Kish -

Please forgive any offense by my shortening your name.

You might try a look at a web search using as keywords, "lockstep" and "rendevous" with the phrase "fault tolerant".

In the context of fault tolerant systems, lockstep means that operation of hardware and software occurs at regular, but not necessarily, periodic times. A comparison usually occurs at the end of a logical or numeric procedure. Rendevous means that comparisons across processors will be made within a specified range of time before moving to the next task. Rendevous permits multiple processes to use different processors or different algorithms to achieve a desired result, yet assure that each is continuing to operate as expected.

If only two processing paths are used and an impartial voter is used to determine the outcome, how would the voter decide which processing path is giving faulty information?

Another form of redundancy is analytical redundancy, wherein a model of the process is run. Outputs from two hardware control paths are consumed by the model, producing a total of three results from the systme. Two from sensors and effectors connected to the system, and a third from the model representing what sensors connected to the system should be (+/- tolerance).

Enjoy yourself,

Bruce