Patent GB-588187-A (GB)
Title: Improvements in pulse echo distance measuring devices
IPC: H03K5/159
Filed: 1944-06-21
Abstract: 588,187. Radiolocation ; thermionic valve circuits ; artificial lines. WESTERN ELECTRIC CO., Inc. June 21, 1944, No. 11840. Convention June 22, 1943. [Classes 40 (iii) and 40 (v)] [Also in Group XXXV] In a pulse-echo distance measuring system, means are provided for automatically maintaining a reference pulse in coincidence with an echo pulse to provide a continuous indication of distance by controlling the time relation of the reference pulse by a control means which is itself jointly controlled by the reference and echo pulses. A pulse radar system is described, but the invention is stated to be applicable to any form of energy pulses and may be used for determining the distance to a reflecting area beneath the surface of the earth or a body of water, or the distance to breaks or obstructions in transmission lines or pipes. In Fig. 1 a pulse from the pulse generator 13 controlled by the oscillator 12 triggers off the transmitter 14 and is also fed through the shaping amplifier 16, low-pass filter 21 and linear amplifier 22 to the variable-delay line 23 to give a delayed pulse A, Fig. 7, which initiates in circuit 24 a first gate pulse D, the trailing edge of which initiates a second gate pulse H. Echo pulses received at 18 are fed through the fixed delay 43 to the amplifiers 28 and 29, the outputs from which are applied together with the gate pulses to the integrator circuits 26 and 27. The integrator valves are so biassed, E and F, Fig. 6, that only the tops of the gate pulses together with any superimposed echo signals appear in the outputs G and H, Fig. 6, and these outputs are separately amplified at 44 and the difference of the resultant outputs applied to the modulator 45 of the automatic control system. When the echo pulse is equally distributed between the two gate pulses, the difference output from the amplifier 44 is zero, but when the echo is displaced from this condition an error voltage is produced, the amplitude of this voltage being proportional to the amount of displacement and the polarity depending on the direction of displacement. This error voltage is used to control a two-phase A.C. motor 48 which varies the delay in the line 23 so as to automatically centre the gate pulses about the echo pulse. An additional motor may be provided in the mechanical output unit 49 which follows the motor 48 as shown in U.S.A. Specification 2,056,348, and may be used for operating an optical range-under or computer. The delay is a measure of the range which may be indicated directly by a dial 500 connected to the motor or to the getting of the delay line. The delay line gives the delay to the leading edge of the first gate pulse, but the echo is centred around the trailing edge of this gate and in order to compensate for this and any minimum delay in the line, a, fixed delay 43 is introduced. in the signal circuit. Variable delay line, Fig. 2. This comprises a number of sections with single sections between adjacent tapping points IN 0 to IN 11 connected to the contacts of the rotary input switch No. 1 and twelve sections between adjacent tapping points OUT 0 to OUT 11 of the rotary output switch No. 2. The two switches are ganged through the counter gear 97 so that in operation the input tapping moves to the left from IN 0 up to IN 11, further movement of the switch returning the input tap to IN 0 and moving the output tap from OUT 0 to OUT 1. By this means 144 delay steps are obtained with only 24 tapping points. To compensate for the changing attenuation caused by varying the tapping point, the output taps are brought out from the capacity dividers 100 to 110, the capacity ratio of the two components being varied along the line. Alterna- Lively, the switch contacts may be in a straight line with an appropriate linear return motion for the switchmg arm. The inductance components of the line are wound on a long former, the mutual inductance so obtained introducing an equivalent negative inductance in series with the shunt condensers which provides a constant delay for all frequency components of the pulse up to the 2 Mc/s. cut-off of a low-pass filter through which the input to the line is applied. Thermionic valve circuits, Figs., 3, 4, 6 and 7. The delayed pulse A, Fig. 7, from the delay line 23 is shaped in the unbiassed distorter-amplifier V3, an inductance 128 being provided as part of the anode load to maintain equal amplification of the high frequency components of the pulse, to give a sharp pulse B. This pulse is further amplified in V4 which is normally cut off by the high positive cathode bias derived from the potentiometer 145, 147 and the negative output pulse shock-excites the tuned circuit T1 in the grid circuit ofV5 to produce the oscillation C which is heavily damped after the first quarter cycle by grid current V5. V5 is unbiassed so that the wave-form C produces in the anode circuit a square gate pulse D which is differentiated by the CR circuit 170, 171 giving a wave form E which produces a second gate pulse H in the second gate-forming circuit 25 comprising valves V7, V8, and V9. Circuit 25 operates in a similar manner to the first gate-forming circuit 24 and the electrode potentials E to J are derived from corresponding points on circuit 24 in order to conserve components. Due to the high positive cathode bias on V8, only the second positive pulse 428 of the input F is effective so that the leading edge of the second gate pulse H is coincident with the trailing edge of the first gate pulse D. The amplitude of the two gate pulses is limited by the shunt diodes V6, V10 the cathode bias of which is derived from the cathode bias of V13 via the point M and the gate pulses are applied together with the positive echo signals from the unbiassed video amplifiers V11 and V12 to the integrator circuits 26 and 27. These comprise valves V13 and V14 which are cut off by the large positive cathode bias derived from the potentiometer 275, 277 and 278 so that only the tops of the input gate pulses together with any superimposed echo pulses, E and F, Fig. 6, produce anode current flow G and H. The video signals are limited below the cut-off levels of V13 and V14, so that signals not occurring within the duration of the gate pulses do not affect the .outputs from V13 and V14. These outputs are integrated by the long time constant circuits 286, 287, 288 and 297, 298, 299, amplified in the double triode DC amplifier V15 and applied to the double triode DC cathode follower V16, the difference of the outputs across the cathode loads 324 and 325 being used as the error voltage for the automatic, control system. Automatic control system, Fig. 4. The error voltage is applied together with a 90 degree phase shifted 400 c/s voltage from 47 to the balanced modulator 45 which may be of the type shown in U.S.A. Specification 2,025,158. The amplitude of the 400 c/s output is proportional to the magnitude of the error voltage and the phase changes by 180 degrees with changes in the polarity of the error voltage, Fig. 8 (not shown). This output is amplified at 46 and applied to one winding 400 of the two phase motor 48, the phase of this voltage being 90 degrees advanced or retarded with respect to a 400 c/s voltage applied to the other winding 401 direct from the source 47 according to the polarity of the error voltage. Thus the direction of rotation of the motor 48 and consequent variation of the delay 23 depends upon the direction of inisalignment of the echo pulse with respect to the gate pulse. Manual control of gate pulses, Fig. 4. The gate pulses can be made to scan the time trace by unbalancing the DC amplifier V15 by means of the variable tapping 304, and the pulses will then lock onto any echo pulse that they may encounter during the scan. The gates may be set on any desired echo by the push-button manual control 450 which unbalances the D.C. cathode follower V16 by earthing either of tho grids, the unbalance being so strong that the gates rapidly scan the trace without locking on any intervening pulse. In a modification, Fig. 5 (not shown), the delay artificial line is replaced by a delay circuit such as shown in Specification 582,228 in which the variable delay is controlled by the setting of an R.C. delay circuit and ganged phase shifter. A cathode ray tube display is shown in which the echo signals are applied to one Y-plate and gate markers derived from the gate pulses are applied to the other Y-plate, the position for automatic control being when the echo pulse is centred within the gate markers. Specification 477,875, [Group XXXV], also is referred to. In the Specification as open to inspection under Sect. 91 it is stated that the invention is applicable to maintaining synchronism or any desired time relationship between any two series of pulses which have similar spacing in time but the spacing of one of which is varying from that of the other. This subject-matter does not appear in the Specification as accepted.