A Six Decade Linear Response Digitized Electrometer

The design of a wide range digitized electrometer with an operating range from 10-12 to 10-6 ampere is described. A linear tire-base output within ± 1% of a decade over a 6-decade operating range has been realized. The design utilized the input current to charge a small capacitor as the time element. As the capacitor is charged to a predetermined threshold voltage, it causes an astable mrultivibrator to free-run for one cycle, producing an output pulse. The charging capacitor is then immediately reset and reactivated for the next cycle.