i tried that. i connected ground of AD620 to one of the terminals of shunt but its not working. i am getting constant output 2.5Vrms irrespective of input.
How do you ensure that the resistor (input) terminals remain
between the instrumentation amplifier supplies, in your circuit?
You might make a "virtual input reference" by a resistor
divider from the two input terminals, high enough impedance
that it does not corrupt the measurement but low enough
that it can drag the (presumably isolated) amplifier rails to track
any reasonable common-mode impulse.