When testing large specimens such as motors, generators or the occasional GSU with the Doble M4000 M4100 Power Factor Insulation Analyzer, the Doble Type C 10kV Resonating Inductor provides the extra current needed to achieve high voltage test levels. The Doble Type C 10kV Resonating Inductor is tunable, allowing for precise balance with the test specimen.

The Doble Type C Resonating Inductor (i.e. Resonator) is an iron-core reactor with an adjustable air gap, capable of resonating capacitance of approximately 0.05 to 1.0 microfarads at 10 kV 60Hz (0.07 to 1.4 microfarads at 10kV 50 Hz).