Patent GB-871476-A (GB)
Title: Improvements in or relating to record sensing machines
IPC: G06K17/00
Filed: 1958-02-26
Abstract: 871,476. Statistical apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Feb. 26, 1958 [Feb. 27, 1957], No. 6221/58. Class 106 (1). A machine for sensing marks representing answers to examination questions has means for scanning the mark positions to generate signals corresponding in amplitude to the quality of the marks sensed, a first circuit responsive to this amplitude for choosing the most well-defined mark in each question and a second circuit responsive to the time of occurrence of the signals for determining the position of the corresponding marks. Different qualities of marks may occur as the result of erasures made by an examinee who changes his answer to a question. The machine finds the most definite mark made in answer to each question and ignores less well-defined marks. For this purpose the first mark found establishes a gating level, later marks being ineffective to influence the interpreting circuit unless they exceed this level. A minimum gating level is imposed in any case so that mark signals of less than a predetermined amplitude are always ignored. A master card bearing the correct answers is sensed to derive signals for comparison with the answer card signals and an accumulator is connected to the comparator to receive the number of correct and/or the number of incorrect answers. The score obtained on an answer card is punched into the card in a predetermined position. Answer card, Fig 1.-The answer card has the shape of an ordinary record card and comprises two sections. Section 1 has space for 40 four-part multiple choice answers and Section 2 has space for 40 five-part multiple choice answers. There are 24 positions across the card, the answer marks falling into sixteen of these in Section 1 and twenty in Section 2. This difference requires a different programme of operations for the two sections which is provided by a programme card and a control panel. The control panel is wired in arrangements corresponding to the layouts of the different sections and the programme card selects the appropriate arrangement of wiring. Sensing answer card.-The marks on the answer card are, sensed photo-electrically, a photo-multiplier tube 11, Fig. 6, co-operating for this purpose with twenty-four neon tubes which illuminate the answer card positions in turn. The neon tubes are alternately accommodated in staggered openings in body 10, the light from each passing through a corresponding hole 13 in plate 12, Fig. 14. The holes 13 for sensing the upper and lower halves of the card are displaced by the spacing of one record card column. This allows the data from upper and lower halves of the card (above and below line A-A) each constituting 12 positions, to be punched in adjacent 12 point columns, on the same card. The upper and lower portions are scanned alternately, the lower portion first, the card being fed by one column before the upper portion is sensed. This is controlled by the programme card. A reference neon is provided which is ignited when no other neon is ignited and thereby gives a standard signal equal to that generated by the light from one of the other neons reflected from a blank position on the card. An output signal is generated only when the reflected light decreases due to the presence of a mark. The neon tubes are connected to a control panel which is connected to allow them to be energized in a sequence appropriate for any possible layout of answer card. The sequence used is selected by the programme card. A ring of triggers set sequentially under the control of a multivibrator is connected through the control panel to light the neon tubes in the selected sequence. Detecting mark quality.-The quality of the marks on the answer card is determined by the circuit of Fig. 21. The output of the photomultiplier is connected through amplifiers 171, 172, cathode follower 173, amplifier 174 and diode 176 to the grid of a cathode follower 177 and to a condenser 178 which is charged by signals through the diode and retains a charge corresponding to the amplitude of these signals. The condenser is discharged by a signal through another diode 179. The cathode of tube 177 is connected to the grid of amplifier 181 connected in turn to amplifier 182 to give an output on line 183. The cathode of tube 177 is also connected to the cathode of amplifier 184 normally biased below cut-off. The output of amplifier 184 is taken via cathode follower 185 to amplifier 186 which produces a signal if the potential of the cathode of tube 177 drops below a predetermined value, set by potentiometer 188 in the grid circuit of amplifier 184. If a poor quality mark is sensed the cathode of tube 177 does not drop enough to cause amplifier 184 to conduct so no output is produced on line 187. The signal on line 187, which is only present at all, if a mark of a certain quality is detected, is used to indicate the quality of the marks for controlling a punch to make a "quality" hole in the answer card during read-out. This precedes the holes indicating the score values accumulated in the counters. Master card.-The master card, Fig. 2, bearing the correct answers is used to compare the answers given by the examinee. This card is mounted on a drum driven in unison with the programme card drum and is sensed by twelve star wheels. The contacts of the star wheels are connected on one side to the stages of the trigger ring and on the other to a common terminal. This terminal therefore produces a signal each time a neon tube is ignited which corresponds to a hole punched in the master card, and this signal is compared with the photomultiplier signal to determine the correctness of an answer. For this purpose the two signals are gated together to produce output signals, one set indicating correct answers and another indicating wrong answers. A control switch is provided which in one position causes both sets of signals to be passed from the comparing circuit and in others causes only the right or wrong answer set to be passed. These signals, according to the setting of the switch, are entered into thyratron units, one for each mark position, the thyratrons being thereby conditioned to fire at the end of each question to set up controlling magnets of a printing or punching machine. Selection of best mark.-To distinguish between poor erasures and good marks, the machine selects the best mark in each question. The condenser 178, Fig. 21, is charged by the sensing of a mark as described above. Condensers in the circuit of amplifiers 181, 182 ensure that a later mark does not cause a signal to appear on line 183 unless an increased charge has been applied to condenser 178 as the result of the sensing of a mark of higher quality. When a mark is sensed a corresponding thyratron is conditioned by the charging of a condenser in the grid thereof, but if a better mark is sensed all these condensers are discharged and the condenser corresponding to the better mark is charged. At the end of the question a pulse causes this thyratron to fire and a corresponding hole is punched in the answer card. Accumulating scores.-Signals representing wrong or right answers are used to set and reset a trigger controlling the gating of pulses to a gas tube counter. There are two counters each composed of dekatrons and control switches determine what is to be entered into each counter. The first counter may accumulate right answers, wrong answers or right answers minus either a half, a third or a quarter of the wrong answers. The fractions are entered from a ring of four triggers which are driven by signals representing wrong answers, triggers being cut out by the control switch as required. The counters are complemented for the entry of subtractive values. The second counter may accumulate right answers, wrong answers or omitted answers. Read out, which takes place under control of the programme card is effected by passing a train of ten pulses into each deketron and using the output to fire a corresponding thyratron. The thyratron sets up punch magnets to punch the score into the answer card. In the arrangement described the contents of the second counter are read out after section I of the answer card to be punched in columns 37-40 thereof. At the end of section 2 the contents of the first counter are read out and punched in columns 75-77. In the next three columns are punched the score accumulated converted according to a predetermined table. Score converting.-If the value in the first counter is positive score conversion may take place after the punching of the actual value in columns 75-77 of the answer card. The conversion is made by using "look-up tables" punched into conversion cards. These are mounted on four drums 437, 438, 439 and 440, Fig. 16, and each sensed by twelve star wheels. The drums escape one column at a time and return to home position after the conversion operation. At each escape four read-out pulses from a trigger ring are entered into the counter, the counter having been complemented immediately prior to read-out. When the counter gives a carry the number of pulses entered will equal the value stored therein. According to which trigger of the ring is set one of the relays 465-468 is energized, to put one of the conversion drums into circuit, say drum 440. The star wheel contacts connect to one of the twelve lines 470-481 which lines are connected in three groups of four to relay coils 485-488 through contacts of relays 482, 483, 484 one of which is energized. The converted score is stored on the table cards on the drums 437-440 in a four-bit binary coded decimal form and relays 485-488 decode this to decimal form for punching and/or printing on the answer card. Contacts of relays 485-488 are arranged in a decoding matrix connected to the interposer magnets for punching into columns 78-80 of the card. Specification 761,520 is referred to.