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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?

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    \$\begingroup\$ 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. \$\endgroup\$ – AndrejaKo May 7 '13 at 23:31
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    \$\begingroup\$ thx, your answer makes really sense. but do you have any idea why there is a full wave rectifier needed in an industrial amplifier? \$\endgroup\$ – user16307 May 7 '13 at 23:46
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    \$\begingroup\$ Probably the full wave rectifier is used in the power supply. \$\endgroup\$ – Renan May 7 '13 at 23:56
  • \$\begingroup\$ May be Flicker Noise.. \$\endgroup\$ – Enthusiast Jul 18 '13 at 12:35
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user16307 asks: "but do you have any idea why there is a full wave rectifier needed in an industrial amplifier?"

Have you researched full-wave versus half-wave rectification?

Half-wave rectifier raw output:

enter image description here

Full-wave rectifier raw output:

enter image description here

From these images, it is clear that the output of the full-wave rectifier reduces the energy storage requirements of the power supply filtering circuit.

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  • \$\begingroup\$ i got your point. makes really sense now. \$\endgroup\$ – user16307 May 8 '13 at 16:24

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