This is a conceptual question about long analog signal transmission exposed to capacitive coupling and EMI noise as shown in below figures:
In Figure1 the input impedance of the differential amplifier/instrumentation amplifier is 100Meg Ohm. And in Figure2 the input impedance of the differential amplifier/instrumentation amplifier is reduced to 100k Ohm by adding it as shunt.
I can say that since the source resistance is 1k, in Figure2 the DC error is larger which can be calibrated out as well.
But I'm wondering the what happens to the effect of the capacitance coupling(like 50Hz power supply leakage) and common mode EMI(coupling to the cable wires) when we insert that 100k shunt resistor as in Figure2. If we decrease the input resistance by adding that 100k the amount of current looping is increasing. Does that affect the SNR or provide better noise immunity for EMI or capacitive coupling?