Precision Integrator for Beam Current

Abstract

A current integrator has been built in which a servo is used to charge a capacitor in discrete amounts so as to match within certain limits the integral of an input current. By keeping the discrete charge small and the repetition rate for the incremental charge high, one can for practical purposes achieve continuous operation. An instrument accurate to better than 0.1% and with input impedance of 5×104 ohms for the current range 0.1 to 30 μa is described.