I have a material and I want to measure the voltage and current through it over time. Unfortunately I only have an automatic voltmeter and the resistance of the material changes over time. Because I can't measure the current and I don't know the resistance I created a circuit to measure this. See image below.
R1 is the material with variable resistance (disregard the 2kO). I choose a known resistor (R2) and measure the voltage through that. I also know the applied voltage. This way I can figure out R1 as well as the current through the circuit.
The current is I = V2 / R2
The voltage is V1 = Vtot - V2
The resistance is R1 = (Vtot/V2 - 1)*R2 or R1 = V1 / I
My question: will this work? I did the math and it should, however, I have done some tests and it is not working as expected. Should R2 be a value close to R1? Will the voltmeter affect the current path and create a parallel circuit? I need to know the stuff that someone who has some experience with circuits would know.