What type of circuit is typically used for testing high resistance?

The correct answer is a megohmmeter circuit. This type of circuit is specifically designed to measure high resistance values, typically in the megohm range, which is crucial for assessing insulation resistance in electrical systems. Megohmmeters apply a high voltage to the resistance being tested, which allows for precise measurement of insulation integrity by determining how much current leaks through the insulation.

Megohmeters are particularly valuable in diagnosing potential issues with insulation breakdown or degradation, which can lead to equipment failure or safety hazards. They can also help identify the condition of wiring and components in aircraft, ensuring safety and reliability in operations.

In contrast, while a low voltage AC circuit and a DC circuit at high frequency could involve resistance measurements, they are not ideally suited for testing high resistance values. A series resistance circuit, on the other hand, is a basic concept used in various applications but lacks the specialized capabilities needed for high resistance testing like those found in a megohmmeter circuit.