Xenotime, Librarian of Æther 
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!
2:02amWeb
Show threadXenotime, Librarian of Æther 12h ago
#electronics ig
Show threadmx alex tax1a - 2020 (6)10h ago
@xeno seems like a job for a wheatstone bridge
Show threadToroidalCore11h ago

@xeno Assuming hall effect sensor isn't what you're looking for, there are special current sense amplifiers meant for high-side shunts that can tolerate higher common mode voltages. Here are a couple:

https://www.ti.com/lit/ds/symlink/ina190.pdf
https://www.ti.com/lit/ds/symlink/amc1301.pdf

Another option is to float an ADC and normal op amp, and then supply it with isolated power from a flyback converter, and use a digital isolator to talk to the ADC.

Show threadRay Kelm10h ago
@toroidalcore @xeno I've done something similar to the second idea using a small dc-dc converter.
Show threadToroidalCore9h ago
@rayk @xeno At a previous job we basically did that for measuring high side battery current in a BMS. It's more complicated, but it does work.
Show threadXenotime, Librarian of Æther 15m ago
@toroidalcore oh this isolation amplifiers could be great options thanks!
Show threadvxo10h ago
@xeno
Isolation amplifier might be what you want.
Show threadXenotime, Librarian of Æther 20m ago
@vxo ooh this seems very much like what I want :3
Show threadMx. Chara Aznable (they/them) of Pnictogen9h ago
@xeno current sensing transformer?
Show threadXenotime, Librarian of Æther 19m ago
@mxchara that’s for AC currents I think?

I want to measure <100uA dc sorry
Show threadlumiya8h ago

@xeno
Another option that might be interesting would be magnetic based sensors.

This article is designed to sell you those. But could be a start. (Other manufacturers exist this was just the first link I found)
https://www.allegromicro.com/en/insights-and-innovations/technical-documents/next-generation-current-measurement

One big drawback is that strong external magnetic fields do influence the result.

Those as well as the shunt based sensors do have fully integrated options. As well as some with an integrated ADC and digital interface.

Next-Generation Current Measurement - Technical Article | Allegro MicroSystems

Introducing the Next-Generation Current Measurement Series: Advanced magnetic current sensors accurately detect magnetic fields generated by current flow, offering precise current level measurements.

Show threadHendi4h ago
@xeno I've got a bunch of 100 khz bandwidth isolated current sensors by VAC Vakuumschmelze, measure side is 5 V, the current path is well isolated and can be wired for about 50, 25 or 13 A.