Quote:
Originally Posted by Superscope
Hi,
......so I need to be able to measure 37.5uA reasonably accurately.
Thanks
Ian
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Ian,
I gather from this remark that what you have is some circuit where you want the current to be exactly (or very close) 37.5uA when its properly calibrated. One thing that could help is to be able to generate 37.5uA to make your own calibration standard. This could be done easily with a precision 10V reference, many accurate to 0.003 % and some precision resistors 0.01% or better. Then your meter just requires resolution only and its calibration accuracy is not as important. Also if you have the reference you can be confident your work is accurate and not rely on some meter's calibration which could well be off.
Also, I'm not sure here what your test configuration is when you are measuring the 37.5uA, but it might be possible to use the 37.5uA current reference directly to perform the calibration task. One way to get around any series resistance in the circuit where the current is introduced ( I assume the meter movement ? and its resistance) is to set up a current mirror with a monolithic pair of matched transistors and use one arm for the generated current and the other arm for the meter movement. If this notion works then you would require no meter at all and it would be a cheap test jig to make.