This circuit produces an output current, Io, that is proportional to the input voltage, Vs. The output current is measured using a ammeter. The input voltage is the voltage of the voltage source. The constant of proportionality is equivalent resistance of the series resistors. The value of the equivalent resistance is determined by the resistances, R1 and R2, of the two resistors that comprise the series resistors.
The equivalent resistance, Req, of the series resistors is given by
The output current is related to the input voltage by
The design equations
show how to select values of R1 and R2 to achieve a specified value of equivalent resistance.