two general observations 1) the differences in the RMS value an the highest magnitude in the FFT may be due to scaling, 0 to peak vs RMS in the FFT
2) the cycle average VI is a good one to use, however the default percentage of full scale numbers are very tight. These determine how many true cycles you have in your data, and may be filtering out cycles, giving you the waveform size of 0. Try lowering the limits to 70 for the high side, and 30 for the low side, rather than 90 and 10 which are the defaults. What are you trying to learn from the AC voltage? Are you performing some sort of power quality test? Hope this helps, Preston Johnson
