u1x2x1u1x2x1AdxControllerAdx_HighAdx_LowADxen05000296-2-en.vsdIEC05000296 V2 ENFigure 239: Simplified drawing of A/D converter for the IED.The technique to split the analog input signal into two A/D converters withdifferent amplification makes it possible to supervise the incoming signals undernormal conditions where the signals from the two converters should be identical.An alarm 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. This is done in a validation filter which has mainly two objects: First is thevalidation 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,that is the signal that has the most suitable level, the ADx_LO or the 16 timeshigherADx_HI.When the signal is within measurable limits on both channels, a direct comparisonof the two channels can be performed. If the validation fails, the CPU will beinformed and an alarm will be given.The ADx_Controller also supervise other parts of the A/D converter.16.2.5 Technical dataTable 404:Self supervision with internal event listData ValueRecording manner Continuous, event controlledList size 40 events, first in-first out1MRK 502 034-UEN - Section 16Basic IED functions487Technical Manual
