Patent GB-1072843-A (GB)
Title: Resistance switching assembly
IPC: H01C10/50
Filed: 1963-09-12
Abstract: 1,072,843. Electric meters. P. LUGER. Sept. 12, 1963 [July 26, 1963], No. 31204/63. Heading G1Q. [Also in Divisions H2 and H3] Potentiometers, skip potentiometers and resistance boxes, which may be used in multirange meters, particularly voltmeters, are described. The potentiometer of Fig. 1 comprises stages 1-4 each comprising a single resistor of the value shown and a double-pole, double-throw switch 13. The last stage comprises, in addition to the fixed 100K resistor, a potentiometer 19 of range equal to 100K. Considering the input to be applied across terminals 11, 12 of stage 1, if all the switches are in the "up" position, all the resistors are in circuit and all the fixed resistors are connected in series between terminal 11 ("in") and one end of the potentiometer 19, the other end of the potentiometer being connected through zero resistance to the "out" terminal 12. By throwing the switch in stage 1 to the lower position, the position of the potentiometer in the series is reversed, i.e. it is now connected through zero resistance to the "in" terminal and through all the fixed resistors in series to the "out" terminal. By suitable manipulation of the switches the potentiometer may be adjusted to any position in a series of sixteen resistances each of 100K value. In addition, by means of a further switch 20, the input may be applied, through further resistors having the values indicated, to those terminals of any of stages 2, 3, 4 corresponding to terminals 11, 12 of stage 1. Thus, by manipulating the switch 20, the potentiometer can be arranged to cover ranges of 100K, 200K, 400K, 800K and 1600K, the nearest 100K position being selected by the switches 13 and the final resolution being performed by the slide potentiometer 19. The basic principles of the binary potentiometer of Fig. 1 may be applied to a decimal potentiometer by using ten rotary switches of the kind illustrated in Fig. 2 (not shown) in the circuit of Fig. 4 (not shown). Each switch comprises three terminals connected to three rings (34, 35, 36) on the rotor (32) of the switch. The rings each carry a series of radial contacts (37) so arranged that in any position of the switch two contacts are connected by a pool of mercury (33) lying in the bottom of the stator (30). The ten switches are all ganged together and arranged in pairs, connections being made from rings (34, 36) in one member of a pair respectively to rings (36, 34) in the other member. In Fig.4, the rings are represented by vertical lines, the radial contacts by short horizontal lines and the mercury pools by circles. Resistors of the value shown and short-circuits interconnect the pairs of switches and the final pair is connected to a potentiometer (51). The switch rotors move in unison through ten positions and, as shown, are in position (5) where the slide potentiometer is connected in the IN terminal by a total resistance of 5 ohms and to the out terminal by a total resistance of 4 ohms. The circuit thus constitutes a decade divider adjustable in steps of one ohm with a slide for fractions of an ohm. It may be connected in a cascade of similar dividers using steps of 10, 100, 1000, etc. The separate decades in the cascade may be tapped to a switch through fixed resistances in such a manner that fixed resistances can be connected in circuit in the manner shown in Fig. 1. A further form of the potentiometer is described Fig. 8 (not shown) in which the commutator switches are of the slide variety the slides being driven by a series of cams on a common shaft.