Redundancy for OPC

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Redundancy in a process control system means that some or all of the system is duplicated, or redundant. The goal is to eliminate, as much as possible, any single point of failure. When a piece of equipment or a communication link goes down, a similar or identical component is ready to take over.

Early one morning, Mel Farnsworth was sitting in the control booth at the Hardy Automotive Parts assembly line, drinking his final cup of coffee before the end of the shift. Watching the line meter graph, he noticed that the yield and efficiency trends for the Line 3 had dropped to zero. He looked down through the control room window, but Line 3 seemed to be rolling right along. What was the problem?

The line was running smoothly, but Mel wasn't getting the data he needed. Somewhere between the PLCs and his HMI display there was a data disconnect. Maybe it was a fieldbus problem, or a bad network connection. Perhaps it was caused by his OPC server, or possibly even his HMI system. Whatever the reason, since Mel’s data connection was a single chain, one break in the chain means that he didn't get his data. To minimize this kind of risk and ensure the highest possible availability, mission‐critical systems often use redundancy.