GB601985A - Improvements in or relating to electric counting apparatus - Google Patents

Abstract

601,985. Frequency measurements. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. May 14, 1945, No. 12117. [Class 37] The repitition frequency of awaveform is determined by counting the difference in the number of cycles of a known frequency and the waveform traversing respective paths in a predetermined time interval: Preferably, both paths include frequency dividers and the phase of the outputs of each pair of frequency dividers is compared to indicate the difference in the number of cycles of the two waves. The unknown frequency is applied at S, Fig. 2, and mixed at C with a known frequency from G ; the sum or difference frequency is selected at F and applied over a switch circuit G11 to a train of frequency dividers D11, D12, D14; the known frequency from G is applied over a switch circuit G2 to frequency dividers D21, D22, D24, similar to D11 ... 14, and over a further switch circuit G12 to dividers D11 ... 14 ; switches G11 and G12 are operated from a multivibrator M1 so that when one is open the other is shut ; the two trains of dividers are connected by cathode-ray oscillographs PI, P2, P4 indicating the phase difference between the various stages of the trains of dividers. A start pulse applied at SP1 closes switches G2 and G11, and the oscillographs begin to operate to register the phase differences at various stages of frequency division ; at a predetermined time, e.g. onetenth of a second, a stop pulse is applied at SP2 to open G11 and close G12, thus stabilizing the oscillographs at their instant position. The deflections of the oscillographs indicate the unknown frequency. If the dividers D11 ... D14 and D21.... 24 are designed to divide by ten, the oscillographs P1 ... P4 will indicate frequency in units, tens, hundreds and thousands cycles/sec. respectively. The oscillographs are calibrated by using a standard known frequency in place of the unknown frequency.