Method and system for monitoring electrical isolation

A method for monitoring electrical isolation of a tested device by a test circuit, the method comprising:

• activating a first switch of a test circuit, a second switch of the test circuit, or both to provide an on state or an off state for each one of the switches for a plurality of time intervals;
• in a first state while the first switch is in the on state and the second switch is in the off state, during a separate time interval among the time intervals, measuring a primary voltage between a first terminal to electrical ground;
• in a second state while the second switch is the on state and the first switch is in the off state, during a discrete time interval of the time intervals, measuring a secondary voltage between a second terminal to the electrical ground;
• in a third state while the first switch and the second switch are in on states, during a compound time interval of the time intervals, measuring the primary voltage and the secondary voltage;
• in a fourth state while the first switch and the second switch are in off states, during a supplemental time interval of the time intervals, measuring the primary voltage and the secondary voltage;
• estimating an observed leakage resistance based on the measured primary voltages and secondary voltages of the first state and the second state;
• estimating a reference leakage resistance based on the measured primary voltages and secondary voltages of the third state;
• and
• determining that the test circuit has failed if the observed leakage resistance differs from the reference leakage resistance by more than a threshold amount, where the observed leakage resistance is based on voltage measurements during the separate and distinct time intervals and where the reference leakage resistance is based on voltage measurements during at least the compound time interval that does not temporally overlap with the separate and distinct time intervals.

A system for monitoring electrical isolation of a tested device by a test circuit, the method comprising:

• a first switch with its switched terminals coupled to electrical ground and a first resistor;
• a second switch with its switched terminals coupled to electrical ground a second resistor;
• a test driver for activating the first switch of a test circuit, the second switch of the test circuit, or both to provide an on state or an off state for each one of the switches for a plurality of time intervals in accordance with a first state, a second state, and a third state, where in a first state the first switch is in the on state and the second switch is in the off state, in the second state the second switch is the on state and the first switch is in the off state, in the third state the first switch is in the on state and the second switch is in the on state;
• a first voltage sensor for measuring a primary voltage between a first terminal to electrical ground during the first state, the second state and the third state;
• a second voltage sensor for measuring a secondary voltage between a second terminal to the electrical ground during the first state, the second state and third state;
• an electronic data processor adapted to:
• estimate an observed leakage resistance based on the measured primary voltages and secondary voltages of the first state and the second state;
• estimate a reference leakage resistance based on the measured primary voltages and the measured secondary voltages of the third state;
• and
• determine that the test circuit has failed if the observed leakage resistance differs from the reference leakage resistance by more than a threshold amount, where the observed leakage resistance is based on voltage measurements during different time intervals, among the time intervals, that are separate, distinct and do not overlap temporally.