An Inexpensive Vacuum-Tube Electrometer

Abstract

This paper describes a simple, yet accurate, vacuum-tube electrometer that has proved very useful in the teaching laboratory for measuring the small currents involved in various modern physics experiments. Details of the circuit design and construction are given. In addition, an electrometer test setup is described and the results obtained with the electrometer here considered are presented. The results indicate that this unit has an over-all precision of better than 4% on its 10−10 A full-scale range and a response time (including the recorder) of less than 12 sec for full-scale travel following application of a step function input. A simple modification allowing measurement of resistances up to 1011 Ω is also indicated.

Bipolar transistors can detect charge in electrostatic experiments

“…Since the beginning of investigations of electricity, versoria and, later, electroscopes were used [1,2]. Vacuum tubes offered much greater sensitivity, see [3,4]. Field effect transistors (FETs) enabled both extremely simple [5] and very sensitive [6][7][8] detectors.…”