. American telephone practice . COMMON BATTERY SYSTEMS. 291 becomes necessary to economize in current as much as possible,electro-mechanical signals are used, these taking their place in thecircuit in the same relation as that usually occupied by the line orsupervisory relays, where lamp signals are used. An electro-mechanical signal of this type is that used by the Kel-logg Company, shown in Fig. 246, and commonly termed the grid-iron signal. In this a small aluminum target, marked on its facewith alternate black and white strips about one-eighth of an inchwide, is attached to the armature le
. American telephone practice . COMMON BATTERY SYSTEMS. 291 becomes necessary to economize in current as much as possible,electro-mechanical signals are used, these taking their place in thecircuit in the same relation as that usually occupied by the line orsupervisory relays, where lamp signals are used. An electro-mechanical signal of this type is that used by the Kel-logg Company, shown in Fig. 246, and commonly termed the grid-iron signal. In this a small aluminum target, marked on its facewith alternate black and white strips about one-eighth of an inchwide, is attached to the armature lever in such manner as to bemoved in its vertical direction by the attraction of the armaturethrough a distance just equal to the width of one of the black orwhite strips. Directly in front of the target is placed a black strip,having cut in it four horizontal slots equal in width to the width ofthe strips on the target, and equal in length to the width of the tar-get. When the magnet is de-energized the relative position of the. FIG. 246.—GRIDIRON SIGNAL. target with respect to the front strip is such that the black strips onthe target come directly in front of the openings in the front strip,thus presenting a continuous black surface to the eye of the oper-ator. When, however, the armature of the signal is attracted, thetarget is raised slightly so that the white strips come in front of theopenings in the front strip, thus displaying four white horizontalpatches where before all was black. The object of this gridironarrangement is to secure the display of a white surface of consider-able size with a relatively small movement of the armature andtarget. Another form of signal during the past few years has been quiteextensively applied by the Western Electric Company. This isshown in Fig. 247. In this the core of the magnet is clamped bymeans of a screw, a, to the mounting strip. Field between the coreand the mounting strip is a U-shaped pole-piece, c\ in which to pivot 292 AME
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