We have the target board with three AD7687 ADC for phase-to-phase voltage measurement of three-phase system of alternating current.
The target board schema is shown figure 1.
MCU is the microprocessor control unit. MCU start the ADC conversion and read data and output data to DAC. DAC connect up the Lecroy's scope.
If voltage signals is small that measurement signals is good (figure 2).
If voltage signals is bigger that measurement signals defect (figure 3).