Hi,

Our next project is in the tyre industry and our client insists on a redundant PLC system. Can you please specify the details regarding the redundant PLCs available in the market and also about your experience working on that?

 

Redundant means you require two CPUs with distributed I/O module systems. Try Siemens S7 400. If you require detailed, practical exposure, write to pune @ prolifictraining. com

 

Dear Pramod,

I would suggest you to go for redundant controllers in Hot Standby configuration where both the controllers are reading inputs and processing it at the same time, however only one shall write the outputs. Hot Standby controllers increase reliability tremendously. Both controllers are in close synchronization with each other and checking each other in each cycle. The transfer of control on outputs is bumpless and no loss of functionality occurs. Controllers may be hot swappable and swapped controller should automatically get updated. You may also look for controllers to be directly linked to each other without any interfacing device to avoid "Common cause of failure". Almost all reputed players in automation market are providing such controllers.

Regards,

C. Potdar

 

It would help to know why your client insists on redundancy. There's some specific reasoning that should be addressed.

The easiest redundant system I've worked with for critical process control (primarily temperture) is Honeywell's hybrid controller. Just use duplicate controllers, duplicate power supplies, the rack that holds them and the switchover module. Communications can be redundant if you want. No programming changes, no calculations for scan time changes, same programming for redundancy as not.

As a hybrid it won't do fast sequencing like a PLC, but it handles moderate speed discrete I/O adequately.

Bud

 

Yes, the Siemens S7-400H series is the high-availability redundant system. They have 3 ranges to choose from, the entry level is the 412H which is quite affordable (from a redundant controller standpoint). They use real-time synchronization with failover times < 100ms. The program and data is automatically sync’d, no special programming required for redundancy, everything is handled in the background. The redundant controllers can even be placed up to 10km apart from each other.

It supports redundant high speed communications all the way down to the I/O point. You can go nuts with the level of redundancy with 2 comms/remote I/O and then splitting I/O signals into 2 separate modules on 2 separate racks with 2 separate communication links all handled in the background. The system is also supports channel granular passivity, so even if one channel fails on a module the rest of the channels will continue to function and the failed signal will be switched to the redundant channel (usually on a different module).

http://www2.sea.siemens.com/Product...le-Controllers/Redundant+PLC/?languagecode=en

 

I think Bud made a good point.

Does the client have safety in mind or reliability? Depending on the answer that may exclude or include some vendors.

Also what level of redundancy? Redundant CPUs, and networks and I/O? What failover time is required if you adopt the hot standby approach? etc.

 

Be advised that there are other solutions that will set you free from HW vendors, several SOFT-PLC solutions can be chosen. Therefore you can use COTS hardware even in redundant setups. (Soft-PLC if you are required to supply a PLC solution).

Other software platforms will add hot redundancy without much programming effort, such as CDP from our company. (See http://www.icd.no)