Planning redundant communication network

Hello to all,
There are few investments on the way soon. I need to do planning of cost effective but reliable solution. I need to have redundancy implemented. Basically there is a need to have reliable communication between PLC CPU and distributed I/O stations. One solution is to use two redundant CPs on both PLC side and distributed I/O side and to have classical profibus or ethernet bus. Second solution would be to use ethernet and profibus ring.
Now I have the following questions open:

1. Is first solution really a redundant one regarding communication?
My answer is no! Redundant communication will not provide a redundant communication solution. Of course, if one CP fails, communication will carry on using second CP.

2. If one node on profibus/ethernet bus fails there is a possibility to turn down other network components?
I'm not sure about this one. I don't believe that failure of one component can generate disturbance to others. Can you clarify this one? What are your experiences?

3. Second solution with ethernet/profibus ring will provide true communication redundancy?
I think yes if managed switch is used. In case of wire break there is alternative communication path between any two components. This would be truly single fault tolerant solution.

Please, share your experience. I need to have optimum balance between cost and availability. Goal is to have a true single fault tolerant (any component including wire break).

Cheers!

I just completed the design of a redundant system for a municipal water treatment facility in Florida. I am using S7-400H redundant processors (true failover redundancy cannot be done with the S7-300 CPUs). I designed a Profibus fiber-ring with redundant fiber pairs (one for each processor - required architecture by Siemens). I used ET-200M I/O modules with redundant comms. Here is my take on your three questions/issues...

1)Redundant CPUs are key - depending on your choice of manufacturer, the required network architecture could vary. I always try to install or have a fiber ring available, if the budget allows.

2)A node failure on Profibus shouldn't affect other nodes.

3)Yes, fiber ring. Switches are not needed for profibus fiber-ring. Use OLM modules (fiber to DP).

Thank you cbattles,
yes, I was thinking about redundant CPUs also, but not really sure if that is going to fit my budget. I think it's more likely to fail component of cable.
Network switches are not needed for profibus, but they are mandatory for ethernet rings because of TCP/IP communication and avoiding circular data frames, right?
It seems that S7-400H system with ET200M (with S7-300 modules) became standard solution for complete redundant systems.

Yes, putting your ethernet switches on a fiber-ring is also recommended, but make sure your using a different pair of fibers than that of your PLC communication.

The need/use of Redundant CPUs really depends on the installation and if the facility has adequate staff (both in number and intelligence). If there is always a technician on-site that can respond quickly to minimize downtime, then maybe CPU redundancy isn't required.

Pandiani and cbattles,
We have completed about 20 redundant systems in the past couple of years and found that the redundant S7-400 H is one of the best solutions if you can afford it. We have also used the software redundant solution and for non critical processes that are not fast and can stand a bump in the transfer. S7400 H's require specific IM153 and the Siemens active backplane bus and special mounting rails also for these bus components.

My suggestion would be to separate the remote rack communications and make them a single line lan. If you lose one of them you still have the other for backup and the ring just costs you extra money.

If you want to do this the way you have it posted and save bucks try the Vipa solution with their redundant IM253 Profibus comm cards. It still programs with Step7 and will possibly be half the cost.

Here is a link to the manuals if your are interested.

ftp://www.mcaps-inc.com/1VIPA%20Manuals/200%20system/Vipa%20Redundancy/

Hello,

I've got proposal that is attached in this post. It uses Profibus with OLM (optical link module). It seems that this is also a form of ring, but even more advanced. This is similar with double ring, but this solution is not double fault tolerant if both links from OLMs to CPs in central rack fail.
On the other hand, there is double fault tolerance in communication between distributed I/Os.
Is this configuration has some specific name?

Thanks

Paneiani,
I do not think this configuration for redundant communications to Siemens remote I/O to a single processor is supported in the hardware configuration in Step7. I believe that you will have to do extensive programming to operate a system like this because the IM's in a redundant configuration with redundant CPU's have the same profibus address if they are in the same rack. In this case the addresses will be different. Have you done a hardware configuration to see how this would be configured in Step7 yet.

Also the OLM's, the way you have them setup, are simply putting the remote I/O networks in a star configuration and not in a ring configuration. There are some much less expensive products to do this. OLM' were designed for fiber optic communication networks for noisy electrical environments or for long distance communications, or for fiberoptic rings, or for fiber optic redundant rings.

If you will decide what you want to do and how you want to do it i will halp you put a system together that will work for you.

Thank you gkelly,

I'm actually needs to decide what is the best for our budget, so I can write specification. I'm not system integrator but maintenance engineer. I'm helping my colleagues to decide what system they need and want.
I'll suggest them to try to ensure enough means to have redundant ethernet communication with S7-400H redundant system with PCS7. I've read some manuals and there are a lot of good informations about S7-400H system with redundant communication ring as you suggested.
Thanks for the help.