Regarding my previous question, an unbalanced(single-ended) source Vs is connected to inputs of an instrumentation amplifier and ground as follows:
I have seen above connection in many texts.
For simplicity let's assume Vs is DC and common mode voltage Vcm is DC. And all impedances are real and they are resistances.
And regarding the above diagram, let's say the line resistances Rl1=Rl2=100 Ohm. The input impedance of the inAMp is Rx=10 MegOhm. And the source impedance is 200 Ohm.
What I understand is the common mode current Ic1 loops through the following resistances:
and Ic2 loops through the following resistances:
If I'm not wrong the impedance seen from the hot terminal is: Rs+Rl1+Rx and the impedance seen from the negative terminal is Rl2+Rx.
My two questions are:
1-) It seems like Rx>>>Rs in an inAmp because of its buffers, does that mean the source impedance matching is less important than in a difference amplifier? Can Rs in practice can be neglected when using an inAmp this way? Let's say Rs is 50 Ohm and Rx=10Meg, would you still add a series 50 Ohm resistor to the negative terminal? Or would you neglect it because Rx dominates?
2-) Look at the third wire at the bottom from the negative terminal of the source to the ground of the inAmp. There is no resistor on that wire. In practice should there be a resistor there not to cause a short circuit?