This weekend, under pressure to get some results, I needed to measure current in a feedback path--a relatively low current--microamps. In this application, I could afford to put a series resistor (suffer the burden voltage that resulted) to get something to measure with my scope using two probes and taking the difference (CH1-CH2). However, there was just not enough sensitivity for a good reading.
Some time back, I made an EKG amplifier using an AD624, so I thought, hey why not? I got it out of the "project" bin, modified the gain to 100 and used it to make the measurement. Fortunately, at a gain of 100, the BW was sufficient, and there were no common-mode issues to contend with when powered with +/-15V.
It worked. I used a 1k resistor, which seems big, but for this application, not an issue.
Showing the schematic is a bit laughable because the AD624 requires almost no external components but here it is anyway.