Has anyone ever run a dropline over 100 ft on a DH+ system?

[Mickey]

See link

http://www.webopedia.com/TERM/S/star_network.html

 

[JollyGreen]

I agree with Genius Training as to the definition of trunk going up and down with all the left and right branches being "droplines"
They are all PLC 5's with DCM modules in DH+ "about 30 nodes in all"
I think one branch or "dropline" being 130 ft or so added to the trunk should be just fine.

 

[Ken Roach]

GeniusinTraining: That's a reasonable architecture for a trunkline/dropline network.

But it was badly overterminated. It should have had only two termination resistors.

I wish I had a succinct way of saying "the successful operation of some incorrectly installed networks does not prove that all incorrectly installed networks will be successful".

 

[geniusintraining]

I wish I had a succinct way of saying...

"If it works"

 

[Ken Roach]

I have been known to argue with success.

 

[geniusintraining]

 

[Gil47]

Our busiest DH+ network used to have 15 nodes on it and over time we dropped that to 10 nodes by some Ethernet updates, on a trunkline, dropline setup, and a terminating resistor at each end of the trunkline

This network was extremely slow and near impossible to program over from Ethernet to DH+ nodes

By removing the droplines and making the network totally trunkline by doing cable diversions of unused existing cables we found we were getting better performance with each one of our tidy ups to the point that when we program on the DH+ from Ethernet now we look like its all done on Ethernet its been a massive improvement

We were not seeing problems in error tables before or after our changes just improvements in access times.

So I am backing Kens assessment do your network with little or no droplines if you can.

 

[Gil47]

Just to clear up any confusion I left in my previous post,
the Ethernet to DH+ was via a Control Logix Gateway

also
Most of the droplines we removed were no longer connected to a PLC or Panelview.

 

[daba]

DH+ (and RIO, same technology, different protocol) is a very forgiving network.

Sure, there is the "correct" way to install and terminate it, and the "correct" way is well documented.

However, getting down to fundamentals...

The purpose of the terminating resistor at each end of the "trunk-line" is to suppress signal reflection. When the transmitted data reaches a "dead-end" some of the signal is reflected back along the trunk-line, which interferes with the signal coming at it.

Consider that each node on the network, even if daisy-chain connected, has a "drop", from the terminations to the transceiver circuits. These are very short, so any signal reflection caused by the high impedance of the transceiver circuit is "in-phase" with the signal on the network, and any interference will be negligable. BUT, the last node on the cable, or the trunk-line just after where the last node is "dropped" needs a terminator.

I would suggest that whatever the topology, if you were to make sure that you have a terminating resistor at the end of each long run, then you may well be able to use a "star" configuration. I've seen it done several times with no issues.

Of course, RA tech support will only support networks installed "to the book", but when push comes to shove, and you just have to hook-up in a non-standard way, just think about where a terminating resistor should be installed.


On a side note : in a brewery I did a lot of work in, one DH+ network would go "intermittent" at roughly the same time, once a week. It was a puzzler, because the network had been installed to the book, using a high-level trunk-line, Station Connectors, and drops in galvanised conduit to the control panels.

Eventually, after the brewery engineers had failed to find any problems, RA Tech Support were called in. They did signal strength and quality measurements at various places on the network, and couldn't find anything wrong. So they did a full physical survey.

What they found was a drop into a decommissioned control panel was still connected to the trunk-line, there was about 15 foot of "blue hose" coiled up in the bottom of the panel, and the bare ends of the conductors were just sitting there.

The reason why the network went bad at a specific time in the week was due to scheduled cleaning of the area with high-pressure washers. The decommissioned panel had had all its push-buttons, switches and lamps removed from the doors when the internal kit was removed, so there were lots of holes for water to get in.

The survey found the coil of blue hose (with its bare ends), sitting in a pool of water in the bottom of the old panel !!

 

[JollyGreen]

This is proving to be a much more interesting thread than I initially expected.