GB244596A - Improvements in inductances and auxiliary apparatus for electrical measurements - Google Patents

Abstract

244,596. Campbell, A. Jan. 3, 1925. Inductances, measuring. - Relates to a mutual inductometer for electrical measurements in which a continuously-variable part has a normally fixed primary coil with a secondary coil mounted to be rotatable about an axis parallel to the mean plane of the fixed coil, the position of the axis being specially arranged to give an extended scale of mutual inductance. An arrangement whereby the scale opens very considerably towards the zero reading of mutual inductance and is of large angular extent is shown in Fig 2, wherein C is the normally fixed primary coil and D the secondary coil fixed to the vertical axle E, or, alternatively, D may be fixed and C rotated. Fig. 3 shows an arrangement for specially wellproportioned scale, one or more auxiliary coils F, G being fixed to the coil D and connected in series with it. Their function is to make the scale move open or close at desired regions and similar coils may be associated with the coil C. To place the zero reading in any position of the scale, coils may be put in series with the secondary coil and fixed relatively to the primary so as to add or subtract the requisite amount of mutual inductance. In that part of the inductometer giving the higher readings, the coil sections may be constructed by stranding the wire, but where high purity of mutual inductance is required the sections of the primary and secondary coils are of pancake or other anticapacity type, successive sections of the secondary circuit being adjusted to have the desired inductance. For the final adjustment of these sections, their ends are brought out to insulating bobbins in the form of undercut sectors Q - - S, as shown in Fig. 1, a few turns only being wound thereon and having a low value of inductance. The outer faces P of the primary and secondary coils may each carry ten sectors, thus giving subdivision for two decade switch dials, for example 1's and 10's, or the higher reading sections only may be adjusted in this way, lower reading ones being adjusted by stranding. For extreme purity the inductometer may have two primary or secondary circuits oppositely wound, and the one giving least impurity may be employed. In such measurements as those of alternating potentials at various frequencies, the primary C is arranged in whole or in part to rotate about a horizontal diametral axis, the secondary scale readings being multiplied by a factor appropriate to the adjustment of the primary. A long range of variation of this factor is required and is obtained by stepping the greater part of the primary with only a small part of it, concentric with the main part, mounted on a horizontal axis so as to provide by turning a continuous adjustment between the smallest steps. The Specification describes the application of the inductometer to the measurement of electrical quantities measured by an alternating-current potentiometer.