GB893813A - Improvements in or relating to apparatus for representing and storing an analogue quantity - Google Patents

Abstract

893,813. Radar. ELECTRIC & MUSICAL INDUSTRIES Ltd. July 1, 1958 [May 31, 1957], No. 17275/57. Class 40(7). A device for storing an analogue quantity suitable for use in radar equipment automatically tracking the range of an object defines the quantity to be stored in terms of the spacing between disturbances repeatedly travelling between an input point and an output point along a mechanical delay line. In an embodiment the delay line is a nickel wire stretched between suitable supports and carrying a magneto-strictive input coil 2 near one end and a reading coil 3 near the other. A pair of pulses representing the quantity to be stored by their spacing may be fed in at 5 and applied to the line through amplifiers 4a and 4. After passage along the line the pulses are read off, amplified, and applied through capacitor 8 to trigger a flip-flop circuit 9. This provides corresponding reshaped pulses which are fed through gate 6 to amplifier 4a for re-circulation down the line. If the gate 6 is closed by applying an erase potential at 24 the pulses cease to circulate and the store is left blank. To recover the stored information a binary counter 10 feeding gate circuits 11 and 12 is used. The first applied pulse is arranged to trigger the counter to state 0 whenever it occurs thus opening the gate 11 to allow a positive potential from source 13 to charge capacitor 18 through resistor 14. The arrival of the second applied pulse changes the counter to state 1 and opens gate 12 to connect capacitor 18 to negative potential line 16 through resistor 17 so that it discharges. If the time constant of the resistor-capacitor circuit 18, 19 is long compared with the circulation time the potential of the output of the amplifier 15 will reach an equilibrium value corresponding to the ratio of the time intervals: first to second pulse and second pulse to recirculated first pulse. The output will be zero when these time intervals are equal and this condition may conveniently represent zero value of the quantity being stored so that both positive and negative values can be handled by the device. The store is substantially independent of temperature changes. The pulses derived from the line 3 have a sloping front edge and this fact may be used to vary the time of triggering the circuit 9 in accordance with bias applied at 20. Preferably a slope limiter is used to fix the front edge slope and a gate 22 is used to apply bias only during the times when the second pulses pass to the circuit 9. This enables a stored quantity to be modified, for example, by a rate of change input. In a modification short "clock" pulses of 1 mc/sec. frequency are fed to the line continuously and the duration of the information pulses is such that one clock pulse occurs in their length. The flip-flop is triggered only by a peak consisting of the sum of an information and a clock pulse so that the stored information is represented on a quantized scale having an accuracy corresponding to the "clock" pulse spacing along the wire. In this modification a rate of change signal cannot be applied as a bias but may be fed to a Miller integrator which, when the quantity integrated corresponds to the separation between clock pulses, is reset and an additional delay line switched into, or out of, the loop as necessary to cause the second pulses to co-incide with a "clock" pulse adjacent the one with which it would otherwise overlap. It is stated that accurate information as to the quantity stored can be obtained by adding the value stored in the loop to that obtained from the Miller integrator.