Patent GB-1285789-A (GB)
Title: Improvements relating to distance measuring equipment
Inventor: WORTHINGTON WILLIAM DOUGLAS
IPC: G01S13/18
Filed: 1970-03-21
Abstract: 1285789 Pulse radar; transistor multivibrator FERRANTI Ltd 19 April 1971 [21 March 1970] 13778/70 Headings H4D and H3T [Also in Division G4] In a position measuring device a reversible counter 16 (Fig. 1) is cycled at a slow rate relative to a counter 11 the counts in the counters being compared to generate a range pulse RP at equality, this pulse after a delay determined by the count in a range counter 15 being compared with a pulse V the time of arrival of which represents the position being measured to control an indicator 36 and the direction and rate of count of counters 15, 16. As described for measuring position by determining the time of arrival of the return pulse V relative to a transmitted pulse TR sent at the same point of each cycle of counter 11, two consecutive pulses EG and LG are derived from the delayed range pulse RP<SP>1</SP>, counters 15, 16 being stepped at a faster rate until the pulse V overlaps one or other of the two pulses EG and LG. A discriminator 24 then produces sum and difference signals ED and LD which result in the counter being stepped at a slower rate in a direction dependent on which pulse EG or LG the pulse V overlapped more. A velocity counter (FV1-FV6, Fig. 5, not shown) normally in a steady state controls via a D-A converter the current drawn through a transistor (T61, Fig. 6, not shown) of an oscillator to control the frequency of its output pulses. Each output pulse results in a shift pulse VS (Fig. 1) being applied to the counters 15, 16. The faster stepping of the counters is achieved by applying a signal to increase the oscillator frequency. When the pulse V coincides with one of the signals ED or LD the velocity counter is stepped in a direction dependent on the relative times of these signals to adjust the frequency of the oscillator to maintain the pulses EG and LG in register with the signal V. Counting circuits.-The counter 11 comprises fourteen JK flip-flops FP1-FP14 (Fig. 3). The first and second have a source of fast clock pulses applied to their shift input, the second having the output P 1  of the first stage applied to its inhibit inputs. The shift inputs of the third and subsequent stages are connected via gates G35, G36 to the outputs P 1  and P 2  and to a clock source. Each stage P 4 -P 14  has its inhibit inputs connected to the outputs of the previous two stages. Each stage can then only change state when all previous outputs P 1 -P i  are zero. The counter 15 which controls the amount of delay of the pulse RP in dependence on its count by enabling one of sixteen gates to select the point of insertion of the pulse RP into a delay line 22 comprises four JK flip-flops. The range counter 16 is a continuation of the counter 15 and comprises fourteen bi-stables FR1-FR14 the first of which is connected to the output of the counter 15. Each stage receives on its shift input counting pulses VS and on its inhibit inputs the output of gates controlled by the previous stage and direction of count signals DC, IC. Comparator circuit and generation of range pulses.-The comparator 12 comparing the counts in counters 11 and 16 comprises thirteen stages the ith stage for example having a gate receiving the ith outputs RC i  and P i  from counters 11, 16 and a second gate receiving the complements of these outputs. The outputs of the gates are fed to a gate giving an output E i . The outputs E 1  ... E 14  are divided into groups E 1 -E 8  feeding a first gate (G41, Fig. 4, not shown), E 9 , E 10  feeding a second gate (G43) and E 11 -E 14  feeding a third gate (G45), a further gate (G47) being enabled to derive the range pulse RP when all the signals E 1 -E 14  are zero to feed the pulse to sixteen gates (G411-G426) controlled by the counter 15. Range gating.-The outputs of the three gates (G41, G43, G45) are also used with conjunction with a signal on one of three leads (SR, MR, LR) representing the required range to derive a signal RA the mark/space ratio of which represents the range as a function of the full scale range. This signal is fed to the indicator. Modifications.-The two pulses EG and LG may be replaced by a single pulse the counter being controlled in accordance with the relative time of arrival of the pulse V and this single pulse. As described the distance measuring equipment is used in conjunction with a radar system but other types of radiation may be used such as that radiated by a laser source. Transistor multivibrator.-An oscillator (Fig. 6) used in a position measuring device (see Division G4) comprises an emitter coupled vibrator using transistors T61, T62. Resistor 61 is lower than the tail resistors supplying transistor T61 so that the period of oscillation of output pulses W is controlled by the current flowing to transistor T61, this in turn being controlled via a digital to analogue converter by a counter. To initially obtain a high frequency output from the oscillator a signal VP is applied this signal being diverted to a current sink comprising transistor T66 when a signal AGC turns off a transistor T67. A transistor T63 is added to assist the regeneration of very low current values since the transistor T61 draws a much lower current than the transistor T62.