Working principle of internal resistance tester

The working principle of an internal resistance tester is usually based on the following methods:
1. DC discharge method: By discharging or charging a battery or capacitor for a short period of time and measuring the changes in voltage and current, the internal resistance is calculated according to Ohm's law.
2. AC disturbance method: Apply an AC disturbance signal of known frequency and amplitude to the battery, and calculate the internal resistance by measuring the phase difference between voltage and current.
3. Time constant method: measures the time required for the voltage of a battery to drop to a certain percentage at a specific current, and calculates the internal resistance using the relationship between the time constant, battery capacitance, and internal resistance.
4. Resonance method: Using an LC resonant circuit, measure the resonant damping of the battery at the resonant frequency to obtain the internal resistance value.
5. Four wire method: By using four test lines (two for current and two for voltage measurement), the influence of test line resistance on measurement results is reduced.