Contrologix PLC I/O and Flex I/O

DearExpert,
i have a project that requires me to use a dual redundant PLC spec.(Power and CPU redundancy).
i will like to use rockwellAutomation as my brand, going through i see that contrologix will suit my purpose, how ever in the redundant architecture i saw, they included contrologix I/O module and Flex i/o module.My questions are....
1. why the two i/o modules?
2. Any other AllenBradley PLC with this kinda redundancy features?
3.All i wana do is monitor or possibly control Field devices, is contrologix no two much for this task?
My I/o counts are
total D i/o= 95
A i/o = 158
each with a mix of different voltage requirement 24vdc, 120 VAC, 4-20ma
Kindly advice on what /how to spec things out here .

Please take Redundancy seriously.

Read and understand the ControlLogix Enhanced Redundancy System User Manual, Publication 1756-UM535.

ControlLogix Redundancy can use any I/O platform that has a ControlNet adapter; Bulletin 1756 ControlLogix I/O, Bulletin 1794 FLEX I/O, Bulletin 1734 POINT I/O, or even Bulletin 1771 PLC-5 I/O, as well as drives, power monitors, and network bridges that connect to ControlNet.

While some other Allen-Bradley controllers do have some degree of "hot backup" functionality, the ControlLogix is the only controller that provides redundancy for the power supplies, the CPU, and the I/O network.

Whether or not an SLC-500 or CompactLogix system with "hot backup" I/O scanning modules will suit your application and specification requirements is a decision that is up to you.

Hi Ken,
Thanks a Lot , this has really helped me, but there seems to be a lot of acessories to be picked ,added to have a complete list ...(thats from the Rockwell end/site).........

Thanks

While I agree with Ken, that this is a serious issue, I disagree with the sincerity of the request, based on my experience.

I've had a number of clients who thought they wanted redundant PLC controls. Sadly, they didn't know why. And, when told the expense, most simply say "forget it".

When you do a bit of analysis on the items most likely to fail, the PLC hardly makes anybody's list. Its protected in an enclosure, not subject to failure like field devices. Moreover, the amount of infrastructure need to support 'a PLC that never fails' is not small. Add to that the disciple needed on the part of the programmers and technicians to avoid 'the man with two watches' syndrome (software changes).....

Now, before a flame-war starts, yes, I will grant that some and certain processes (Glassmaking, steelmelting) do demand a certain level of uptime to remain safe.

But, for the majority of the rest of the world, this stuff is just Super Wham-O-Dyne extra work and hardware that will likely never get used.

Ken Roach said:

Please take Redundancy seriously.

Read and understand the ControlLogix Enhanced Redundancy System User Manual, Publication 1756-UM535.

ControlLogix Redundancy can use any I/O platform that has a ControlNet adapter; Bulletin 1756 ControlLogix I/O, Bulletin 1794 FLEX I/O, Bulletin 1734 POINT I/O, or even Bulletin 1771 PLC-5 I/O, as well as drives, power monitors, and network bridges that connect to ControlNet.

While some other Allen-Bradley controllers do have some degree of "hot backup" functionality, the ControlLogix is the only controller that provides redundancy for the power supplies, the CPU, and the I/O network.

Whether or not an SLC-500 or CompactLogix system with "hot backup" I/O scanning modules will suit your application and specification requirements is a decision that is up to you.

Click to expand...

The OP may not have the authority to argue with the requirements or spec. Don't get me started on spec writers. It's like the story of the Emporers New Clothes. Everyone is afraid to argue or complain. Why are these guys untouchable. So much taxpayer money has been wasted over these guys writing in Caddilac specs. Some of them are obviously lazy and just mail in the same boiler plate spec time and again not realizing that listed equipment is obsolete.