DC accuracy in mA range

[patzf]

Maybe I am overlooking something here, but you use a 10mOhm resistor as shunt for the mA range. The slide switch has (according to the datasheet) <20m Ohms.
You specify an accuracy of 0.1% in the mA range. How should that work if the "reference" resistor is in series with the switch? Even for 10m Ohms for the switch, the error is huge?

[vanthome]

Hi, sorry for my late reply. This is a very good question and yes, the "accuracy" as stated on the product page is 1:1 the tolerance of the corresponding shunt resistors. And then -- at least in the mA range -- it cannot be correct considering the contact resistance of the switch as per data sheet.
But I just did a reference measurement measurement for the nA range as described here:
https://github.com/nfhw/tinycurrent/blob/master/test_procedure.md

• I measured with only the slide switch in nA range
• I have bridged the connections that are connected through by the slide switch with a solder bridge

I took 3 pictures correspondingly and checked them in here:
https://github.com/nfhw/tinycurrent/tree/master/Scope_Shots

As you can see there is virtually no difference, the variance of the measurement over time is much bigger than the difference.
That means that the contact resistance has only a negligible impact probably because it's smaller than given in the data sheet.

Also the reference measurement described here
https://github.com/nfhw/tinycurrent/blob/master/test_procedure.md
Could not be so good, if the contact resistance would be as given in the data sheet.