An Electric Field Meter with Extended Frequency Range

The frequency range of a field meter of the field mill type has been extended by applying a system of balanced modulation. This is achieved by incorporating two complementary sets of stators. The amplified signals from the stators are detected in a clamping circuit. In the instrument which is described, the frequency range extends to 22 kcps although the modulation frequency is 120 cps. The method by which the frequency range has been extended can be adapted to other instruments employing mechanical modulation.