A multichannel electrometer voltmeter that employs a mechanical resonator maintained in sustained amplitude-stabilized oscillation has been developed for the space-based measurement of an Internal Electrostatic Discharge Monitor (IESDM) sensor. The IESDM is new sensor technology targeted for integration into a Space Environmental Monitor (SEM) subsystem used for the characterization and monitoring of deep dielectric charging on spacecraft. Creating a stable oscillator from the mechanical resonator was achieved by employing magnetic induction for sensing the resonator’s velocity, and forcing a current through a coil embedded in the resonator to produce a Lorentz actuation force that overcomes the resonator’s dissipative losses. Control electronics employing an AGC loop provide conditions for stabilized, constant amplitude harmonic oscillation.

The prototype resonator was composed of insulating FR4 printed-wire-board (PWB) material containing a flat, embedded, rectangular coil connected through flexure springs to a base PWB, and immersed in a magnetic field having two regions of opposite field direction generated by four neodymium block magnets. In addition to maintaining the mechanical movement needed for the electrometer’s capacitor-probe transducer, this oscillator provides a reference signal for synchronous detection of the capacitor probe’s output signal current so drift of oscillation frequency due to environmental effects is inconsequential.

This work was done by Brent R. Blaes and Rembrandt T. Schaefer of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47336


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Amplitude-Stabilized Oscillator for a Capacitance- Probe Electrometer

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This article first appeared in the May, 2012 issue of NASA Tech Briefs Magazine.

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