D-C Amplifier Stabilized for Zero and Gain

An electronic amplifier for d-c measurements is described in which the zero is stabilized by the use of a contact type of modulator vibrating at 60 cycles per second. The gain is stabilized, by over-all d-c feedback, to a small fraction of one per cent. Circuits and precautions are described which have been used to adapt this type of amplifier to the measurement of contact potential drop, thermocouple electromotive force for infrared gas analysis, electromotive force of glass electrodes for pH determination, and current from capacitors resulting from leakage and absorbed charge. The relation between noise from thermal agitation and the system response is discussed.