I have been designing my own LCR meter that uses the V-I method to make measurements. I have finished the sine wave generator and processor side, but I got stuck at the sensing part.
Here I have 3 types of sensing circuits:
simulate this circuit – Schematic created using CircuitLab
The first one senses the current on the high side and measures the voltage on DUT on the low side. The next one is the opposite of the first one: DUT is on the high side and current sensing is on the low side.
The last one senses the current on the low side too, but with a transimpedance amplifier (I don't know if it can be moved to the high side).
Every one of them seems to have different pros and cons, and sometimes one says it is a pro whereas the other says it is a con (and vice-versa). This confused me much more.
I have made some tests and every one of them gives "slightly" different results on the same DUT values (approx. -/+30 nF on a 100 nF ceramic capacitor and -/+50 μH on a 100 μH inductor), and since they aren't precise/have high tolerances, my confusion still exists.
Which is the correct way to obtain accurate results? Also, can a 100 mV sine wave test signal be used to measure components in-circuit? Or should I stick to a 1 V signal and measure components individually?
It doesn't need to have lab-standard precision since I make the entire circuit from recycled components. I only want to measure things better than a multimeter with extra details.
