DH+ or something better?


Thread Starter

Trevor Ousey

Hello list,
I just want to raise a discussion on better networking with A-B plcs.
I am currently doing upgrades at a factory site, with multiple A-B plc's,
one area having 3 plc5's and 5 slc5/04's, with Intouch and a Panelview,
all on one DH+ network. The baud rate is 57.6k, minimal message functions
occurring, but it is slowing down dramatically while doing online editing.

We are going to be upgading several more areas, and the plan was to
use DH+ but it doesn't seem like the best choice. I would like to here the
views of people who have tried other solutions, ie ethernet, ControlNet.

The overall plan was to have all the area networks linked via a
gateway, also with a IS network to all the Intouch PC's. Also any
with the gateway would be appreciated.

Trevor Ousey
Kalangadoo, South Australia
I have used ControlLogix Gateway several times. It works well and A-B has made improvements in regards to ease of implementation. We have successfully bridged DH+, Ethernet,and ControlNet all one the same Gateway. One possible GOTCHA. When ControlLogix ENET module first came out it used a different Ethernet protocal than did the PLC’s with Ethernet (one was EPIC and I forget the other). The result is that the PLC could not communicate with the Gateway. This was changed in later versions (about 4th quarter ‘98) and there is a firmware upgrade for older modules so that they both use the same protocal.
You can increase the baud rate on DH+ up to 230k if you are using newer processors. However, that is its limit. ControlNet provides more bandwidth and offers built in redundacy. Ethernet works fine too. Just do not connect directly into your business networks. One solution you may consider is Modbus plus. Prosoft makes Modbus plus modules for both the 1746 and 1771 form factor. I have found it a great solution to take advantage of an installed base of exisitng processors that may either not have free comm ports. It offers 1Mbit and Prosoft now has a Modbus TCP/IP module with even more bandwidth but I have no experience.
Typically, I the deciding factor is cost to install the network. If money is no object
I like Ethernet best on non-mission critical systems. ControlNet’s redundancy
definately has its advantages when the network must be up. Also, I am not yet
aware of an Ethernet PanelView, although it has been promised by A-B

Leighton Toews

Allen Bradley networking...
Ethernet: Beware that the processors below the 5/40E are afflicted with an annoying little bug where if you perform a search while editing online the ENTIRE PLC memory will be wiped clean.
If you are bogging down your network while editing online you could try increasing your communication speed, depends somewhat on your trunk length but most plants I have dealt with have been able to achieve 230kps, especially if there is minimal network traffic.
I have worked with ControlNet, DeviceNet, EtherNet and DH+ - the first thing I would try if I were you would be to increase your communication speed, this would be the most inexpensive solution and will likely work fine for you.
Leighton Toews
Automation Technologist
Deltech Industries Inc.
“Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.”