Xenotime, Librarian of Æther 20h ago
Any electronics people know a simple/cheap circuit to precisely measure current but have the measured side be dc isolated (it’s biased at 30V)?

my naïve thought is to just have a good shunt into a like difference circuit with an op amp and resistors and then an ADC can read that

is there a better way to do this?

edit (clarification): some folks picked up on this but I need to measure pretty small currents (<100uA) sensitively so magnetic sensors probably are out. thanks for all the ideas!
Show threadMx. Chara Aznable (they/them) of Pnictogen
@xeno current sensing transformer?
Apr 4 at 5:02amWeb
Show threadXenotime, Librarian of Æther 8h ago
@mxchara that’s for AC currents I think?

I want to measure <100uA dc sorry
Show threadMx. Chara Aznable (they/them) of Pnictogen4h ago
@xeno there's a device called a zero-flux current sense transformer that can measure DC currents. here is one form of it: a Hall-effect sensor measures the magnetic flux induced in a toroidal core through which the current being sensed is passed, and that sensor is included in a feedback loop to generate a current IS which balances out the flux generated by the external current. A shunt resistor yields a proportional output voltage
Show threadXenotime, Librarian of Æther 3h ago
@mxchara oh yeah hall stuff can work, servoing a wire opposite is a pretty clever way to mirror currents across an isolation barrier honestly

I’d be worried about how possible this is at such low currents and the cost aspect but it’s really cool nonetheless
Show threadMx. Chara Aznable (they/them) of Pnictogen2h ago
@xeno now, what if you passed the current through a few loops of nichrome round a thermistor and passed a known and regulated current through another few loops of nichrome round a matched thermistor and gauged the current by the difference in temperature between the two thermistors
Show threadXenotime, Librarian of Æther 2h ago
@mxchara oh boy lol