quadruple redundancy in Controllogix

[nileshsurya 0]

hi thr all plc ppl i have one question consider the following system configuration:- i have two separate controllogix hot redundant systems on a single controlnet network(say these systems are A and B). i also have about ten I/O racks on the same controlnet. five of these I/O racks are controlled by "A" and five of these I/O racks are Controlled by "B". now i want follwing to happen: when both A and B are healthy then the control should be normal as specified above. But when A fails(i'm talking that when both primary and redundant of "A" fail) then i want that the control of the I/O racks controlled by "A" should pass on to "B" and now B should be the owner of all the ten racks, it would be better if the same works for vice-versa conditions also. u can say tht im talking about quadruple redundancy (4-CPU's redundant to each other) i have one possible solution in mind,plz listen this and give me any valuable comments and suggestions. suppose i declare these I/O racks for multiple owners. now when both A and B are working healthily the output status of the outputs should be updated from A to B continuously over controlnet CIP messaging. now when the controller goes into fault i will write the fault handler in A to send a system faulted bit or value to the controller B. now based upon this bit/value the controller B now stops updating the output status by the data coming from(CIP messaging) A and it now actively controls the output status on its own by running the process logic which is in its own memory. is this possible to do. and if it is possible so how do we approach further.we can have a nice debate on this topic . Are there any shortcomings in this system. i want suggestions and comments from all u plc experts. eagerly waiting for comments. thanks in advance Regards Nilesh Suryarao AB PLC Programmer

[BobLfoot 302]

If I understand you correctly you have the following system. 1. Four ControlLogix Processors - Call them W,X,Y & Z 2. Ten I/O Racks connected by ControlNet - Call them 0 thru 9 3. Two ControlNet Coax Cables - Call them A & B Your Normal Setup is as follows: System 1 is Processors W & X using Cables A & B to Racks 0 thru 4 System 2 is Processors Y & Z using Cables A & B to Racks 5 thru 9 With the following Failures you want the following responses: If Processor W fails it is replaced by Processor X If Processor Y fails it is replaced by Processor Z If Processors W & X fail then the active processor Y or Z will pick up and control Racks 0 thru 4 If Processors Y & Z fail then the active processor W or X will pick up and control Racks 5 thru 9. The best scheme I can think of to achieve this is as follows. Set the W/X network up using Version 10 or later redundancy with an SRM Module. Also set the Y/Z network up using Version 10 or later redundancy with an SRM Module. For the System to System Rollover user Version 7.5 software redundancy which is implemented thru a switchover routine and SSV/GSV instructions to change rack ownership. Hope this helps.

[Contr_Conn 4]

I think Bob described system setup correctIy - at least how I understand it, except I thinks that all 10 remote racks are on the same controlnet wire. Next, no such thing as SRM Redundancy version 10, Only avaliable are: Ver 8, 11 and 13 available and 15 is coming Old "software redundancy" will not work with any newer versions and completely discontinued as unreliable solution. In any case changing ownership on-the-fly is very hard to do, and very close to impossible with controlnet, because controlnet uses strict schedule that can't be modified while in run time. Edited 23 Apr 2006 by Contr_Conn

[BobLfoot 302]

You are correct Redundancy is only in Versions 11,13 and 15 if you are talking post version 10 {Vesion 10 or later}. The old version 7.51 style of software switching redundancy is working quite effectively for a couple of large baggage handling and tracking systems and was running under version 11 just fine last time i checked. So to say it is obselete is premature at best. If Nilesh is to get his "Quad" redundancy he'll have to use SsV/GSV and software switching and find a way to live with the glitches that pop up. .

[Contr_Conn 4]

I can tell you that software switchover may be working in ver 11 but no longer supported by Rockwell, so Nilesh will be on his own Edited 22 Apr 2006 by Contr_Conn

[BobLfoot 302]

Nilesh - I posted a poll and topic on Redundancy some time back do you really expect two processors on the same system to fail at the same time. Your time and money would be better spent on redundant i/o than quad redundant cpu's.

[TimWilborne 108]

I believe BobLfoot is referring to THIS poll. And I think this is what I was referring in that poll as overkill. At what point do you need quadruple redundancy? Are we getting to the point that we have that little faith in our controls anymore? Is this going to a probe that is headed to Pluto? You want quadruple redundant processor then that is up to you, but can you explain to me why you would really need it?

[nileshsurya 0]

hello TWCONTROLS I need this system coz its the requirement from my client, he has said tht ABB System can offer him the same thing so i thought why couldnt AB CLX give him the same. this way the topic was raised. actually i dont know anything bout (OLD) software redundancy using SSV/GSV and software switching, can anybody point some examples or give more info bout the same. it will be very helpful regards NILESHSURYA AB PLC PROGRAMMER

[Contr_Conn 4]

Nilesh, I understand that you just trying to implement customer spec, but there is another thing called common sence. If customer did not trust to the pair of redundand processors without looking at redundand I/O, they really on the wrong path. I don't know what ABB offer, but I would bring this to your local RA guy and let him get advice from Redundancy Marketing in US. Software redundancy was introduced as temporary solution before SRM module was used in ver 8. It dos not provide bumpless transfer. It was completely discontinued few years ago as unreliable solution, I am not sure if any document left. Edited 23 Apr 2006 by Contr_Conn

[nileshsurya 0]

ya contr_conn, i understand tht this does nt make any sense but the client is demanding this as one of the requirement. he is asking tht it would be better if we provide this system.thts why i thought why not explore this possibility but i would still like to know more about software redundancy used earlier (just 4 info) .where do i approach?? regards NILESHSURYA AB PLC PROGRAMMER

[Contr_Conn 4]

Call your RA rep and ask him to contact Redundancy Marketing Manager in US

[BobLfoot 302]

Nilesh - some things to ask your client about his spec. 1. He has asked for quad redundant processors, but what about other more likely to fail items. a. Are the processors in different enclosures - Shame to lose all 4 processors to a fork lift. b. Is he getting Redundant AC Power from two different generating stations. Shame to lose the plant when a mongoose chases a snake into a transformer. c. Is the planning on Redundant DC Power supplies. Hate to lose a six figure process for a 39 cent fuse. d. Has he planned redundant process paths. Hate to lose that six figure process for a bad motor, belt, pipe or sensor.. You might also find this technote useful.

[Sleepy Wombat 27]

Mabey the client has been watching the TV series "LOST" where every 108 min a code has to input into a computer...Now since there was a plane crash there are a number of redundtant servers to hit the keystroke button required....

[BobLfoot 302]

Maybe just my humble opinion but most consultants writing specs for redundant systems are no better than the "snake oil elixir" salesman who promised my Grandfather a cure to all his ills. Redundancy is a cheap catch word for a usually shoddy attempt at control - reliable design. Give me a Control Reliable Fail Safe system with no critical single point of failure over a redundant system any day.

[TimWilborne 108]

Ok I am going to put my 2 cents in here and try to get out. And just so no one waste there time reading my post trying to learn about redundancy I for warn you, I can't help you with a redundant application ABB can offer a system with quadruple redundancy. For what? I have used ABB equipment before and there is no need for it to have this much redundancy. And I will definitely say the Controllogix need much less redundancy if it need redundancy at all. That would depend on the details of your application. And forget the SSV/GSV redundancy switching. They got rid of it because it was unreliable. Why would you put a system in place that was deemed unreliable on a redundant system?

[TimWilborne 108]

Thought about this a little more and I am thinking if you need that much redundancy shouldn't you be using different brands of processors? Say you have 4 Controllogix processors and there is a flaw in the firmware. They will all be susceptible to that flaw. Wouldn't it be better to have an AB processor and an ABB processor if it is that critical?

[nileshsurya 0]

hello thr all plc ppl well nothing is foolproof in this world if two processors can fail at same time then why not four plus there are some other issues also i would like to thank all you ppl for giving valuable comments to this post and help me(infact all viewing this post) in gaining knowledge hope this continues regards NILESHSURYA AB PLC PROGRAMMER