GB591141A - Improvements relating to electrical measuring and calculating apparatus - Google Patents

Abstract

591,141. Current and voltage measurements. COSSOR, Ltd., A. C., BEDFORD, L. H., and JOFEH, L. June 7, 1944, No. 10933. [Class 37] In a circuit arrangement for the study of the rate of change of a variable quantity, an alternating voltage of constant frequency is amplitude-modulated in accordance with the variable quantity and combined with a timedelayed cophased copy of itself to produce a resultant wave modulated in accordance with the desired rate' of change. In one arrangement, the modulated voltage V1 is applied to an artificial line L1, L2, L3, C1, C2, Fig. 1, terminating in a resistance R0 equal to the characteristic impedance of the line. The voltage V2 across the resistance R0 is a timedelayed copy of V1 on a reduced scale and is combined with V1 similarly reduced by a potentiometer Rl to give the desired voltage V3 which may be taken off from a tuned transformer T1. The time-lag of the artificial line is arranged to be a complete number of cycles of the input carrier voltage so that the waves V1, V2 are co-phased. Alternatively, the time lag may be an odd number of half periods of the carrier if a phase inverting mechanism is used. The voltage V3 may be reproduced as a voltage to earth as described in Specification 582,018, [Group XL]. In another arrangement, the delayed voltage V2, Fig. 2, is taken from the terminals of a tuned circuit LC1 connected across the input V1 in series with a resistance R2 of large ohmic value compared with the impedance of LC1. V2 is again combined at V3 with a correspondingly reduced portion of V1 taken off a potentiometer R1. The voltage V2 across the tuned circuit LC1 may, alternatively, Fig. 3 (not shown), be compared with a voltage on the same reduced scale developed across another tuned circuit of lower Q, i.e. two time-delayed versions of V1 having different time lags, are compared to produce V3. The resistances, e.g. R2 of Figs. 2, 3 in series with the tuned circuits may comprise a thermionic valve, Fig. 4 (not shown). In a further modification, particularly suitable for low frequencies, e.g. 50 cycles, the modulated voltage V1, Fig. 5, is applied through a transformer T2 to the input of a resistance-capacity coupled amplifier P1, P2. The anode load of pentode P2 comprises series connected condenser C4, resistor R4 and (in parallel) resistor R5 and condenser C5. The voltage V2 which is a delayed version of VI, is developed across the parallel combination R5, C5 and is fed back degeneratively through tapping 14 to the' input of P1, so that V3 the resultant of V1, V2 appears across terminals 15, E. Initially, with VI cut off, the amplifier is set into self-oscillation by reducing one of the cathode load resistors, e.g. R7, when it functions as a known type of oscillator. The oscillation frequency is then adjusted, by varying one or more of the anode circuit components of P2, until equal to the frequency of V1. The resistor R7 is then adjusted until oscillation ceases, and with V1 applied to the amplifier the tapping 14 is adjusted to vary the relative proportions of the instantaneous and delayed versions of VI. Instead of reducing the voltage V1 to the scale of V2, the latter may be amplified up to the scale of V1.