Patent GB-797927-A (GB)
Title: Data reduction system
IPC: H03M1/00
Filed: 1955-11-24
Abstract: 797,927. Analogue/digital interconverters. VICTOR ADDING MACHINE CO. Nov. 24, 1955 [Dec. 1, 1954], No. 33677/55. Class 40 (1). An apparatus for converting an analogue voltage to a digital representation comprises means for sampling the voltage at intervals and converting the value to digital form, there being also provided data storage means to receive the digital values and means for reading out the digital values at appropriate time intervals. A translator is provided in the readout system to convert the digital representations to another form, e.g. to punched record cards. The appatarus may be used to make a record of data produced in analogue form during a test, for example, on a rocket in flight. Since the whole test may be over in a minute or two it is necessary to record the data for future study. The analogue values are therefore converted to digital form and the pulse trains recorded on a magnetic tape. The digital representations are later translated on to punched record cards or printed information for use as required. As shown in Fig. 2, the voltage is sampled at times t1 and t2 and the value converted to square waves, Fig. 3, each having a duration T1, T2 corresponding to the values V1, V2 of the analogue at the sampling points. The square waves are used to gate the output of an oscillator (Fig. 4) to produce corresponding groups of pulses as shown in Fig. 5, which pulses are recorded on a magnetic tape 50, Fig. 1. One track on the tape is used for recording audible instructions and comments through microphone 52. In Fig. 1, transducers 2 to 21 in block 62 receive the test data and convert it into a variable voltage representation, the digital equivalent of which is to be recorded on tracks 2 to 21 of the tape. The signals from the transducers pass to separate attenuators and converters for each track in block 64, the output of which pass to recording heads 66 for the several tracks. A frame speed control circuit 68 provides the timing for the sampling intervals. It consists of a master oscillator and six frequency dividing stages reducing the oscillator frequency of 12 kc. by dividing successively by 10, 10, 6, 2, 5 and 2 so that the final output is one pulse per second. This output passes to amplifier 70 to produce control signals for the input signal converters 64 and to a frame number control apparatus 72. This apparatus also sends a signal to the converters 62 to initiate a frame, i.e. the interval between samplings. A further signal passes to recording heads 74 for channels 22 to 25. Four heads are used to reduce the possibility that the record may be lost owing to a defective area on the magnetic tape. The frame numbering is effected by recording a pulse train having ten pulses for the first frame, twenty for the second, and so on. A monitor 76 which can be connected to any one of the converter outputs displays the number of pulses being recorded. The read-out apparatus comprises reading heads 78, 80, 82 for each track of the tape. The output from channel 1 passes from head 78 to an amplifier and speaker 84. The outputs from the read heads for tracks 2 to 21 pass to a record coder 86 which consists of an electronic counter and which is connected in turn to the read-out heads, the full length of tape being passed under each head while the coder is connected to it. A manually preset frame speed control 88 governs the time constants of the coder to allow it to receive signals having frame lengths of, for example, one second, one-tenth or one-hundredth of a second. The signals from the timing tracks 22 to 25 are picked up by heads 82 and applied to a frame coder 90 which provides a pulse at the beginning of each frame and a pulse group proportional in number to the frame serial number. The output of the record coder 86 is passed to a relay matrix 92 in which the data is stored to be read-out later to apparatus 94 which may be a card punching machine, or a printing or listing machine. The frame coder 90 supplies a signal to a relay matrix 96 which in turn supplies the value registered to the read-out apparatus 94 so that the number of the frame will be punched or printed simultaneously with the digital value. After the read-out apparatus 94 has completed its operation it gives a signal which is applied to the coders 86 and 90 to trip all the relays. The read-out apparatus makes a punched card, for example, for each sample point of the voltage produced by each transducer the card bearing a numerical representation of the value of the voltage at the time to which the card corresponds. Other information may be recorded on the card as required. Analogue to digital converter.-The varying voltage, Fig. 2, is applied to terminal 116, Fig. 7, a switch 114 being provided to connect this terminal or another 118 through an attenuator 111 to an amplifier 110. A standard voltage is applied to terminal 118 whereby the apparatus is calibrated. The output from the amplifier on line 122 varies between zero and fifty volts. This is connected through diode 126 to the grid of cathode follower 128 and the plate of pentode 130. Line 134 is held at about 105 volts by connection through resistance R140 to positive line 132. The grid of pentode 130 has a variable voltage applied to it from a potentiometer between lines 132 and 134. This voltage is also applied to a condenser V150 connected to the cathode of the triode 128. Pentode 130 forms part of a phantastron circuit, the run-down cycle of which is initiated by a positive pulse across resistor R156. During the run-down portion of the cycle current passes through the plate of pentode 130 to produce a voltage across resistor R151 which by means of cathode follower 128 serves to charge condenser C150, the charging time governing the duration of the run-down cycle. The rate of charge depends upon the value of resistor R148 and the potential applied to the cathode follower from the amplifier 110. There is little current in resistor R152, and consequently only a small voltage across it, during the run-down period. During the rest period of the cycle the whole cathode current comes through the control grid so that a large voltage is produced across resistor R152. The pulse which starts a run-down cycle at the beginning of a frame is derived from a square wave pulse emitted by the frequency dividing arrangement and transmitted on line 160 at intervals of one second. Coupling condenser C162 and diode 164 produce a sharp-fronted positive pulse as shown in Fig. 3. The screen grid of pentode 130 is connected to a -150 v. line through resistors R168, R169, the centre point of which is connected to the grid of gating triode 172, the cathode of which is connected to the master oscillator via line 174. The plate of this tube is connected to the primary of a transformer 179. Triode 172 acts as a gate, opening during the run-down period of pentode 130 to pass the 12 kc. signal from the oscillator through the transformer to output terminals 192, 193. The pulse train produced has a number corresponding to the transducer voltage at the sampling point and is recorded on a track of the magnetic tape, the recording frame being governed by the output pulses from the frequency divider referred to below. Read-out.-The pick-up head selected for reading out has a sine waveform voltage induced in it which is amplified and used to operate a trigger circuit. The pulses from this trigger pass to a counter consisting of four decimal counter units consisting of four tubes. The first counter merely serves as a means of dividing by ten and can be cut out if the frame lengths are only one-tenth of a second. For one second frame lengths it remains in circuit and passes every tenth pulse to the second counter. Twelve leads, three from each of the last three counters are brought out, the total count being indicated by a particular pattern of voltages on these lines. The signals on these lines are amplified by triodes and used to energize self-holding relays. The count represented by the set-up of relays is taken by the read-out device and recorded by printing or punching record cards. The relays are then tripped to allow the next count to enter.