface. Just one cable handles data and power for the I/O devices.

We used IFM electronic sensors and components and they were great.

I have also used DNET with other brands like Horner, www.heapg.com, and Toshiba drives. The only problems I had with that was being given the wrong part(s) and having the plc in idle/stop mode...long story but the DNET part was simple overall.

Is ethernet an option?

Messaging using ethernet is pretty straightforward on the setups we use (SLC 5/05 and Micrologix), but they are all local and share a subnet without very large amounts of data, so i don't know how it would work long distance...

but i do know the senior controls engineer on the other coast of the country has no problem doing online edits through the companies VPN. kinda creepy to know that someone three thousand miles away can start and stop your machines.