The reduction in the brownian motion of electrometers

Abstract

A method is described to reduce the Brownian deflections of electrometer systems. This is achieved by replacing the air damping by a special type of artificial damping. The latter is realised by means of a photoelectric amplifier containing a differentiating circuit, comp. fig. 1. The amount of light entering the photocell is made proportional to the deflection of the electrometer system and the output of the amplifier is fed back to the electrometer.

The motion of the electrometer is studied with a photoelectric relay and a recording galvanometer allowing a magnification up to 14300. The application of this method of damping has already resulted in a hundred fold reduction of the Brownian energy and an increase in precision of a factor of ten.

In order to reach the same accuracy with normal air-damping it should be necessary to cool the instrument to 3°K.