The rapid recognition of a significant increase in the rate of arrival of pulses occurring at random
There is a fundamental lower limit to the time in which it is possible to recognise an excursion in the mean rate of pulses occuring at random and to distinguish it reliably from a chance fluctuation. This lower limit is found and is evaluated numerically for the case of an exponential excursion. It is possible to build relatively simple electronic equipment which will give indication of such an excursion in little more than the absolute minimum time over a wide range of conditions of initial pulse rate and of excursion period. An example of such a circuit is described and is shown to be capable of responding in less than one period of the excursion or in less than the time to count 200 pulses at the initial rate, whichever is the greater. This circuit will give false indication only on extremely rare voltage fluctuations exceeding 10 standard deviations, which are of negligible probability per year. It is suggested that the method described may be of use to give rapid warning of excursions in reactors and critical assemblies. In any case, the theoretical optimum found constitutes a standard of reference by which equipment for such warning may be judged.