GB793103A - Improvements in or relating to data sensing apparatus - Google Patents

Abstract

793,103. Statistical apparatus. BRITISH TABULATING MACHINE CO., Ltd. Nov. 10, 1954, No. 32534/54. Class 106 (1). [Also in Group XL (b)] Sensing apparatus for a data-bearing document, the significance of which data is determined by the position of the data marks in relation to a start mark, there being a plurality of equally spaced index positions in which data marks may be located, comprises means for feeding the document through the sensing station at a substantially uniform speed so that the start mark and the various index positions are sensed successively, a pulse source controlled by the feeding means for providing pulses at a frequency such that at least four pulses occur between the sensing of successive index positions, a timing pulse generator, under control of the pulse source for producing a pulse coincidentally with the sensing of each index position and means for rendering the timing pulse generator operative under control of the sensing of the start mark. As described, to permit error detection in reading, a two-in-six code is used for recording the data (digits) on the document, any of the digits 0, 1 ... 9 being represented by a start mark S, together with a selective combination of marks in two of the six index positions A ... F, Fig. 1, which show the start and code marks for the digits 0, 9 only. Recording may, alternatively, be effected by holes or magnetic areas. Referring to Fig. 2, the output of a timing pulse generator 8 having a frequency ten times that of the basic frequency (the scanning frequency of the index positions A ... F) is fed to a trigger gate 9 which is triggered by a " leading edge of document pulse " from a sensing head or contact 10 just before the leading edge of each start mark is sensed by its corresponding photo-electric sensing head 12. The timing pulses are then fed to a trigger gate 11 controlled by the digit code mark pulses from the sensing head 12. The output from trigger gate 11 is passed to a frequency halving circuit 13 which, as described in Specification 793,101, functions in combination with a phase reversal circuit 15, also fed from the head 12 and a trigger gate 14, to synchronize the timing pulses delivered by a frequency divider 16 with that " reference " timing pulse which occurs substantially as the centre of the start mark is sensed. Division by ten is effected at 16 so that the output timing pulses fed thereby to a coincidence gate 17 and to a selector 18 occur as the index positions A .. F are sensed. The selector 18 comprises a multi-cathode tube in which the input timing pulses step a discharge successively from one cathode to the next. At the start of a cycle the discharge rests on the first cathode 25 and owing to the double spacing between the start mark S and the first index position A, Fig. 1, the discharge is stepped to the third cathode 19 as index position A is sensed, and to the subsequent cathodes as the corresponding index positions B ... F are sensed in succession. As the discharge rests on each cathode 19 ... &c. a positive pulse is fed to a corresponding coincidence gate 20A ... 20F. Thus should a mark be sensed in any position A ... F of the document, the corresponding pulses from the sensing head 12 are passed via the gate 17 and the associated gates 20A ... 20F to set corresponding triggers 21B ... 21F. Since a two-in-six code is used, two only of these triggers should be operated and this is checked by a " count-two " circuit 22 which responds to the digit pulses passed by the gate 17 and gives a positive output pulse only when two input pulses have been received. This output is fed to a coincidence gate 23 which receives its second input from the selector cathode 27 as the last document position F is being sensed. Provided the check is correct, the gate 23 then passes a pulse .to the triggers 21A . . . 21F whereby those two of these triggers which have been set in accordance with the code marks on the sensed document deliver read-out pulses on their associated output lines 24A ... 24F, after which the various circuit elements are reset, e.g. by a " trailing edge of document pulse," ready for the next cycle. Specification 793,102 also is referred to.