In this paper a digital electronic correlator is reported for use in vibration and acoustic measurements. Two voltage signals, which are reproduced outputs of a multichannel tape recorder, are fed into the analog-to-digital converters of the correlator, and are converted to 4-bits binary numbers at epually spaced sampling instants. One of these digital signals is transported in a shift register delay line and is read out at a later stage to be multiplied with another signal. The products of the signals which are numbers of pulses are accumulated by a counter. To minimize the error caused by drift of the A-D converters, a special method of multiplication and accumulation is adopted, that the product of the compliments of two binary numbers is accumulated as well as the product of the numbers themselves. The shift register has 11 stages and the sampling instant of one of the A-D converters may be shifted with respect to that of the other by a fraction of the sampling interval which is devided into 5 equal sub-intervals, thus giving each 55 discrete steps in positive and negative time shift. The correlation of the input signals is calculated one by one in these steps using samples of the prefixed number which may be set arbitrarilly in the correlator. This device consists of about 400 transistor logical elements and is applicable to the input signals up to 5 KC. Many autc- and cross-correlation functions have been determined with this device. Several of these results are also shown in this paper.
ディジタル型相関器の試作
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