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Currently some transducer outputs through BNC connectors are directly coupled to a data acq. hardware's inputs.

I want to install low-pass filters right before the data acq. inputs and for the passive filter I want to use an interface as shown below:

enter image description here

Sometimes I see they use aluminium enclosures for such purposes.

My question is that, does it matter whether the enclosure is aluminum or plastic? Would the enclosure material have impact on 50Hz magnetic pickup?

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    \$\begingroup\$ What (potential) noise problem are you trying to cure and where does it come from? \$\endgroup\$
    – Andy aka
    Mar 7, 2018 at 15:06
  • \$\begingroup\$ It is just for anti aliasing. I will install an RC filter but for the enclosure material Im not sure. \$\endgroup\$
    – user1999
    Mar 7, 2018 at 15:09
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    \$\begingroup\$ So, is your "noise" problem one of too much signal bandwidth or is it too much external noise? There is a reason for my question. \$\endgroup\$
    – Andy aka
    Mar 7, 2018 at 15:10
  • \$\begingroup\$ too much external noise. \$\endgroup\$
    – user1999
    Sep 30, 2018 at 12:19
  • \$\begingroup\$ Is that noise in the bandwidth of the signal you want to keep? \$\endgroup\$
    – Andy aka
    Sep 30, 2018 at 14:56

1 Answer 1

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Non-magnetic metal enclosure dampens substantially 50Hz magn field only if it's several centimeters thick. Dampening happens via eddy currents. Soft iron (or even better high permeability mu-metal) helps if the thickness is one millimeter. High permeability closed case directs the low frequency magnetic field to pass the internal circuitry. Thick iron of course is better than thin. I have succesfully used 4mm iron case around an audio transformer near a power transformer.

You can also keep 50Hz magn field out of the signal by having no loops that generate voltage from it. If you have inductor, split it to 2 identical inductors which have opposite directions => catched sum voltage=0

If 50Hz is out of band, you can kill it by filtering.

A tight metal case is useful against high frequency noises.

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