Description:
A semiautomatic system has been developed for use with a Lindemann-Ryerson electrometer. The system measures ionization current in the National Bureau of Standards 4π γ-ionization chamber by the Townsend balance-of-charge method. Two minature semiconductor photocells, with associated electronic circuitry, are used for detecting deflections of the electrometer and for controlling the amount of compensating charge placed on the electrometer. In addition, the starting and stopping of an electronic clock is controlled by a third photocell. The system has an ultimate precision of about 0.02%.