Internal Resistance Measurement
The electronic load is able to measure the internal DC resistance of the connected DUT.
The determination of the internal resistance is done in the way specified in several standards for batteries and accumulators, e.g. DIN EN 61951, DIN EN 61960:
The DUT’s terminal voltage is measured at two defined load levels lasting a defined duration.
At the end of the first load level I1 the voltage U1 is measured at the DUT. Then the second, higher load level I2 is immediately set. At the end of the duration of I2 the DUT’s voltage U2 is measured. Then the load calculates the internal resistance from the quotient of the differences of the measured voltages and currents:
Ri = (U1-U2)/(I2-I1)