DH+ Network splitting

This is for an A-B DH+ network with SLC5/04 and KE-1785 modules connecting with a Honeywell DCS.

I've been trying to split a DH+ network with about 25 nodes on it. I took out a small jumper in the middle of the network and place 150 ohm terminators on each new end. After splitting only one side saw all of it's nodes, while the other side only saw the first 4 nodes. After checking all of the conncections on the side that did not come back (per Rockwell's reccomendation), I had to recconnect, and all the nodes came back fine. With all of the nodes hooked together we don't pick up any errors looking at RSLinx.

Other than calling out a Rockwell field tech, I (and my peers) are out of ideas on what to check. Are there any special methods to doing this? The best info I can get says that it shouldn't be a token problem as the lowest number node should generate one.

NOTE: Splitting is required for us because we are adding a new node (another SLC5/04) that is adding 2200 ft+ to the network lenght and we lost half our network when tying it in, so we think we were exceeding the 10K ft limit.

the other side only saw the first 4 nodes

Click to expand...

First 4 node-number-wise, first 4 from the new terminating resistor, or first 4 from the location of the PC interface ?

What precisely do you mean by "don't pick up any errors using RSLinx" ?

Likely this network isn't a straight daisy-chain installation and you'd be spending worthwhile money having somebody with experience, an analyzer, and an oscilloscope looking at it.

Dumb questions...

1) What's the speed of the hwy? 56 or 230…150 ohm for 56 and 82ohm for 230

2) On the nodes that are not working, are the hwy LED's solid? (on)

3) Your "terminators" are they just resistors? Or are they 'special'?


I did this about a month ago and had no issues, but my system is a straight daisy chain style, do you have a drawing of your system?

Look at all of your nodes see if they are (all) double up under the terminals except the end of the line, the end of the line should have the resistors, that's how I understand the system to work (someone will tell me if i'm wrong, thats a given), but there are other methods, I’m not familiar with them.

Hope this helps, let us know what you find

There is a trunkline drop line method as well. AB makes a 1771-something that allows you to set up a trunk line drop line configuration for DH+. I used one of these once when we found (at a customer site) that they ran out of blue hose between connections and wire nutted the trunk up in the ceiling on top of a flourescent light ballast. It was an effective way to fix the problem and I think it had a selectable terminating resistor switch built in if it was at the end of the line.


Marc

The first four nodes were as seen from the terminating resistor.

Our speed is 56K and we used 150 ohm resistors, nothing special about them.

Our system is set up daisy chain, with trunklines on most, but not all nodes.

The weird thing is that the whole network works fine, the part that doesn't work is okay on the original network, but when split it doesn't all come back.

Unfortunately, we didn't have time to check the DH+ lights on the nodes that didn't come back as the operation locked in a lot of alarms for the plant operators (loss of signal) and they demanded to get the situation cleared up as quickly as possible, so we weren't allowed to work it on anymore at that point. (any of you other guys run into that?) The plant will come down for a maintenance turnaround in the middle of January when we should be able to tackle this again.

Marc said:

There is a trunkline drop line method as well. AB makes a 1771-something that allows you to set up a trunk line drop line configuration for DH+. I used one of these once when we found (at a customer site) that they ran out of blue hose between connections and wire nutted the trunk up in the ceiling on top of a flourescent light ballast. It was an effective way to fix the problem and I think it had a selectable terminating resistor switch built in if it was at the end of the line.


Marc

Click to expand...

FYI
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1770c-in002_-en-p.pdf

Mickey,

Thats the one, I think it may have been updated though, I don't think it came with the PLC 5 conector and it may have had another resistor for higher speed DH+ 82 or 83 ohm but I could be mistaken.

Marc