Control System Redundancy

We are in the process of bidding on a project where the customer has specified a redundant control system. I know this is not much to go on and I hope to get some clarification as to the scope of what they want. All I know at this point is that they will be bringing 2 power feeds to the building and some equipment, such as pumps, will be fed from the two sources. We build water purification systems so mostly what my PLCs do are to control pumps and valves and a lot of monitoring,ie, flows, pressures, tank levels, various water quality measurements. I am mainly concerned about how to design a redundant PLC based system. We mostly use SLC 500 based systems or Micrologix. I have heard of hot back-up systems but have never installed one. We will be using AB so another PLC vendor is not an option. Anyone here have any experience with this?

Well if you want to stick with an SLC platfor you are going to have to build a redundant system yourself. Unless they have come out with one I haven't heard of. If you truly want a redundant system in the AB relm then the controllogix is the way to go. Very simple. No additional programming required for redundancy. Just a check box.

Well I did find a module that works with SLC that provides some redundancy. It's a 1747-BSN. Seems to do something similiar to the ControlLogix version though probably more limited.

Quantum Hot Standby will provide you with "more than 20 years redundancy" experience.

If the process genuinely requires redundancy then a redundant ControlLogix system is the best way to go.

Right now I am halfway through implementing a large and complex pumping station with a pair of 1756-L61 CPU's, redundant ControlNet and 12 off 480 Amp SMC-Flex softstarters, with 2 off 540 Amp PowerFlex VSD's.

The redundancy part of the project has been absolutely easy, just tick a box in the CPU properties and it all works. There are some design considerations and I suggest looking up the RA Knowledgebase for the relevant white papers and tech notes, but in practice if you design the system correctly it is easy.

I have attached a zip version of a relevant document.

The SLC version can be done but I have never used it and I would expect it to be much less flexible.

I agree - the ControlLogix redundant system is by far superior to the SLC or PLC5 backup systems. One huge difference is that either of the ControlLogix processors can be primary and switch back and forth. The PLC5 or SLC are dedicated. If you fail to the secondary (secondary now primary) and there is another failure, it won't switch back to the real primary.

While not a big AB fan, I think the ControLogix is the way to go.

Have your local (okay, regional) AB guy come in, along with your local supplier/rep. Be sure to get a good lunch out of the deal.

They should be able to deluge you with litterature and a good explanation. Hopefully, enough extra info that you won't have to bring in the big guns to help get it running.

regards.....casey

You might consider taking a look at Honeywell's hybrid controller, the HC-900.

I've used it for analog PID process control or front end data acquisition for which it is great.

They offer controller/power supply redundancy which our sslesman said is $10K over the price of the standard single controller/power supply.

And according to him, there's nothing to different from programming redundant hardware vs non-redundant.

I seem to recall that it includes some sort of pump transfer or pump staging algorithms, along with your typical sequencer. but since I don't do that I'm not sure of the particulars.

The price is what attracted me.

Their web page for it is at
http://content.honeywell.com/imc/pi/hybrid/hc900.stm
but I found the salesman much more informative than the web page.

There is a link on the right for their redundancy manual.

Dan

You definately should look at ControlLogix Redundancy setup.
With true bumpless switchover both ways this is the easiest system to implement.

You might not need to spend the big bucks....

The SLC-500 solution might be fine for your needs. So long as the ladder logic won't change, the I/O information will transfer to the backup CPU in the event of a main CPU failure.

ControlLogix/ProcessLogix is very high-end and costs it too!