Just saw this , and have seen you guyzz talking about uA & nA
http://alternatezone.com/electro...
This should be rather precise.
Wondered if it should have been in OffTopic , but it is electronics.
If someone in EU is making PCB's & getting comps , i'd like to be in.
Ohh .. he also have a resistor calc tool , that executes fine under wine :-)
http://www.eevblog.com/files/Res...
/Bingo
It would be interesting to hear how the device does over time and temp. I had a conversation a few weeks ago with the experts on the worlds best ultra resistors and they cautioned me about low valve resistors and how you get into pcb trace resistance issues, etc. The tempco of that milliohm current sense resistor and the copper pcb may change over time and temp. That may work against the very good autozero opamp the design uses;. Just something to watch out for.
executes fine under wine
Flukes solution is to use what is basically a precision current to voltage converter. With a virtual ground input, it has zero burden voltage at pico amps.
One more comment.. the Maxim opamp can only swing to within 10 to 50 millivolts of the rails depending on load from 10k to 1k.
@alwelch:
The OP does not even need to be rail-rail, it gets something like +-1.3 V supply.
I see two problems with this device: Overload protection is quite weak. So its relatively easy to break the µA range.
I doubt it will reach the quoted precission: With a cell phone somewhere in the room offets can be significant if no really good HF protection is present.
Even an chopper OP-Amp has an offset in the 0.1 µV range, which translates to 10 µV at the output - this is visible with most 4.5 Digit meters. Thermovoltages form the swithces are probably also a problem.
At least for small currents (e.g. less than 1 mA) a transconductance amplifier is a better solution, if one allows for lager batteries.
