AB DH485 problem

Shawn Cassidy

Member
Join Date
Mar 2004
Location
Montreal
Posts
98
I'm having a problem with a Allen-Bradley DH485 network. I have 1 SLC5/03 master (node 1),2 ML1000's (node's 2&3)on my network. Everything works fine until.... someone turns the power off on one of the ML1000's. While monitoring the network using RSLinx the ML1000 is off the network when the power is lost (what is expected). When the power is restored the node does not come back into the network. If I cycle the power on the other ML1000 it will get back onto the network. To reset the network I have to turn the power off on the ML1000 and the SLC 5/03. Restore power to the ML1000 wait a few seconds them turn the power back on for the SLC 5/03. When this is done all the nodes in the network are present. The ML1000 that is having the problem is the last one connected in the network chain. They are connected in a daisy chain. I've checked the connections and everything appears to be fine (jumpers). There are no duplicated nodes and communication settings in each PLC seem to be OK. I hope someone else has had a similiar problem. I've looked through threads relating to DH485 but haven't been able to find a solution.
 
I assume that your network is 5/03 > AIC > AIC+ > ML1000 > AIC+ > ML1000? If so, do you have the jumpers between terminals 1 & 2 and 5 & 6 at the AIC and between 5 & 6 at the last AIC+?
 
Actually, I'm just going over the jumpers again. I'll take a closer look and get back with the result...
Just verified the jumpers and they are OK.......
I have noticed that the number of nodes in the network is at 32. Will reducing this number of nodes make a difference?
 
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After re-checking the network wiring I discovered that an AB Adaptascan barcode reader was added to the system. It was not added to the daisy-chain but was added in parallel to one of the AIC modules. I disconnected the barcode and the problem is gone. I'll just add it to the daisy-chain and make it the terminating module..?.. Should work? It's an Adaptascan 2755-SN5 circa 1997.
 
Try reducing the number of nodes on the configuration in RSlinx, and in the downloaded configuration. I had a problem once with a slower laptop for some reason, I was using 4 nodes, and the last node would drop in and out every scan of the nodes.
 
Thanks.
I'll give that a try once I've rewired the barcode scanner into the network properly. I think the problem was the scanner added in parallel rather than in daisy-chain. It will help to reduce the number of nodes.
 
I finally had a chance to complete the wiring changes on the network. I put the adaptascan barcode as the last node (terminating). Funny thing is I still have the problem. The network works fine until any of my machines are powered down and then back up again they do not get back onto the network. They drop off and stay off until I power down the first network module. I read somewhere that the adaptascan barcodes should be the second node in the network (node 2). Does anyone know if this is true?
Also, does the length of the DH485 network cause a problem for the adaptascan? I know it shouldn't be more than 50' for an RS232 type connection. I'm thinking of rewiring the network so that the barcode will be node2 and not the terminating module. It's not an easy thing to do however since I'll also have to change the node addresses of each PLC on the network which means all the documentation has to also be changed.... If anyone has any ideas it would be much appreciated.
:(
 
I have my Adaptascan BCR all on a devicenet network. I currently have 8 on one SLC. I use DH+ and have never tried the BCR on DH or anything but a Basic Module. Here is a screen shot out of the manual that limits the distance to 50 feet without a link coupler. Also, the troubleshooting sections says to look at the terminations and only terminate the 2 end devices (not node numbers).

screen shot.jpeg
 
I found more info on the way the network has to be arranged as far as nodes order goes. It seems that the adaptascans have to directly follow the master PLC node 1. Meaning that if you had 2 barcodes, a master SLC 5/03 and a ML1000 on a DH485 network the nodes would have to go in this order:SLC node 1, barcode#1 node 2, barcode#2 node 3, ML1000 node 4. I have rewired this network in the above order (it didn't make a difference)and I'll be changing the node addresses order also. I'm hoping the node order will solve the problem. If this doesn't work.......
 
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