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From: whit3rd on 23 Apr 2010 16:08
On Apr 23, 10:51 am, Kari Laine <klai...(a)gmail.com> wrote:

> I am testing several things and now I would need a
> very exact current and voltage source.
> It would be nice if it were correct to 0.001mV/mA.

One can purchase pre-trimmed reference voltage components,
like AD581, with various precisions ($5 to $40). Standard cells
(with a calibration certificate) are higher.

Nothing will get you to .001 mV unless your laboratory setup
includes VERY tight temperature controls; wiring thermocouple
effects make anything below .05 mV into a difficult exercise.

A calibrated voltage source, an attenuator (some of the old
potentiometers, available on the internet at bargain prices, will
hold four-digits of accuracy easily) and a few precision resistors
makes it possible to generate lots of voltages and currents
with simple operational amplifier circuits. Alas, you DO have
to know and treat all the important error sources to do this kind
of precision work.

Voltmeters in parallel have the same applied V; ammeters in serial
have the same applied I. Everything else, you gotta keep track of
errors and error propogation.
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