An Electrometer for Use in Scientific Space Instruments

A wide-range vibrating-reed electrometer that obtained extensive detailed data on the "solar wind" during the Mariner II flight to Venus is described. This circuit used an inverting carrier-type dc amplifier with a logarithmic diode as its principal feedback element and represented the first successful application of a space-qualified dynamic capacitor electrometer. This system also represents one of the earliest all-semiconductor amplifiers to be used in a dynamic capacitor electrometer. The wide dynamic range of the application (10-13 to 10-6 A) required the stabilization of a closed loop having 7 decades of continuous variation in the dynamic resistance of the primary feedback element. Some details of design, analysis, and performance associated with the electrometer amplifier and its feedback system are presented.