Abstract: An industrial controller performance monitoring system includes a detector connected to a controller. The detector is optically coupled to an output, such as a display, of equipment under test and the controller is configured to receive a signal from the equipment under test that is indicative of an instruction to generate the signal monitored by the detector. A comparison of the detection of the signal with the instruction to generate the signal provides an indication of operation of the equipment under test without interfering with operation of the equipment under test.