Patent GB-491898-A (GB)
Title: Improvements in and relating to devices for measuring and testing electric resistances
IPC: G01R27/02
Filed: 1937-03-16
Abstract: 491,898. Resistance measurements. ELEKTRISCHE GLUHLAMPENFABRIKEN J. KREMENEZKY AKT.-GES. March 16, 1937, No. 7723. Convention date, March 19, 1936. [Class 37] The resistance value from one end of a resistance to a point varying along its length is read or checked continuously by the pointer of a resistance measuring instrument which plays over a chart moved according to the relative movement of the resistance and the contact member feeling along it. As shown, the resistance 3, Fig. 1, comprises an annular segmental sheet applied to an insulation backing and mounted at 2 concentrically on a shaft 1. The ends of the resistance are connected to studs 4, 5 to which current is led by brushes 8, 9, and slip rings 6, 7, a fixed contact 10 bearing on the resistance as it is rotated with the shaft 1 by a handle H. Driven from the shaft 1 is a spindle 11 carrying a drum 12 on which interchangeable charts C may be mounted, each chart, Fig. 3, carrying a series of families of curves a<1>, a, a<2> ; b<1>, b, b<2> ; c<1>, c, c<2>, &c. The families of curves correspond to different ranges of the measuring instrument, the pointer 15 of which should follow the curve a and then b as the shaft 1 is rotated to cause the pointer to indicate the resistance between one end (brush 8) and the contact 10 of the resistance 3, the measuring instrument being switched over from one range to another automatically as hereinafter described. The curves a, b show the desired resistance values, the curves a', b1 and a<2>, b<2> showing the upper and lower permissible tolerance values, respectively. The curves c<1>, c, c<2>, correspond to the total resistance 3 between brushes 8, 9. Resistance measurement. The measuring instrument I, Fig. 2, is a current-responsive meter connected in series with the resistance 3 under test and with a fixed but adjustable resistance, depending upon the range, across a 4-volt or 220-volt supply which also depends on the ranger. Three ranges are provided for, the connections to the + 4 or + 220 volt terminal and the required series resistances We<1>, W<1>, We<2>, W<2>, We<3>, W<3>, and shunt resistances Ws<1>, Ws<2> being controlled by relays R<1>, R<2>, R<3> for the respective ranges. A further range may be provided by the use of a double pole switch S. A plug-board T permits the automatic use of any of the three ranges. Thus, in the present instance, since only two ranges are required plugs are inserted as shown so that only relays R<1>, R<3>, are successively energized across a supply S<4> as a contact arm 16 is driven over contacts 17 ... 22 by the shaft 11 of the chart drum, whereby the instrument I is automatically switched over from the range corresponding to R<1> to that corresponding to R3 as the contact arm 16 passes from contact 19 to 20, so that the tip of pointer 15 traverses curves a and b successively. A switch 40 short circuits the test resistance 3 for zero adjustment of the instrument I and a switch U<2> in its two positions enables the test resistance to be checked from end 8 or end 9. The range control relays R<1>, R<2>, R<3>, are energized over a switch U<1>, which, when thrown to its other position, energizes a relay R<4> which connects the whole of resistance 3 in the measuring circuit. The total resistance indicated by curves c<1>, c, c<2> may therefore be traversely by the tip of pointer 15, Fig. 1, the range of the instrument being altered in this case by manual operation of a switch U<3>. More than three ranges may be provided for. Resistance correction. The resistances 3 are normally manufactured so that they fall below the lower tolerance values indicated by curves a<2>, b<2>, &c. a grinding and polishing device 38, 39, Fig. 1, independently driven, being applied to a resistance 3 while at rest during the test, to reduce its dimensions and thereby increase its resistance until the pointer tip always lies within the tolerance curves.