I am confused about the input common mode voltage seen by an op amp configured as a differential amplifier for high side current sensing. Assuming that the op-amp and the load for sensing share the same ground reference (fig. 1), it is clear (i think) what the input common mode voltage is.
For the majority of op-amps this would violate the input common mode range given a 15V +Vcc. However, what if the op-amp is powered by a separate source (fig. 2) with a separate ground reference? In this case, I initially think that the op amp does not see the large input common mode voltage and instead only sees the potential difference across the shunt resistor. My reasoning is that the amplifier is floating and so from the amplifier's perspective Vcm=(0.1V)/2, but I am not sure if this is true. If not, how would the input common mode voltage be calculated here (fig 2)? I can't seem to wrap my head around this.