A theory of the 'operational' count ratemeter is described. The ratemeter has two or more CR circuits combined with operational amplifiers and can be used with various frequency responses. The relations between time response, frequency response and the statistical fluctuations of the output are presented. A simple circuit using two CR pairs is proposed, and the formulae for its performance are given. The response can be adjusted to yield critical- or under-damping. A critically-damped or a slightly under-damped ratemeter provides a faster response for a sudden change in radiation intensity than conventional ratemeters. For a band-limited input signal, the under-damped ratemeter can enhance the varying component of the signal.
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