GB844215A - Improvements in the reading of digital data signals - Google Patents

Abstract

844,215. Photo-electric reading of digital data records. DIRKS, G. May 13, 1957, No. 15068/57 Class 40(3). A plurality of digits represented by spaced apart groups of optically readable marks, each group representing a digit by the number of marks in that group, are read by an apparatus including, sensing means for optically scanning the groups of marks in succession to produce a signal pulse for each mark, detecting means controlled by the signal pulses and adapted to generate a control pulse in the interval between the sensing of successive groups of marks, a pulse counter adapted to be operated by the signal pulses, and signal gating means controlled by the detecting means and adapted to cause additive entry into the counter of one or more of said plurality of digits and subtractive entry of another two or more of said plurality of digits. In the exemplified embodiment a record sheet, Fig. If, is provided with groups C3, C2, Cl and A3, A2, Al of marks representing the numbers "573" and "265" and with groups of marks D2, D1 and B2, B1 representing check numbers "15" and "13" obtained by cross addition of the digits of the numbers "573" and "265" respectively. The groups of marks C3, C2, Cl, D2, D1 are scanned by a photo-cell 25, Fig. 2, and the groups A3, A2, Al, B2, B1, by a photo-cell 26, producing pulses which are stored upon an intermediate storage member 27 and which are also applied to control stages 28, 29. In each of the control stages 28, 29, the check number digits represented by groups of markings D2, Dl and B2, Bl respectively are set upon a pair of counting tubes after which the individual pulses due to the groups of markings C3, C2, Cl and A3, A2, Al are fed to the counting tubes in the direction 9-0. If these pulses reduce both counting tubes in each control stage to zero, which indicates that the numbers represented by the groups of markings have been correctly transmitted, a pulse from each control stage 28, 29 is delivered to an amplifier 98 which then initiates release of the signal recorded on the intermediate storage member to the magnetic storage tape 30. In the control stages, the gating of the various groups of pulses to the counting tubes is controlled by flip-flops responsive to and generating control pulses in the intervals between the groups of pulses. If one or both of the control stages 28, 29 does not produce a pulse indicating a correct transmission of the readings, the record sheet is automatically returned to its starting position for a repeat of the scanning operation.