Redundant System with SLC

[guillencito 0]

Hi All! Someone of you have an example of a program for a redundant system using SLC's (or another AB PLC)? This is because I'm involved in development of a redundant system, but I'm not sure about what kind of instructions could use, I think about MSG instructions is good, but, if i can use another logical sequence, or another special instruction. Thanx a lot!

[mgvol 0]

I have personally done "Hot Back-up" apps using PLC-5's; specifically you have to use ControlNet PLC-5's with a Hot Back-up module and redundant ControlNet network scanners/adapters. The 1756 ControLogix platform uses the same architecture (i.e. ControlNet) and a fiber-optic redundancy module in each controller chassis. By using either of these hardware platforms, you only write 1 program and load it into both cpu's. If a failure is detected in the on or primary cpu, control is "bumpless-transferred" to the back-up cpu.

[guillencito 0]

Is possible to do this kind of control using SLC's? Because now I have only SLC's in availability. And, in addition, if you have a program example for this control, I'll be thankful.

[mgvol 0]

I do not think you can do true redundant "Hot Back-up" with the SLC platform. I do not have a program example to show you, because the program code has nothing to do with the hot back-up arrangement. It is all set up in the hardware configuration (if PLC-5, this is the hot back-up module; in ControLogix it is the redundancy module). You write your control program as you normally would for your given process or machine. The redundancy functions run seamlessly in the background and if the primary CPU fails, you won't even know it has switched over to the stand-by CPU (unless you are monitoring this status bit in you ladder code). I would have been happy to show you an wxample anyway, but the last redundant system I did was about 4 yrs ago and I no longer work for that company.

[guillencito 0]

Thanks a lot! This info have been very helpful, mgvol. Best Regards!

[Eddie Willers 2]

The SLC-500 does offer a "redundant" I/O scanner module, the 1747-BSN. This gives two SLC-500 controllers the ability to work the way an old PLC-5 hot backup system did, because they will scan the same I/O. If both controllers keep the same program, then they can work as "backups" to one another. This is not as sophisticated as the ControlLogix system, where the two controllers are literally running in parallel and changes made to one are made to the other automatically. Because the uses of redundant controllers are as widely varied as the uses or ordinary controllers, I don't think you will find "examples" outside of the User Manuals.

[guillencito 0]

For programming examples I mean, whether in order to keep both PLC's working together, is necessary some special instructions, like MSG, to "exchange" data between both PLC's. Did you understand me? I thank for your answer, Eddie!

[mgvol 0]

Right you are Eddie...you can do redundancy w/the 1747-BSN! I was not familiar w/this product. Anyhoo, here's the manual for it containing config and programming examples. 1747_BSN.pdf