A contact modulated amplifier to replace sensitive suspension galvanometers.

The electronic amplifier, described herein, is designed to measure extremely small d.c. and low frequency a.c. voltages in low impedance sources. Expressing the electrical noise in terms of equivalent input voltage with a 5‐ohm input resistance and a 5‐milliamp. Esterline‐Angus recorder, the maximum departure from the mean does not exceed 1.5×10−9 volt. Under laboratory conditions the drift is less than 5×10−9 volt over a period of 8 hours. The amplifier is compact and rugged, and it is not affected by vibrations or accelerations experienced in moving vehicles. At present the amplifier is employed in the measurement of radiant energies in infra‐red spectrographs. It is also used for various laboratory and field measurements.