DH+ vs Profibus for Peer to Peer on AB


Thread Starter

Scott J.

Dear List,
I am setting up 10 AB PLC 5/30s.
Which would be the better way to connect for Peer to Peer comm; Profibus or DH+? I understand profibus is getting to be a world standard, yet DH+ is AB's "best" way of doing things. I would like to leave room for expandibility at a reasonable cost, (not changing network design down the road). Is it true that most manufacturers
are making there *products profibus ready and ignoring AB's protocols? (*products like scales, HMIs, Chart Recorders, and other devices one might add on to a control network.) I understand that DH+ works fantastic, yet I don't want to limit ourselves if everything is going Profibus.
I really appreciate your input on this.
Thank you In advance,
Scott J.
[email protected]
"The Lightning Man"

R A Peterson

1. Is there even a Profibus connection available for AB?

2. DH+ is built in to PLC5s. It costs nothing to add it.

3. All of the devices you mentioned have DH+ connectivity available (except maybe the chart recorder).

Bob Peterson

Andrew Piereder

Without bogging down in too much technical detail; Profibus encompasses a number of different protocols, the most common of which is Profibus DP. DP is not in fact a peer-to-peer network, but rather as the designation suggests, a protocol designed for decentralized peripherals, or I/O. When people refer to Profibus, at least in North American, they are generally referring to Profibus DP. SST manufacturers a module for the SLC and PLC5
that allows the controller to communicate with Profibus enabled peripherals. You can also use DeviceNet and Interbus for many of the same applications.

DHP is a true peer-to-peer protocol designed, not for I/O control, but for messaging between controllers. There are some excellent diagnostic tools available and its still a very viable network for most common applications. In more and more cases though, it is being supplanted by TCP/IP Ethernet which does the job as well or better in some cases (although in others, DHP
would still have an edge because of its industrialized qualities). Just to make it even more complicated, ControlNet is also a viable option with both messaging and I/O control capabilities.

In all likelyhood, you would probably want to consider using both Profibus DP and DHP or their alternates--one at the I/O level and the other for

Andy Piereder
Pinnacle IDC

Kirk S. Hegwood

My 2 cents worth, if you go DH+ you're stuck with AB. We are in the process of trying to migrate away from DH+ and AB.

Kirk S. Hegwood
Signing for Hegwood Electric Service, Inc.