So, I found the old sketch, but it was realized with (pro Channel)2xM6225, Coto Wabash, OptoMOS copplers & pro current/voltage 2x good 1uF foil capacitors(switched charge memory) and OP07 for monitored voltages & a chopper amp_LTC1150_for 200uA/2mA current measuring.
Sensitivity switcher was per telecommand from a computer through a relay controlled...
The Detector current are sampled over a serial 1KOhm , filtered in both lines with two serial 10KOhms. & on the schema can you see the 100nF input capacitors to that filterings...
Through these switched capacitor sampling technique-you are polarity independent, you must only change the two input wires.
Todays opamps are really better, as the chopper amp so 20 years ago, but its function was not bad. The 6 channel meters are realized as a two sided PCB plug-in module. from 1mA it delivered 10V & from 100uA even 1V, has not the same output values on identical channels; depending from component tolerances, but with, for longtime, stabile deviances pro channel.
K.
Maxim & I think Burr Brown has good "Up-Side" current meter solutions, in remember all case for positive supply, but can not more tell whats the lowest measured current
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