Patent ID: 8466691

Claim:
A method for determining an insulation resistance of an electric DC circuit having at least a first terminal and a second terminal, the method comprising: (a) performing a measurement cycle comprising: measuring at least one first terminal voltage sample between the first terminal and a reference potential and at least one first high voltage sample between the first terminal and the second terminal; measuring at least one second terminal voltage sample between the second terminal and the reference potential and at least one second high voltage sample between the first terminal and the second terminal; and measuring samples of the current drawn between the first terminal and the second terminal, the current samples being taken at least immediately before and after the voltage samples of the measurement cycle are taken; (b) verifying that the change of the measured current does not exceed a predetermined change rate, using the current samples; (c) calculating a total insulation resistance from the first and second terminal voltage samples and the first and second high voltage samples of the measurement cycle and from resistance values of a measurement circuit; and (d) calculating a first insulation resistance between the first terminal and the reference potential and a second insulation resistance between the second terminal and the reference potential, each of the first and second insulation resistances being calculated from the total insulation resistance, the first and second terminal voltage samples and the first and second high voltage samples of the measurement cycle and from resistance values of the measurement circuit.