Patent GB-591928-A (GB)
Title: Improvements in or relating to electric phase measuring apparatus
IPC: G01R25/00
Filed: 1945-05-12
Abstract: 591,928. Phase-difference measurements ; cathode-ray oscillographs. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. May 12, 1945, No. 11986. [Class 37] An arrangement for calibrating directly in phase angles the screen of a cathode-ray oscillograph employed for giving indications of phase difference between two waves comprises means including the phase difference determining circuits for producing an auxiliary wave to deflect the electron beam in a cyclical path and means for varying a characteristic of the beam at predetermined intervals of time during the cyclic period of the auxiliary wave. The waves W1, W2, the phase difference of which is to be measured, are applied to amplifiers A1, A2, the output from A1 being much greater than that from A2. These outputs are applied to filters F1, F2 to produce substantially sine waveforms in the outputs thereof. The outputs from the filters F1, F2 are applied to a phasesplitting bridge network PS comprising alternate resistance and capacitance arms R1, C1, R2, C2. The output from the filter F2 is phase split so that the voltages across the diagonals P, Q and P1, Q1 are in quadrature, whilst the output from the filter F1 is applied to all the points P, Q, P1, Q1 in the same phase. The potentials at the points P, Q, P1, Q1 are applied through rectifiers r2, r4, r1, r3 to the deflecting plates X1, X2, Y1, Y2 of the cathode-ray oscillograph. Steady deflecting voltages are obtained by means of resistance-capacitance time circuits n1, n2, n3, n4, which integrate the effect of the waves. The spot on the oscillograph screen takes up a position depending on the phase difference between the waves W1, W2. For calibrating the oscillograph an oscillation generator G, which may be crystal controlled, has its output frequency F frequency divided to produce two different frequencies differing by a low frequency f. The output from G is divided in a frequency divider D11 by a factor of 7 and in a frequency divider D21 by a factor of 6. The output from D11 is then divided in a frequency divider D12 by a factor of 5 and the output from D21 is divided in a frequency divider D22 by a factor of 6. The frequency in the output of D12 is then F/36, the difference in frequency f between these outputs being F/36 Î 35. If the output of D12 is connected to the input of the filter Fl and the output of D22 to the input of the filter F2, there will be produced at the points P, P1, Q, Q1 quadrature phases of a frequency 35f and like phases of a frequency 36f, causing rotation of the electron beam around the oscillograph screen at the difference frequency f. The output from the divider D11, which has a frequency of 180f, is applied to a differentiating circuit D1 and the short pulses obtained are applied to the intensity control grid IG of the oscillograph so that the intensity of the beam is varied every two degrees of rotation of the beam and a series of bright spots on a circular scale is produced. In order to obtain tendegree divisions, the output from D12, at a frequency of 36f, is applied to a differentiating circuit D2, the output from which may be applied in series with the output from D1, or alternately therewith, to the control grid IG. Every fifth spot, or 10 degrees, then appears brighter than the intermediate spots representing two-degree divisions. The calibrating waves and the waves W1, W2 are applied alternately to the filters F1, F2 by manually or automatically operated switching means, the calibration scale persisting and enabling the phase difference to be read directly. For bearing determination, a comparison wave may be derived from the output of D12 or F1 and takes the place of the wave W1. A switch S3 enables condensers to be inserted between an earth potential point and all the oscillograph deflecting plates, reducing the effect of noise currents contained in the waves W1, W2.