Nodes dropping on DH+ network

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Thread Starter

Anonymous

I have a DH+ network with 22 nodes on it. When I add one more device to the network, I start seeing nodes fall off the network. Can someone tell me if I have exceeded the maximum number of nodes for this network? If not, what could possibly be causing these nodes to drop?
 
Make sure you have the correct termination at the end of the DH+ network and there is no odd resistors installed on the DH+ connectors in the middle somewhere.
 
You have not exceeded the maximum number of nodes. You can go up to node 77 with DH+. I would check the length of your network. There is a 10,000 ft limit. I would check that.
 
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Bob Peterson

DH+ is pretty tolerant and you can cheat a lot, but the more nodes you have, and the longer runs you have, the more likely it is that cheating will cause you grief.

Bob Peterson
 
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Bradley Hite

Hello, The first thing I would do is analyze the DH+ diagnostic data. You do have a diagnostic file set up in one of the PLCs right? If not I would configure one at the first opportunity. The diagnostic file records a lot of very useful DH+ status and health data.

As someone else suggested the maximum node address for DH+ is 77. That is 77 in OCTAL format. With octal DH+ addresses from 00-77 available you have a total of 64 unique address numbers. What address numbers are currently in use on your network? What is the address number of the device you are attempting to add to the network?

As someone else also suggested DH+ requires terminating resistors at the physical network cable ends. These resistors must be 150ohm resistors.

I would double check the physical cable layout. Is the DH+ cable all legitimate DH+ "Blue Hose" cable? Is the cable all from the same cable manufacturer? Is the total cable length less than 10,000ft? Are all of the cable connections solid? Have you checked for frayed shield and signal connections? Is the cable topology daisy chain, tap drop, or is it something else? DH+ networks have to be either daisy chain or tap drop architectures.

Something else to consider. Depending on what you are using the DH+ network for 22 nodes is getting to be a lot of nodes for a DH+ network. Remember DH+ only runs at 57.6kbps.

Feel free to contact me directly if you want.

Bradley G. Hite
Intertech Inc mailto:[email protected] http://www.myplc.com
Teaching Practical Skills for a Technological World
 
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Trevor Ousey \(lists\)

As stated before you can have up to node 77, giving you 64 nodes. Things I would check is the network baud rate and length. DH+ is quite stable at 57.6 and I have come across networks with out terminating resistors operating fine. Check that you are not doubling up a node number, also check that the blue and white are the correct polarity. I had one network were one half was different to the other, weird things happened.
 
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I would check the LEDs of the devices, if there are PLCs see if the DH+ LED is on solid or flashing or red. Red usually means a duplicate node, green flashing means tokens are getting lost.

I would bet it is physical problem, either you have to many or to few terminating resistors, or adding an extra bit of cable changed the characteristics of your transmission line, or maybe just bad connection.

Mike Bunker
www.datalinktek.com / www.datahighwayplus.com
 
Octal 77 (64) is the maximum number of logical nodes on a DH+ network. Since the topology is a bus, each node has to be capable of driving all the nodes (fan out).
The maximum number of physical nodes on a network most likely is less than the maximum number of logical nodes.
 
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