The following sequence of events occurs to measure the Ru of the cell:
- The selected voltage is applied to the cell.
- A controlled potential EIS measurement is made at a 7 mV rms applied amplitude and a 100 kHz frequency.
- The phase-angle and real portion of the impedance are recorded.
- The frequency is successively decreased to 500, 200, 10, 5, 2, 1, 0.5 kHz. An EIS measurement is made at each frequency.
- If the phase-angle is less than ±7.5° at the frequency in use, the "real" impedance is reported on the computer screen as the Ru estimate.
- If the phase-angle is more than 7.5°, the phase-angle between the last two EIS measurements is compared.If the phase-angle diverges from zero at lower frequency, the real impedance at the higher frequency is reported as Ru and the user is warned that the Ru determination may be in error.