Patent GB-992641-A (GB)
Title: Improvements in or relating to measuring device
Inventor: COHEN ALEXANDER ELYAKUM ZUNDEL
IPC: G05D3/14
Filed: 1962-01-05
Abstract: 992, 641. Transmission and phase angle measurements. GENERAL ELECTRIC CO. Ltd. Jan. 4,1963 [Jan. 5, 1962], No. 511/62. Heading G1U. Measuring device indicating a component of the transfer ratio of a linear transmission system comprises a measuring instrument indicating the algebraic mean of the current therein, means applying a sinusoidally amplitude modulated voltage to the system under test, and means applying the output voltage thereof over a switching arrangement to the instrument; the switching operating independence on a reference voltage corresponding to the modulated voltage so that the current in the instrument is in one or the other sense according as the reference and modulated voltages are of the same or opposed polarity; the arrangement being such that the instrument measures the component of modulation frequency in the output of the system at a phase angle with respect to the component of modulation frequency in the input to the system which is equal to the phase difference between the modulation component in the reference voltage and that in the modulated voltage, and so indicates the corresponding component of the system transfer ratio. In Fig. 1 a magslip 1 with a single wound rotor and a triple wound 120 degrees star stator is driven by a D.C. motor 2 energized through a speed control 3 from a 400 c.p.s. supply also energizing the rotor, to produce a 400 c.p.s. carrier modulated by a frequency set by the drive speed, which is measured by tachometer generator 4 and voltmeter 5, and the stator output excites the stator of a further magslip 6 whose rotor is angularly adjustable by scale 9 to energize regulating potentiometer 7 to produce a voltage E i  whose amplitude is varied by the potentiometer setting and the phase angle of whose modulation is varied by the rotor setting,applied to a linear transmission system 8 whose output E o  is applicable alternately with amplifier 14, and halfwave rectifier 30 to measuring inputs 11, 12; each of which comprises a microammeter 15 and a transistered switching unit 18, arranged to connect the rectifier output in opposed senses through the meters on opposite halfcycles of control voltages E s  = — sin w m t sin w c t and E c  = — cos w m t sin w c t in quadrature therewith respectively derived between two outputs of the stator of magslip 1 and between the remaining output and the centrepoint of potentiometer 25, 26 across the two outputs; where w m /2# is the modulating frequency set by the speed of motor 2 and w c /2# is the carrier frequency of 400 c.p.s. The halfcycles of the modulated signal output E o  of network 8 which are in and out of phase with the control voltage E s  produce rectified currents in opposite senses in the meter of unit 11 (Fig. 2 not shown) and the mean current therein is given by E o cos #. Initially E i  is connected directly by switch 10 to attenuator 13 and with control 9 at zero potentiometer 7 is adjusted for unity reading. Network 8 is then introduced, and the meter reading represents the in-phase component of the transfer ratio thereof. Similarly the mean current in the meter of unit 12 is given by E o  sin #, so that the reading thereof indicates the quadrature component of the transfer ratio. Control 9 may alternatively be adjusted for null quadrature response, and the meter of unit 11 indicates amplitude and control 9 the phase angle of the network output.