Multiple SLC 5/05 Processors in one rack, for backup

Hello everybody, have question: my customer wants to have hot backups of his 5x SLC 5/05, Can I install them in one rack and keep in prog mode, update program in case if production plc were updated. and let him monitor battery light?

Never mind, just tested:
battery light not coming on, if battery disconnected.
rslinx can't discover plc

If his process is that production critical, he needs to start investing in replacing that with newer technology.

I'll be happy to do it, but their maintenance manager bought 5 spare PLCs from ebay. And he believes it will solve all problems with water leaks via pipes in PLCs cabinets

You can't have multiple processors in a SLC rack.

He can keep them in the parts room and installed when needed.

If the maintenance manager thinks that keeping a powered-on spare next to a running unit is an effective way to protect against water damage, you need to take him swimming and pull him underwater for a few seconds to prove your point.

Anyhow: SLC controllers can only be placed in Slot 0. The power and signal architecture of the 1746 chassis simply doesn't allow for multiple CPUs to be inserted into the backplane.

In ControlLogix 1756 series controllers, you can have multiple CPUs in the chassis, but you would end up having to do something complicated with connection inhibition in order to keep them from competing for modules. Redundancy in ControlLogix is not done in a single chassis.

You understand the principles of SLC-500 disaster recovery: keep the backup CPU safe and dry, and keep good archives of the operating program.

I personally think that efforts to keep a CPU running and loaded with the active program or to keep the program held by a battery are suboptimal; you're wearing out the components over time with heat, or shortening the in-service life of the battery.

And to clarify....a SLC processor will physically fit in any slot. But look at the connectors on the CPU compared to the chassis itself and you'll see that only slot 0 has additional connectors the CPU requires.

OG

1747-BSN - Backup Scanner Module...

SLC Backup Scanner (1747-BSN) module option...

1. You have specified SLC 5/05 processors X

2. There are likely to be local I/O modules used X

3. Redundancy would require duplication of the entire chassis or chassis' X

When I read this thread I initially thought of the above module but, after further consideration, and in particular the above points, it would not be suitable.

1. It does not provide redundancy for Ethernet communications

2. It does not provide redundancy for local I/O

3. It would require duplicate chassis configurations which may prove cost prohibitive

Still, I think it important to mention it's existence, lest folks think there may be no redundancy options available to the SLC platform...

19378 - 1747-BSN Frequently Asked Questions
Access Level: TechConnect

However, even if there was a suitable redundancy method, and more specifically one that allowed a failover secondary processor in the same chassis as the primary, I would not recommend it here. For similar reasons to others, it would not be the best way to combat the ingress of water to the enclosure. This sort of thinking should really not be entertained. If water is able to reach the chassis, and let's say both a primary and secondary processor are located in this same chassis, then it would be highly likely that any water attributed damage could potentially take out both processors at once i.e. the whole chassis is exposed to the possible risk.

I would advise as aforementioned - keep the spare SLC 5/05 processors on the shelf and realize the impact in time to swap out in the event of a failure. But remember, with water, it may not only be the processor that ends up damaged. Other modules or even the chassis itself could also need replacing. You would have to carry a full compliment of spares for the entire configuration.

The best recommendation, in my opinion, is for them to try and resolve the water ingression issue. Or move the equipment, if at all possible. If that cannot or realistically will not be acheived here, and redundancy is the only option, then you would have to migrate the entire system to a redundancy compatible platform where the backup chassis is remote from the risk. But, if that were achieved, then it could be argued to just run the system from the remote location instead, without any redundancy.

The spare SLC 5/05 processors are, I'm afraid, exactly that - spares.

P.s. The battery LED indicator (BAT) should illuminate when the battery is disconnected or low. Also, the battery low system bit should be set. It is possible that a 1747-BAJMPR battery jumper is in place, which prevents the BAT LED from coming on?

Regards,
George