GB1085836A - Improvements in or relating to digital data averaging apparatus - Google Patents

Abstract

1,085,836. Electric selective signalling. ELECTRIC & MUSICAL INDUSTRIES Ltd. June 8, 1964 [June 8, 1963], No. 22934/63. Heading G4H. A pulse train is averaged by obtaining the difference of the numbers of signals from two sources responsive to the pulse train delayed and undelayed respectively. Referring to Fig. 1, the speed of steel strip 1 in a rolling mill is measured by measuring the time surface graining on the strip takes to travel between photo-cells 2 and 3. The photocell outputs are passed through wide band A.C. amplifiers 4, 5, and then converted to pulse form (rectangular waves) by limiters 6, 7. The output of limiter 6 (fed by the first photocell reached) is delayed by being shifted along a magnetic-coretype shift register 8. The contents of two stages of register 8 are subtracted at 10 and the difference compared in correlator 11 (half-adder or diode modulator) with the current pulse of the train from limiter 7. The resulting pulse train from correlator 11 is smoothed (or averaged) by a shift register 12 and gates 13, 14. The outputs of gates 13, 14 respectively increase and decrease by one the count of an accumulator (counter) 15, gate 13 producing an output when the input and output of store 12 are + and - respectively, and gate 14 producing an output when the reverse holds. The count is converted to analogue form at 16 to control the frequency of oscillator 9, the pulses from which constitute the stepping pulses for shift registers 8, 12 and the system output. The analogue output from 16 constitutes a fine error signal and is combined with a coarse error from rate comparator 17 (no details) and integrated acceleration feed-forward from 18, to control oscillator 9. Alternatively, the error signal could be used to control the strip speed instead of the oscillator, the frequency of which would thus determine the speed reached. A ternary modification uses two registers 12 and gates corresponding to 13, 14 supply +2, + 1, 0, - 1, - 2 signals to the accumulator 15. Fig. 2 (not shown), shows a modification of Fig. 1 in which: (a) subtraction and correlation occur in the reverse order; (b) the output of the subtracter is also used to produce an error rate signal (representing the average rate at which pulses are delivered by the subtractor) which is combined with the other error signals for improved stability at high loop gain; (c) a magnetic drum or tape is used in place of the shift registers and clock pulses recorded thereon in place of the oscillator, the speed of the drum or tape being controlled (in the " measuring " alternative) by the signals previously used to control the oscillator frequency; (d) transfer from coarse to fine control may be produced under control of the two correlator outputs (summed); and (e) sampling of the amplifier and limiter outputs is provided. Two of the above measuring systems may be provided to obtain the ratio of ingoing and outgoing strip speeds in a rolling mill (or one minus this ratio), arrangements utilizing counters being described for this purpose.