Versatile Amplifier for Precise Radiometry

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Abstract
An amplifier is described that is suitable for the precise measurement of chopped radiation at very low intensity. It can be operated with all types of detectors used in such measurements, including thermopiles, bolometers, Golay cells, photomultipliers, photoconductive cells, and photoemissive cells, and in all cases the minimum detectable signal is determined only by the inherent noise of the detector. Comprehensive descriptions of the circuits, their principle of operation, and performance figures are given. Chopping frequencies between 5 cps and 1 kc can be used, and the amplifier gain is stabilized and defined by the application of feedback. It is shown that an electrical signal of 10−6 V rms from a 22‐Ω source can be measured to a precision of 0.1%, while with very small signals such as 10−9 V rms, the precision is limited only by the amount of noise present at the detector.

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