I'm making data acquisition with an amplifier (amplifier is amplifying a transducer and is connected to a data acquisition hardware).
After I make data aq. I am plotting the output signal data in fast Fourier transform. It is a DC output from the amplifier. I observed a sinusoidal ripple over DC voltage on an oscilloscope and I thought it was 50Hz.(Because we use 50Hz in Europe for power supply)
But when I take the Fourier transform the highest noise spike is 100Hz not 50Hz. 50Hz is the second after 100Hz in freq-power spectrum. And the other spikes are 150 and 200. The thing is it looks like harmonics of 50Hz but then why 50hz is not the maximum and 100Hz instead?