Patent GB-684831-A (GB)
Title: Improvements in or relating to electrical phase measuring apparatus
IPC: G01S13/70
Filed: 1947-07-15
Abstract: 684,831. Phase difference measurements. SPERRY GYROSCOPE CO., Inc. July 15, 1947 [July 16, 1946], No. 18832/47. Class 37. [Also in Groups XXXV and XL (c)] The time interval between particular phases of two signals is measured by automatically selecting periodic pulse waves, measuring the time interval between two such selected pulse waves, and providing a continuous indication thereof which is substantially undisturbed by periodic interference or random noise. Fig. 1 shows an apparatus for determining the time interval between pulse waves of the same repetition rate from sources 12, 13 of reference and delayed signals, a continuous reading being provided by an indicator 14. A high-frequency oscillator 15 is employed as a standard and is connected to a frequency divider 16 which reduces the generated frequency to approximately that of the reference and delayed signals. The waves of reduced frequency are supplied to a pulse wave generator 18 producing trigger pulse waves which are applied to a coincidence circuit 21, to which is also applied the reference signal from the source 12. The coincidence circuit 21 produces rectangular frequency control waves 46, Fig. 3, when triggered by the generator 18, the amplitude of these pulses being proportional to the amplitude 43 of the reference signal 41 at the moment the circuit is triggered. The frequency control waves are supplied to a selective averaging circuit 24, described in Specification 684,901, through which there are two paths to the frequency control circuit of the oscillator 15. The first path is normally effective and permits the frequency control circuit of the oscillator 15 to respond to individual frequency control waves when the oscillator 15 is not synchronized with the source of reference signals 12. The second path is normally ineffective and is rendered effective in response to an average amplitude of the frequency control waves about some predetermined level in such manner as to disable the normal conductive path. The means for averaging the frequency control waves is inserted when synchronism has been established in order to maintain this condition with a high degree of discrimination against random noise and other interference. The frequency divider 16 is also connected to a phase shifter 27, the shaft 28 of which is coupled to the indicator 14. The phase-shifted waves are applied to a pulse wave generator 29 which is similar to the generator 18. The trigger waves from the generator 29 are fed to a coincidence circuit 31, corresponding to the circuit 21, to which are also applied the delayed signals from the source 13. Control waves 48, Fig. 3, are produced having amplitudes in accordance with the instantaneous amplitudes of the delayed signals 42 from the source 13 and are fed to a selective averaging circuit 33 similar to the circuit 24. The selectively averaged control waves from the circuit 33 are supplied to a servo amplifier 34 which energizes a motor 35 actuating the shaft 28 of the phase shifter 27. The pulse waves 46, Fig. 3, are provided by the generator 18 in response to a wave 47 from the frequency divider 16 while the pulse waves 48 are created by the generator 29 in response to the phase-shifted wave 49 fed from the phase shifter 27. When the pulse waves 46, 48 coincide with similar portions of the wave fronts of the signals 41, 42 the phase shift of the wave 49 with respect to the wave 47, as indicated by the indicator 14, represents the periodic interval between corresponding phases of the delayed and reference signals. Until this synchronous condition has been established the oscillator 15 operates at a frequency such that the trigger waves 46 from the generator 18 occur at a slightly slower rate than do the reference signals 41. Since the intervals between the pulse waves 46 are longer than those between the reference signals 41, they tend to overtake them and increase in amplitude as the point of coincidence shifts from the desired coincidence point 43 to the peak of the wave 41, so that a frequency control wave is produced which increases the frequency of the oscillator until the trigger pulses 46 are brought to the desired coincidence point 43. In a modification, Fig. 2, the servo-amplifier 34, motor 35, and phase-shifter 27 are replaced by an oscillator 71 and frequency divider 72, the delayed signals being synchronized similarly to the reference signals. A phase - meter 73 measures the phase angle between the waves from the frequency dividers 16, 72. Alternatively an interval meter 74 as described in Specification 606,269 may be employed to measure the interval between the trigger pulse waves from the generators 18, 29. The pulse wave coincidence circuit 21 is shown in Fig. 7. A quiescent blocking oscillator 81 is adapted to be triggered by pulse waves applied over the lead 19 from the pulse wave generator 18. A charge-collecting capacitor 82 couples the anode 83 of the blocking oscillator valve 84 to the grid 85 of a valve 86 in a cathode follower circuit 87. The grid 85 is also connected to the junction of the anode 91 of a diode 88 and the cathode 92 of a diode 89. A positive voltage is applied through a load resistor 93 to the cathode 94 of the diode 88 and the anode 95 of the diode 89 is earthed, so that a bias potential is applied to the diodes 88, 89 tending to oppose current flow. A charge on the capacitor 82 is electrically isolated over a range of voltage from the earth potential on the anode 95 to the positive potential on the cathode 94. A cathode follower circuit 96 impresses on the load resistor 93 a version of the reference signals applied over the lead 22 from the source 12, so that the potential on the cathode 94 is proportional to the sum of a constant bias potential and the momentary amplitude of the reference signal. The blocking oscillator 81 when triggered produces a single exploratory pulse wave 101. With the blocking oscillator 81 blocked, the capacitor 82 charges through the diode 88 to the difference of potential between its cathode 94 and the anode 83 of the valve 84. On the downward swing of the blocking oscillator the decreasing anode potential forces the voltage on the grid 85 to zero, but it is prevented from going negative by discharge from the capacitor 82 through the diode 89. On the return swing of the pulse wave 101 the potential on the grid 85 rises to that of the cathode 94 but is prevented from going higher by current flowing through the diode 88 to recharge the capacitor 82, which continues to charge until the pulse wave 101 reaches its maximum value. The voltage drop across the capacitor is then equal to the difference between the maximum potential of the anode 83 and the instantaneous potential on the cathode 94. When the wave 101 returns to its quiescent value the charge on the capacitor 82 remains unchanged and the potential of the grid 85 is reduced to the difference between the instantaneous potential on the cathode 94 and the upward excursion of the blocking oscillator pulse wave. The amplitude of the upper excursion of the wave 101 is constant, as is the bias on the cathode 94, consequently the potential to which the grid 85 is returned is proportional to the magnitude of the version of the reference signal which is applied to the cathode 94 by the cathode follower 96. The voltage on the grid 85 remains constant over the entire period between the trigger pulse waves, and the cathode follower 87 reproduces this control voltage at low impedance for supplying the frequency control circuit of the local oscillator 15.