Patent GB-636103-A (GB)
Title: Improvements in and relating to phase-sensitive modulators
IPC: G01R25/00
Filed: 1945-05-31
Abstract: 636,103. Phase indicators; power meters. BRITISH THOMSON-HOUSTON CO., Ltd. May 31, 1945, No. 13703. Convention date, June 1, 1944. [Class 37] [Also in Groups XXXVIII, XXXIX and XL (c)] A reversible A.C. or D.C. modulator comprises four rectifiers, each having a high threshold value of resistance, connected in a closed series assisting circuit. An A.C. supply is connected across one diagonal and is shunted by an impedance, and a D.C. signal circuit is connected across the other diagonal, while an A.C. signal is connected between one end of the latter diagonal and a tapping on the impedance. The modulator is reversible to produce a current in the D.C. signal circuit dependent in magnitude and polarity on the amplitude and phase sense, relative to the supply, of the A.C. signal, or vice versa. Fig. 2 shows a series assisting network of rectifiers 23, 24, 25, 26 diagonally connected to points on a shunt impedance 22<1> across an A.C. supply 27. A D.C. meter 12 is connected through switch 30 to the other rectifier network diagonal, one terminal of which is connected to the shunt impedance mid-point tap 23<1> through switch 31, the centre-point of a balanced transformer winding 19, 20 and the tap of a potentiometer 21 shunting the winding which is variably coupled to the primary winding 18 energized from source 27 by a magnetic core 16 movable by diaphragm 13 responsive to the pressure difference across a flow meter orifice 11 in a conduit. By reversing switches 30, 31 the D.C. meter is replaceable by a temperature-sensitive thermocouple 32 in the conduit in series with an adjustable balancing D.C. source 33, while the output of windings 19, 20 is replaced by the armature winding of a phase-responsive A.C. meter 35 having a field winding energized by source 27. In the first switch position an A.C. signal input from windings 19, 20, dependent in magnitude and phase on the magnitude and direction of deviations of fluid flow from normal is superimposed upon the rectifier bridge excitation to asymmetrically vary the rectifier resistances so that a direct current signal is developed across meter 12, which may be calibrated to indicate flow deviations. On reversal of the switches, a direct voltage dependent in magnitude and sign on the deviation of the thermocouple temperature from a present value is applied to the rectifier network' second diagonal and asymmetrically varies the rectifier resistances to apply an alternating signal voltage dependent in amplitude and phase on the magnitude and sign of temperature variations to the phase-responsive meter, which may be temperature calibrated. Fig. 3 shows an application to power measurement in which one rectifier network diagonal is excited from tappings on an impedance 221 shunting the line 38, and the other diagonal is connected to a D.C. meter calibrated in watts. The output of a current transformer 40 is connected between one side of the meter diagonal, and the tapping 23<1> on the shunt impedance, which may be in series with a voltage regulator 41, so that the meter reads the power component of the line current. In Fig. 4 (not shown), the invention is applied to the synchronization of two A.C. sources, one of which feeds the shunt impedance having taps connected to opposite points of the bridge rectifier, while the other is connected between the mid-point tap and the meter diagonal. In Fig. 5 (not shown), the invention is applied to indicate the measurements of a magnetic gauging bridge embodying dimensionallyvariable reactors, which is fed from the A.C. supply of the modulator, to which the gauging bridge output is applied. The meter is calibrated in terms of the measurement, or may be adjusted to zero by the shunt impedance tapping which is then calibrated. In Fig. 6 (not shown), the shunt impedance is replaced by the gauging reactors. Specifications 566,227, 579,299 and 13531/45, [as open to inspection under Sect. 91], are referred to.