Patent GB-609298-A (GB)
Title: Improvements in or relating to electrical apparatus responsive to the phase difference or time lag between two periodic energy waves
IPC: G01R25/00
Filed: 1942-01-03
Abstract: 609,298. Measuring phase - differences. SPERRY GYROSCOPE CO., Inc. Jan. 3, 1942, No. 116. Convention date, Jan. 22, 1941. [Class 37] The phase-difference between alternating quantities is measured by means of an indicator connected into circuit over periods corresponding to the phase-difference. Thus in Figs. 2, 4, the points a, b, &c. correspond to moments when the two quantities cross the axis in the positive direction and a switch 1 is arranged to close at point a and open at point b. If Im, is the current which would flow if meter 4 was continuously energized (corresponding to a phase-difference of 2#) and I4 is the actual meter current, then I4/Im=#/2# or I4 is proportional to #, the phase-difference to be measured. If a two-way switch 5 were employed, Fig. 5, to make at 6 the circuit of meter 4<1> at point a and at 7 to make the circuit of meter 8 at point b, then meter 4<1> would read # and meter 8 would read (2# - #), this latter reading decreasing as # increased. A similar arrangement could be obtained by connecting a single meter 9, Fig. 6, so as reversely to be energized by # and (2# - #) according as 6 or 7 was engaged. By employing a centre-zero meter, readings less than 180 degrees would cause movement to one side and greater than 180 degrees to the other, whereas if the centre of the scale is zero phase angle, positive and negative angles are respectively to one side or the other. Where the frequencies are too high to allow of mechanical switching, thermionic triggering valves 14, 15 are employed in conjunction with a differential meter 26 having a winding connected to each valve. Resistances 19, 20 are connected between the plate of valve 14 and the earth lead 21, the common point 28 being connected to the grid of valve 15 which is provided with similar resistances 19<1>, 20<1> and connection from point 28<1> to grid of 14. The reference voltage V4 is applied to an amplifier 23, the output of which is taken over a voltagelimiting diode 24 to a pulse circuit comprising a condenser 30 and resistance 29, and to a valve 25, the anode of which is connected to point 28. Voltage VB under test is fed to a circuit denoted by similar, but primed, references. When the voltage of the plate of valve 23 reaches the point corresponding to a in Fig. 2, a high rate of change of voltage is transmitted by condenser 30 to valve 25, the plate-current in which lowers the potential of point 28 and hence of grid of valve 15 (which was previously carrying current), so that the plate-current of 15 is reduced and the platepotential thereof is raised and hence that of 28<1> is raised. Grid-potential of 14 is raised to pass plate-current in 14, so lowering the voltage of plate of 14 and hence of point 28 still further. The action proceeds until 15 is cut off entirely and 14 is conducting and remains so until point b is reached in amplifier-plate 23<1> when a similar cycle of operations transfers the current-flow back from 14 to 15. Meter 26 has its windings on a common armature or operating on a common shaft as in Fig. 6, but may be replaced by an arrangement as in Fig. 5, or by one in which the meter 4<1> or 8 is replaced by a resistance. In Fig. 10 (not shown) each amplifier 23, 23<1> is preceded by a voltagelimiter, amplifier, phase-inverter and voltagelimiter to which the voltage is originally applied, and the phase-inverter in one side is capable of being short-circuited so as to change the scale-readings of the meter by 180 degrees. Where the phase-difference at radio frequencies is to be measured, they are heterodyned with locally-generated oscillations differing in frequency from them by audio-frequency, which is then fed to the phase-difference indicator circuit, Figs. 11, 12 (not shown). The voltagelimiters and pulse circuits can be replaced by saturable transformers or chokes, Fig. 13, showing one form in which transformers 41, 41<1> in the anode circuits of valves 23, 23<1> energize valves 25, 25<1>, the anode circuits of which contain transformers 40, 40<1> connected on the secondary side to points 28, 28<1> and the control grids of valves 14, 15, or they may be connected between points 28, 28<1> in series with condensers to the earth lead, Fig. 14 (not shown). The saturable chokes are also arranged in the anode circuits. The meter arrangement of Fig. 13 is as in Fig'. 5, with a resistance replacing one meter and the other shown as a recording instrument.