Building a DIY nano ampere current meter

[fracton]

We recently had an issue with a 6 1/2 digit digital multimeter from Keitheley at work. As it still seems to be under warranty we had to send it back to the vendor for repair. However, that got me thinking about a DIY current meter that can measure 10 - 1000 nA level currents.

I am thinking about using the following for build my nanoamp meter:
- OPAMP: an LMC6082 or LMC662,
- MCU: arduino uno + ADS1115 for a 16bit ADC or a raspberry pico pi (2040)
- LCD screen to put together the ourput

Also, see this thread that I posted on the metrology board.

[Terry Bites]

A simple transimpedance amp might suffice but It'll be hard to build one with the same spec as the Kiethley. Watch out for stray capacitance at the input!

If you're working with DC amps and not in a hurry for your reading, use an integrator circuit. integrate, hold, measure and reset. Decent caps are so much cheaper than very high value resistors. Integrators are inherently stable unlike TIAs.

Also see the discussion on kelvin switching for TIAs. At low currents reed relays are a must.
https://www.analog.com/en/resources/analog-dialogue/articles/programmable-gain-transimpedance-amplifiers.html

[Gyro]

Note that this is effectively a [EDIT: partial] double post of a thread in the Metrology section (as the OP referenced), that is getting a reasonable number of replies... https://www.eevblog.com/forum/metrology/diy-nano-ampere-current-meter/

@OP: Please don't do this - it leads to duplication and waste of time and effort, as seen above. It won't win you friends.