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

[JollyGreen]

I have a single run of about 135' I need to run to a panelview on a PLC5. Has anyone ever run a single drop line longer than 100' and had no issues?

 

[TConnolly]

Sometimes DH+ let's you get away with out of spec networks. Sometimes it doesn't. The specs are conservative so you may get away with it. If you try it make sure you use a terminating resistor.

 

[JollyGreen]

Thanks, anyone else had success with drop lines over 100 ft?

 

[geniusintraining]

I have and never had issues... not sure of the exact length but guessing I would say 100-150... like TConnolly said the resistors are a must, I only had about 10 nodes on that network

 

[JollyGreen]

OK, thanks guys. I will try it with terminating resistors. 150 ohm since I am at 57k.

 

[Ken Roach]

At 135 feet, it's really a 'star' configuration and not a dropline. The signal at that distance is going to depend on the loading from the rest of the network daisy-chain.

I do not expect it to work reliably.

Once you've thrown out the basic principles of the network, you may as well treat it like an engineering project. Connect a scope to the junction where you're going to add the 'dropline', and get a look at the signal quality there. Then add the new network leg and take a look at the signal waveform at the extreme end. Try without a resistor, and with a 60 ohm resistor, and with an 82 ohm resistor, and with a 150 ohm resistor. This is tricky because you're never sure which node's data you are seeing on the scope, and for the network to function properly each device must see valid data no matter where it is located on the network.

I have seen installations like this, where a 'dropline' was run 50 to 80 feet to a PLC or PanelView that was added to the network, that worked marginally for years.

They were able to improve those installations with a Weed Instruments (owned by Ultra Electronics) EOTec 2000 repeater.

These devices are built to be fiber-optic repeaters but can be connected with their copper modules only to be a DH+ 'hub'. The 2C12 model can give you a nice clean DH+ signal that you can run for another 10,000 feet.

 

[sthompson]

Perhaps the Manual for the 1770-SC DH+ Drop Station will help you out.

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1770-td020_-en-p.pdf

Stu....

 

[JollyGreen]

I appreciate the input. I planned on scoping it, and it is a panelview. The trunkline has a really clean signal.

 

[daba]

If you are taking your "drop" from near the end of the "trunk", why not make the end of the existing "trunk" the "drop".

Move the terminating resistor that should be on the end of your existing "trunk" to the far end of the "drop", which now becomes your new "trunk".

I can't see any problems with the distances you are talking.

 

[TheWaterboy]

I have one that is probably 300 feet, direct burial. Between 2 ML1400's. Never given a problem. Kinda hoped it would so I could justify a fix but it keeps on ticking

 

[Ken Roach]

If it's point-to-point and is between MicroLogix 1400 controllers, it is neither DH+ nor a dropline.

If yours is DH485, that's well within the 4,000 foot limit. If it's RS-232, then you have an impressively over-the-limit installation that I am also surprised by.

 

[TheWaterboy]

I know you are right, I do believe there is a485 adapter on each one... but prior to them being ML1400's they were PLC5's and I sure thought it was DH+ between them... I'm using the same blue hose for the 485 connection now.

 

[Ken Roach]

Ah, they're probably using RS-485 with 1763-NC01 cable adapters (to connect to the RS485 pins on the MicroLogix 1400 controllers).

The 'blue hose' will probably work for RS485. It's not optimal because there's no dedicated signal common (I'll bet you a donut they're using the shield) but it will probably work.

 

[daba]

If you are taking your "drop" from near the end of the "trunk", why not make the end of the existing "trunk" the "drop".

Move the terminating resistor that should be on the end of your existing "trunk" to the far end of the "drop", which now becomes your new "trunk".

I can't see any problems with the distances you are talking.

Well that was when I thought it was DH+

 

[geniusintraining]

At 135 feet, it's really a 'star' configuration and not a dropline.

Guess I don't understand a Star and Drop/Trunk Line then...

This is what I had, the longer one on the right was more then 150' at the end of every line was a resister and a node, 3 PC's running RSView 32 and 7-9 5/04's

We never had any issues, I would of said the long one in the middle was the trunk and the branches coming off were drop lines and I would of called a star more in the shape of a start going from node to node