two series resistors at the SMU main amplifier output

[Alex_Lelekov]

Сan anyone explain the function of two series resistors at the SMU main amplifier output?

(http://www.ni.com/white-paper/13093/en/)

[crossrulz]

If I had to take a guess, I would say it would be for accuracy at different ranges.  At smaller currents, you need a larger resistor in order to get the full voltage drop range of your ADC.  And larger currents, you need a smaller resistor to do the same.  So it probably just chooses which resistor(s) to read the drop from based on the range of the current output.

[Alex_Lelekov]

In this case, the parallel connection of resistors, not series, is much more logical to apply:

[ChrisR. · Accepted solution]

The picture is a block diagram, not a schematic.  The point is that there are multiple shunt resistors that can be selected.  Their exact configuration is irrelevant to the point of the white paper, and will of course be product-dependent.