I was reading a laboratory to study some backgrounds about common mode rejection (CMR), when I saw this image:

CMR measurement

Does the aluminum plate connected to ground under the multimeter increase the reading precision or does it do something else?

This is the laboratory report (Spanish).

  • 2
    \$\begingroup\$ "... In this case, a low-cost UNI-T multimeter was used. ..." That yellow meter looks like a DT830 -- that's about as low-cost as you can get! \$\endgroup\$
    – ErikR
    Nov 9, 2022 at 13:09

2 Answers 2


It's not to reduce any sort of interference, it's to introduce interference into the reading. The setup shown in figure 3 shows that they have the ground of the function generator connected to the aluminum plate and the output connected to one end of the resistor. Fig. 3b is the schematic representation with the parasitic capacitance between the circuitry of the multimeter and the plate. You can see where they sweep the frequency and observe the effect on the reading of the meter.


I would think that the plate is to provide a nice capacitive surface to couple noise into the meter and find out how much noise is coupling into it from RF sources.


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