I'm trying to build a high-side current sensing circuit with a differential op-amp which can be seen below:
The LT1006 is actually an LM358 IRL(I know it's a peanut op-amp, but it's what I have available). Anyways, according to this setup, I should have unity gain. 5V/101.1 OHM = 49.4mA. So the shunt has 49.4mA * 1.1 OHM = 54mV across it, and therefore the LM358 should output around the same voltage, but it doesn't. I've made sure the resistors are very matched and also tried using 100k resistors. I've also experimented with different power rail voltages and even tried setups that would give a gain of 5, 10, and 20, and I still can't get the op-amp to output the expected voltage. What am I doing wrong? I've read the datasheet and I'm pretty sure I am within spec of the common mode input range.