A Digitizing Electrometer System Using an Integrating Circuit Preamplifier

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Abstract
An electrometer system is described which makes use of a conversion from input current to frequency. The data handling section employs digital circuit techniques which allow the dynamic range of the system to be adjusted to the requirement of the experiment, and which present the output in pulse form compatible with contemporary logic systems. The conversion of the input current variable to frequency is achieved by making use of an integrating preamplifier circuit having a capacitive feedback element consisting in part of a reed relay which resets the integrator voltage. Since leakage currents can be controlled in all components of the input circuit, the calibrated current range of the system can be extended down to the order of 10−14 A. Resolution of the system as defined by the inherent noise in the integrator circuit is discussed in an appendix note.

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