Measuring RC Time Constants on the Bench

Question

Do measured RC charge curves match theory once probe loading is accounted for - and how much does a 10 MΩ probe actually perturb a high-impedance RC?

Method

Charge a 1 µF film cap through 10 kΩ, 100 kΩ, and 1 MΩ resistors; capture the curve; fit τ; compare against nominal values and against values corrected for the probe’s 10 MΩ input resistance.

Results

At 10 kΩ the fit lands within 1.8% of nominal. At 1 MΩ the uncorrected error is 9.6% - and shrinks to 0.7% once the probe’s parallel resistance is included in the model.

Interpretation

Bench technique validated: the instrument chain is trustworthy once its own loading is modeled. That baseline makes later, subtler measurements defensible.