Shadow function for protection monitoring systems

A diagnostic method, comprising:

• receiving, by selected ones of a plurality of processors, data acquired by a sensor;
• executing, by a first processor of the plurality of processors, a plurality of safety functions, wherein the executed safety function is configured to perform operations including:
• determining one or more sensor measurements representing an operating parameter of a monitored asset from the received data;
• comparing selected ones of the sensor measurements to respective predetermined alarm set points;
• and
• determining a safety function output for the selected sensor measurements based upon the sensor measurement comparison, the safety function output representing a first status estimate for the monitored asset;
• and
• transmitting, by the first processor, the safety function output;
• executing, by a second processor of the plurality of processors, a plurality of shadow functions during different respective portions of at least one diagnostic interval, each shadow function corresponding to a respective safety function and configured to:
• receive the same one or more sensor measurements received by its corresponding safety function;
• and
• determine a shadow function output for the corresponding safety function during its respective portion of the at least one diagnostic interval, wherein the shadow function output represents a second status estimate for the monitored asset and is configured to replicate the safety function output of the corresponding safety function when the safety function output and the shadow function output are free from error;
• and
• transmitting, by the second processor, the shadow function output for safety function output;
• receiving, by a third processor of the plurality of processors that is different from the first and second processors, the safety function output and the shadow function output;
• validating, by the third processor, each safety function output by comparing the safety function output with its corresponding shadow function output,
• outputting, by the third processor, a condition for the monitored asset based upon the validation comparison;
• receiving, by at least one relay, the output condition;
• and
• triggering actuation of a corresponding relay contact to transmit a corresponding signal for annunciation of the output condition.