devicenet over other cables (dh+ cable)

Guys is anybody running DN on other media types other than those designed for DN use possibly DH+ ?

we have an application on some mutlipurpose overhead gantry cranes in an Aluminium smelter where the cabin & tools rotate 360deg independantly of each other all cabling is via sliprings which are not accessable without major disassembly of the cranes.
originaly Data highway & remote i/o networks are these cranes.
we are going to undertake a PLC upgrade from AB PLC5 to Control logix & are wishing take advantage of DN fuctionality on these machines & remove the DH+ & RIO.
the sliprings installed meet the criteria for DN use other than the cable 3m on each side of the sliprings.

The proposal we have is to install the DN network as per the usual method but use DN-Fibre convertor to fibre patch lead then Fibre-DN convertor onto the DH+ twinax through th sliprings then the same onthe other side.
the use of the fibre-DN will do away with any impedance mismatch as well as provide an electrical insulation level which is bonus.

Your thoughts?
Will it work?

thanx
Scott.

I hope you realize that whatever devices that are connected to the crane are going to have to be converted to DN devices (or hooked up to a DN remote I/O block).

To answer your question, it will work as long as you have 4 wires running to the devices. But how are you going to connect the drop cables to the trunk? If I remember correctly, the DN trunk cable has a Red-Black pair for power and a Blue-White pair for communications. I've never used the Fibre-DN converter, so I'm not sure exactly how that would work.

Experiment !

Try to make a similar configuration as the one that you want to use and see if it works.
As you are only talking about 3 meters, it is probably not so critical what type of cable you are using.
(In the past have tried to make DH+ work over semilong distances with some screened cable that was available - no problem).

We have used device net over a single twisted pair for the data pair and used a seperate power supply at each node, it has been in service for about 4 years now over about 500m, no problems.

Your post gave me the willies.

DeviceNet is so sensitive to media conditions that I would have strong reservations about trying such an arrangement. I've heard of DeviceNet being theoretically routed through slip rings, but I don't know of anyone whose done it successfully.

Sounds like a question for Dr. DeviceNet over on the ODVA.org site...

No... I doubt that you will be able to get both sections to act as if they are on the same network because it is critical to the integrity of DNet that all the node clocks are synchronised. If the link across the slip rings isn't very fast then there is no way for the two sections to synchronise their clocks.

The Dnet/Fibre convertors work because their throughput is very high, but as soon as you introduce any other convertors to allow for a copper connection through the slip rings, the increased throughout will probably cause the scheme to fail.

PaulC20,
I'm interested in your DeviceNet application mentioned below since I am looking at a similar situation and the client wants to use separate power supplies with a single twisted pair for DeviceNet comms. Please e-mail me at [email protected] with contact details.

paulc20 said:

We have used device net over a single twisted pair for the data pair and used a seperate power supply at each node, it has been in service for about 4 years now over about 500m, no problems.

Click to expand...

I once installed DeviceNet RFID readers in multiple conveyors that feed back to one main Compact Logix PLC. Each reader pulled 24vDC from it's respective conveyor.

Problem was that if you killed the power on any of the conveyors, you sent the DeviceNet into an error on the Main PLC and the entire machine shutdown.

Best bet is to keep all of your DN modules on one power supply unless it is impossible, like the 500m example.

Devicenet is usually fussy as per cabling standards and is extremely susceptable to electrical noise from motors, servos and VFDs. That said, I have been successful using any old cable for short distances in my office and have once used two spare - 2 conductor shielded cables which were routed through power cables, wire duct etc. I used the lowest communications speed and I got away with it even though I told everyone it would never work. I have also seen properly wired systems which would shut down devicnet cards on a regular basis due to traffic and errors on the system.