# What can the source of 100Hz noise be?

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?

• A simple explanation could be that the noise comes from full-wave rectifiers, which create noise at twice the power line frequency, since separate diodes are used to conduct the positive and negative part of the wave. May 7, 2013 at 23:31
• thx, your answer makes really sense. but do you have any idea why there is a full wave rectifier needed in an industrial amplifier? May 7, 2013 at 23:46
• Probably the full wave rectifier is used in the power supply. May 7, 2013 at 23:56
• May be Flicker Noise.. Jul 18, 2013 at 12:35