32 BIllJ. SYSTEM I ECIISICAL JOVRXAL 



Till' powtr for flevating and restoring the brush rod is providi-d 

 1)\ c()iiiiiiii(ni>l\ re\()l\ing motor dri\-cn steel rolls co\ered with cork 

 and nioimli'd ai liu- base of the frame. The dri\ing of the brush rod. 

 the tripping of llie desired brush, the stopping of the rod and its 

 restoration to normal are all controlled by a series of electro-magneis 

 assembled in a single structure called a clutch which is also moinited 

 ai the liaM' of tlu' frame directl}- in front of the rolls. When a brush 

 rod i^ drivin litlier up or down, a clutch armature establishes a fric- 

 tion contact between a flat strip of phf)sphor bronze fastened to the 

 lower end of the brush rod and the cork on the revolving rolls. This 

 clutch is comparable to an indisidual rela\' structure with a mul- 

 tiplicity of windings and armatures ihat are .so related that e.uli 

 arnialiire will operate oiiK when its .issnciaied winding is energized. 

 The liutrli tlui^ does the \\(irk of eilher an exceedingly intricate' 

 indi\idual rela>- or a whole group ot less comjilicated rela\s. The 

 clutch windings arc in effect, relay windings that control the posi- 

 tions of remote contact springs through the operation of armatures 

 wliiili a.ssociate or disassociate electro-magnetic and mechanical 

 energy as is desired. 



Tiih; Stici'-uv-.Stiu' .Sia.i-x tor 



.\noiher t>|)e of multi-contact relay in general use that differs in 

 form from both the secjuence switch and the power drixen selector 

 i> the step-by-step selector shown in I'ig. '_'H. It tdii>ists of six semi- 

 circular contact le\-els assembled in .1 b.ink .md an electro-magnet 

 which dri\-es a set of six, double eiuKd. rotar\ bnishes oxer the ter- 

 minal arc by means of a dri\ing pawl and ratchet wheel. Kach time 

 the magnet is energized and released the driving pawl engages the 

 next tooth on llu- r.itcliet wheel which rotates to ad\-ance the brushes 

 a singU' ^tip so th.it tlux make contact with the next set of terminals. 

 In II successixe steps the six lirushes moxt' through a complete rexolu- 

 tioii but as they are double-ended all the possible circuit combina- 

 tions are set up in the first 22 steps and are then repeated. 



In this selector the winding of the electro-magnet corrtsponds to 

 the winding of an indixidu.il rel.ix'. The .irnLiture in oper.iting 

 elongates a si)ring that i> shown in I'ii;. 2:5 and the eiurg\ .sloieil in 

 this spring restores the arm.iture to normal and adxances the six 

 contact making brushes to the next set of contact terminals. Thus 

 the relay winding antl armature control the iiosition of the contact 

 springs through the agency of a flexible mechanical link. The rela\ 

 winding may be alternately energized anil reieasetl by current inter- 

 ruptions from an outside source or the armature may be arranged to 



