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Strategic Proof Testing

Safety Instrumented Systems (SIS) are designed to provide automatic protection functions. A typical design includes a sensor to detect the potentially dangerous condition, a safety PLC and a remote actuated valve capable of taking action to prevent an accident.  In a well designed chemical plant the potentially dangerous conditions occur very infrequently.  Hence these equipment sets may be idle for long periods of time and operate only once every few years.  In such a situation failures of the equipment that prevent a safety response may go undetected for years without a periodic “proof test.”

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