I have a clx system where remote racks are connected via controlnet. I believe what i've seen/done on past projects was to install 1 CNB module per remore rack. So if i have a main rack and 2 remote racks, I would need 2 CNB's in the main rack, and 1 in each remote rack. I was told, however, that I only ever need 1 CNB module in a rack and that I wire all the other racks in series. Are both possible solutions, and if so, what are the benefits of each? Thanks.

Rockwell has several installation manuals in their literature library.

Nornally you wire a trunk line wit terminating resistors at the ends and drops to each CNB.

There are limits as to how many "slave" CNB's you can assocaite with a single "master" CNB.

These limits are due more to bandwidth and response times than CNB count.

Again I'd read the manuals for an involved isntall.

For your case 1 main rack CNB and 2 Remote Rack CNB's with 1 per remote rack should not be a problem.

The only way I have done this is to have only one 1756-CN2 in the Local Chassis, then the subsequent remote racks have one 1756 CNBR's, (we had a redundant network) daisy chained together with a one meter T-Tap. The only instance I needed to add another 1756-CN2 in the local rack was when the customer requested it, I beleive he was going to communicate to another rack that had another processor in it...

As far as which method is better or worse, I think both are dodable however, you may be spending more dollars for a module you don't need, by adding two in the Local rack. Scheduling the Controlnet network might also be more of a headache with two bridge modules in the local rack when you really only need one.

Hope this helps

You only need one ControlNet Bridge module in the main rack, as long as it can handle the required number of "Connections".

The 1756-CNB® modules can handle 64 max connections, while the 1756-CN2® modules can handle 128 max connections.

I have one system with a CNB that is maxed out, running 15 or so remote I/O racks, but it runs fine.

The only time I add multiple CNB's is if I have a great deal of I/O, or I want to split off segments. Generally, if I'm using a bunch of remote I/O and networked drives, I'll put all the I/O on one ControlNet bridge, and the drives on a second.