I want learn how to view the CM and DM components of a signal on a usual two channel scope. The reason for this to be able to verify whether a noise superimposed on a signal is CM orDM.
Regarding my below drawing, I thought if I can measure Va and Vb with two seperate channels I might use the MATH function to see the CM and DM components. Imagine Test Device in the figure is a power supply with its plus and negative terminals shown and you observed noise/interference at some point by a scope.
And now you want to check whether what you have seen as noise is due to CM or DM interference.
Would the following setup work:
Where should be the probe ground leads be connected?
What would plot the CM and DM if MATH function is used? Would Ch1+Ch2 plot the common mode part of the signal?