An automatic frequency comparator
N F Astbury · Journal of Scientific Instruments · 1935
An arrangement is described by means of which the beats occurring between two frequencies are automatically counted and timed. The apparatus is at present used to compare frequencies of 100 cycles per second and 1000 cycles per second, beats being obtained between the latter and the 10th harmonic of the former, but it is generally adaptable. The counting and timing circuit, a feature of which is the accurate and "fool-proof" starting and stopping arrangement, can be used separately to time any recurring event.