Patent GB-503829-A (GB)
Title: Improvements in or relating to the correlated adjustment of resistances, capacities and inductances in electric circuits
IPC: G01R1/30
Filed: 1937-07-07
Abstract: 503,829. Electric tests; resistances ; regulating switches. CAIN, R. July 7, 1937, No. 18908. Convention date, July 7, 1936, [Class 37] [Also in Group XXXVII] The invention relates to an electrical device comprising terminals A, B, Fig. 3, between which a circuit containing two impedances X, Y (resistance, capacity, or air-cored inductance) are connected, and wherein, when one impedance is varied, for example, to alter the sensitivity of a meter G, the other impedance is automatically varied to maintain the total impedance between the terminals A, B constant. According to the invention, the two impedances X, Y or terminals connected to tappings thereof, are mounted on one support and the wiper contacts 1<SP>1</SP>, 2<SP>1</SP> therefor on a second support; the impedance of each element varies rectilinearly with the number of tappings thereof switched in or out, and the relative movement of the two supports is so constrained that the ratio of the rate of switching in or out of the respective impedances is variable throughout the range of relative movement of the supports. Figs. 4 to 12 (not shown) show other circuit arrangements of the impedances X, Y, for varying the sensitivity of a meter G. In Fig. 13, the impedances X, Y serve, with a constant applied voltage, to vary the current passing through a capacitance C although the capacitance between the terminals A, B is kept constant. The device may also be used, Fig. 27, to give a variable voltage between the terminals A, B from a source U with constant resistance between the terminals. Fig. 15 shows resistances X, Y, engaged by wipers 15, 16, respectively, carried by rods 13, 14, slidable in a head 9 which moves along a guide 10 corresponding in shape to the law connecting the resistance values x, y to maintain the total resistance constant. When this law is of the form x.y = a constant, use is made of the geometrical property of the circle illustrated in Fig. 17 where for any position of the line O 1 L 1 , OtKi x O 1 L 1 =a a constant = (O 1 O 3  )<SP>2</SP>- R K 2 or for a point O 2  inside the circle O 2 L 2  x O 2 K 2  = a constant = RK<SP>2</SP> - (O 2 O 3 )<SP>2</SP>. Thus, Fig. 20 shows two resistances X, Y mounted on straight parallel arms 24, 25 extending radially from a rotatable shaft 26, the relatively movable contacts 11, 21 co-operating, respectively, with X and Y, being arcuate in shape, Figs. 18, 19 (not shown), and carried on plates 19, 20, urged apart by springs 27 and carried by a bracket 23. Insulating pieces 29, 30 are provided between the ends of the arcuate contacts 1<SP>1</SP>, 21 to form a complete circle, Figs. 18, 19 (not shown). Figs. 21-23 (not shown) show an arrangement similar to Fig. 20 but wherein the axis 26 is inside the circle formed by the contacts 1<SP>1</SP>, 21, and in which the resistance carrying parallel arms 24, 25 are on opposite sides of the axis 26. In a further construction the resistances X, Y, Fig. 25, on the parallel arms 24, 25 rotate about an axis 26 outside the circle formed by the arcuate contacts 32, 33, mounted in slots in a fixed insulator 31, and are connected thereto by balls 34, 37 connected by forks to contact rollers 36, 39. Alternatively, terminals only connected to tappings on the resistances X, Y may be mounted on the arms 24, 25 and fixed series resistances Xo, Yo may be provided. Fig. 26 shows how the invention may be applied to a temperature indicating device for a furnace. A1, B1 and A2, B2 are the terminals of two devices according to the invention. A standard cell 42 is first connected in series with A1, B1 and the E.M.F. thereof balanced against the potential drop across the portion 43 of resistance X2 by moving the wiper contact 50 of rheostat 49, this adjustment being effected automatically in known manner by the meter 46 connected in the circuit A, B. The switch 45 is then thrown into its lower position to connect a thermo-couple 41 in series with the circuit A1, B1. The meter 46 is then arranged automatically to balance the potential drop across the portion 43 against the em.f. of the couple 41 by operating the wipers 1<SP>1</SP>, 2<SP>1</SP> of resistances X2, Y2, the temperature being indicated by a galvanometer 51 which may serve to regulate the temperature. The Specification as open to inspection under Sect. 91 comprises also the following subjectmatter. Fig. 12 (Cancelled) shows the resistance X tapped in fairly large steps, the resistance Y having coarse and fine sections Y<SP>1</SP>, Y<SP>11</SP>, each provided with a sliding contact 2<SP>1</SP>, 3<SP>1</SP>. Figs. 16, 17 (Cancelled) (not shown), show the resistances X, Y mounted on arcuate arms, tappings thereof being connected. to switch contacts co-operating with a diametral rotary arm. Ammeters and voltmeters provided with a variable shunt or series resistance, as the case may be, may be connected in circuit with impedances X, Y according to the invention to increase their sensitivity ranges. A frequency meter may be rendered independent of changes in voltage by means of a pair of impedances according to the invention. This subject-matter does not appear in the Specifica. tion as accepted.