u1x2x1u1x2x1ADxControllerADx_HighADx_LowADxIEC05000296-3-en.vsdIEC05000296 V3 ENFigure 251: Simplified drawing of A/D converter for the IED.The technique to split the analog input signal into two A/D converter(s) with differentamplification makes it possible to supervise the A/D converters under normalconditions where the signals from the two A/D converters should be identical. Analarm is given if the signals are out of the boundaries. Another benefit is that itimproves the dynamic performance of the A/D conversion.The self-supervision of the A/D conversion is controlled by the ADx_Controllerfunction. One of the tasks for the controller is to perform a validation of the inputsignals. The ADx_Controller function is included in all IEDs equipped with an analoginput module. This is done in a validation filter which has mainly two objects: First isthe validation part that checks that the A/D conversion seems to work as expected.Secondly, the filter chooses which of the two signals that shall be sent to the CPU, thatis the signal that has the most suitable signal level, the ADx_LO or the 16 times higherADx_HI.When the signal is within measurable limits on both channels, a direct comparison ofthe two A/D converter channels can be performed. If the validation fails, the CPU willbe informed and an alarm will be given for A/D converter failure.The ADx_Controller also supervise other parts of the A/D converter.17.1.5 Technical dataTable 476:Self supervision with internal event listData ValueRecording manner Continuous, event controlledList size 40 events, first in-first out1MRK 504 135-UEN A Section 17Basic IED functions563Technical manual
