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For a precision and simultaneous analog signal data acquisition; several force, temperature and acceleration transducer outputs are coupled to a daq board input channels through signal conditioning modules for each channel. These modules acts like differential inputs they have very high CMR, they provide ch-ch isolation and also provide built in anti-aliasing filters.

So far so good, but I still have AC line interference coupling through power supplies. And if I connect power supply DC ground terminal to earth terminal the interference disappears.

I tried to draw the scenario below where switches indicates connection option between the power supply DC ground and the earth. In the diagram two channels shown as example and in real there will be around 15 where cable lengths are around 12 meters:

enter image description here (Tr indicates a transducer)

Is there any issue with such a scheme for the above diagram? I know if there would be no isolation modules there would be ground loops but in this case there seems to be complete isolation but still I don’t have more experience beyond this argument for the overall system here.

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To further reduce the SMPS-injected trash, insert this between each SMPS and the other circuits

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Should C1, C2 and C3 polarized capacitors? Can they be electrolytic or should they be ceramic type? There is no ground plane in my case it is field wiring with cables. \$\endgroup\$
    – floppy380
    Apr 3, 2019 at 15:22
  • \$\begingroup\$ Since your circuit has voltages, use polarized caps. To have the caps perform well at high frequencies, use1" by 1/2" pieces of PCB where I indicated "ground planes". You want to minimize the ESL of the cap and its via to the "ground plane", for best attenuation. Do not use leaded capacitors. If necessary, use smaller values than 10uF, but use SMT. \$\endgroup\$
    – analogsystemsrf
    Apr 6, 2019 at 3:39

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