Is it possible to configure 2 nos of 1756-CNBR in one rack?
- Thread starter mr_zul
- Start date
Ken Roach
Lifetime Supporting Member + Moderator
Welcome to the Forum !
While you can certainly install two or more 1756-CNB(R) modules in a ControlLogix I/O chassis, the modules cannot be configured to automatically act as redundant backups to one another.
You need to either adjust your expectations of what ControlLogix redundancy can do or choose a different I/O architecture like Bulletin 1715 fault tolerant I/O.
While you can certainly install two or more 1756-CNB(R) modules in a ControlLogix I/O chassis, the modules cannot be configured to automatically act as redundant backups to one another.
You need to either adjust your expectations of what ControlLogix redundancy can do or choose a different I/O architecture like Bulletin 1715 fault tolerant I/O.
And, in addition to Ken's excellent reply, if your application requires such a high level of redundancy that you considered putting 2 CNBR's in the same chassis, what about the chassis itself?, and of course its power supply?, and not forgetting the I/O modules !!
It is a difficult and costly exercise to completely eradicate a single-point of failure
In my system, my power supply modules are redundant but not the IO modules. Willing to accept certain level of failures but not single failure of communication.
Is there a ref document or link to support this quote?
Anyway, thank you for your reply. I will read up the Bulletin 1715 fault tolerant I/O as you mentioned.
But your backplane is also a communications network - that itself will give you a single-point of failure.
Well that would be considered chassis failure, which I am willing to accept
rdrast
Lifetime Supporting Member
For what it it worth, out of 50 or so Logix racks here, all with ControlNet for the IO, in the past 6 years we have had:
0 Processor faults
0 1756-CNB faults
0 1756-CN2 faults
2 ControlNet Cabling faults
1 1756-ENBT faults
0 1756-EN2T faults
0 1756-EWEB faults
MANY Ethernet Network/Cabling faults
0 1756- Any Power supply faults
and
4 1756-A13 failures
3 1756-A17 failures.
Going for redundant redundant ControlNet bridges seems a complete waste of time, but it's not my time.
Ken Roach
Lifetime Supporting Member + Moderator
The reference documents that describe the configuration of ControlNet I/O racks and modules with Redundant ControlLogix are:
ControlNet Modules in Logix 5000 Control Systems
CNET-UM001
ControlLogix Enhanced Redundancy System User Manual
1756-UM535
You may also want to review such documents as "Achieving High Availability in Process Control Applications", publication PROCES-WP004 and even the newest Redundancy release overview for v19.50, publication 1756-PP017.
I do not know of a document that discusses in detail why you cannot use two 1756-CNBR modules as a backup pair in an adapter rack. It's simply not how the system works.
ControlNet Modules in Logix 5000 Control Systems
CNET-UM001
ControlLogix Enhanced Redundancy System User Manual
1756-UM535
You may also want to review such documents as "Achieving High Availability in Process Control Applications", publication PROCES-WP004 and even the newest Redundancy release overview for v19.50, publication 1756-PP017.
I do not know of a document that discusses in detail why you cannot use two 1756-CNBR modules as a backup pair in an adapter rack. It's simply not how the system works.
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