GB513597A - Improvements in or relating to alternating current standard resistances - Google Patents

Abstract

513,597. Standard resistances. SULLIVAN, Ltd., H. W., and GRIFFITHS, W. H. F. April 14, 1938, No. 11492. [Class 37] The invention relates to A.C. standard resistances mounted within an electrostatic screen and wherein two methods of using the screen are adopted, namely: I. Connecting the low potential end of the resistance to the screen, II. Connecting the screen to earth and then arranging that the low potential end of the resistance is at earth potential but not joined electrically thereto. By using method II the capacitance from resistance to screen is eliminaated so that the residual inductance of the resistance is more positive than in method I. According to the invention, a two-way switch 8, Fig. A, is provided for connecting the low potential end of the resistance 3 to the screen 7 in one position thereof (method 1.) while in the other position thereof it disconnects the resistance from the screen (method II.) and connects a compensating condenser 9 or condensers across the resistance or one or more portions thereof, in order that the residual reactance of the resistance shall be approximately the same for both switch positions. Where the resistance is variable, e.g. in the form of decade resistance dials 11,-14, four separate switches or a fourpole-two-way switch a, b, c, d, Fig. B, is provided, which in the method II. position connects compensating condensers 21-24 across the respective resistance dials 11-14. In another embodiment, applicable to resistance dials; in each position 56-65 of the resistance dial arm 38, Fig. C, a corresponding compensating condenser 46-55 is inserted across the resistance provided the two-way switch e is in the position e<2> for method II. When a plurality of resistances are used some may be left uncompensated. The embodiments in Figs. B, C, may be combined, and the resistances may be variable by plugs.