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Old August 30th, 2006, 06:57 AM   #1

rajsiyer is offline
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Unhappy AB DH485 network problem

Hi friends,

Please take a look at the diagram attached..

Th PLC circled in red, i.e. Node2 can't get connected. If it's connnected to the 1747 PKTX's network, all other PLCs go offline. By itself it can be connected to the PC with InTouch and shows up on RSLinx. Problem is.. after properly configuring it to communicate with RSLinx/InTouch (by assigning it its Node ID)and linking it with the network, all other PLCs lose communication. It disturbs them all!.

To figure the problem,

I've Interchanged ALL the NET-AIC cards and found that they all work properly.

Next I've Interchanged the PLCs(With Racks, not merely the CPU cards) and found that the problem persists irrespective of what PLC you might connect at that node.

The Problem does not resolve or even worsen, whether you attach the termination resistors at the 1st or last PLC on the bus or for that matter on the problematic PLC at Node 2.

3. There's no problem or error indication in the program inside PLC at Node 2. It is in Run Mode and data is visible at the RS-view PC.

4. Disconnecting the Node 2's DH-485 from the RS-view network does not help. Infact, when Node2 is connected as a single PLC on the PKTX network, it shows up nicely on RSLinx, InTouch PC and also the RS-View PC at the same time.

At present, we get by, disconnecting the RS232 link between the Net AIC card of the Node 2 PLC. It is running and its data is utilised on the RS-view application, without problems. Only issue here is that it disturbs the upper network.
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Old August 30th, 2006, 08:03 AM   #2

SNK is offline
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To keep things simple, have you re-assigned your original node 2 as something different, say 25?
(you will obviously have to change your Messaging if used as well to suit)
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Old August 30th, 2006, 09:08 AM   #3
Thomas Sullens
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We had the same problem it turned out to be a faulty 1747 aic. It would work by its self, but when put on the network everything crashed. You might swap these cards around and see if your problem moves. I would put a new 1747 aic on node 2.
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Old August 30th, 2006, 09:18 AM   #4

rajsiyer is offline
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A big thank you, for your prompt reply.

We took care to ensure retaining the node ID as 2 on whatever PLC was substituted in its place as also to keep the same application(PLC prog)as earlier. Mind you, the node IDs are used in device-tags for SCADA Signals. As the SCADA application is fairly large with many scripts etc, Changing the Node ID is something we have deferred attempting.

Please also see this link.

this one is vexing me for a long time now

Regards, best of luck and wishes..
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Old August 30th, 2006, 09:19 AM   #5
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I am wondering, the PLCs are numbered 1-8, what node address are the PC's using since both are on DH-485 according to the drawing.

I would do what SNK suggested and check node addressing and/or change to a higher number to see what happens.
__________________ Industrial Electrical & Maintenance @ "Tell me and I forget, show me and I remember, involve me and I understand."
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Old February 6th, 2008, 01:27 AM   #6

akoraz is offline
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hi raj
Not far from the subject I have a communication failure between a Modicon TSX37 PLC's ( UnilTelway) since I lost the communication between the plc's
need your assistant
contact me at \
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Old February 8th, 2008, 09:00 PM   #7
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CJones is offline
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What card is in the other computer?

I have three computers on my little DH+ network one with the ptkx and two with the kt (ktx?) it seems the cards don't like eachother and I do know that the old cards had an internal resistor and I wonder if that hasn't been giving me my problems?

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