. Electrical world. ective signalling system now standard with the Bell companies,the primary object being to overcome certain deleterious effects ofearth potentials. In the system as previously adopted, a relay con-trolling by its contacts the bell circuit, is bridged across the lineat each station, a condenser having first been introduced into itscircuit. The various bells, sensitive respectively to either positiveor negative impulses alone, are then connected through the relaycontacts from the line to ground, one bell of each kind being usedfor each side of the line, or four in all. Now, wh
. Electrical world. ective signalling system now standard with the Bell companies,the primary object being to overcome certain deleterious effects ofearth potentials. In the system as previously adopted, a relay con-trolling by its contacts the bell circuit, is bridged across the lineat each station, a condenser having first been introduced into itscircuit. The various bells, sensitive respectively to either positiveor negative impulses alone, are then connected through the relaycontacts from the line to ground, one bell of each kind being usedfor each side of the line, or four in all. Now, when considerableand variable potential differences exist between the various stationbell grounds, at times the direct currents in consequence thereofflowing through the bells will completely overpower the selectivesignalling currents and either cause failure of action or false Strykers scheme for overcoming the defect is shown diagram-matically in Fig. 2. It will be at once seen that the relative position. FIG. 2.—STRYKER SELECTIVE SIGNAL SYSTEM. of bell and the relay and condenser, have been changed, the relaycircuit alone being grounded. As the relays at all stations mustoperate on both impulse currents, whether positive or negative, thepresence of a condenser in the relay circuits is of no effect, exceptto overcome entirely the flow of direct currents due to earth poten-tials. The bell-controlling relays may be any one of several specialtypes which have been heretofore described in these columns. TheAmerican Telephone & Telegraph Company has been assigned thepatent for this system. A second system is that of Messrs. N. S. McKinsey and A. , of Susanville, Cal. This is what might be called an auto-matic step-by-step system, for all the various operations of selectingand calling a desired subscriber follow automatically the naturalevents of instituting a connection. Thus, the removal of a calling sub-scribers telephone from the switch-hook at once so manipu
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
