Cyclopedia of Telephony and Telegraphy, Vol. 1 (Paperback)

Paperback. t will be noticed that the ringer and the relay coil 6 at the first station arebridged across the sides of the line leading to the central office. In likemanner the bell and the relay magnets are bridged across the two limbs ofthe line leading into each succeeding station, but this bridge at each of thestations beyond Station A is ineffective because the line extension R_{x} isopen at the next station nearest the central office.In order to ring Station A it is only necessary to send out ringing currentfrom the central office. This current is in such direction as not to cause theoperation of the relay, although it passes through the coil 6. If, on the otherhand, it is desired to ring Station B, a preliminary impulse would be sentover the metallic circuit from the central office, which impulse would be ofsuch direction as to operate the relay at Station A, but not to operate the bellat that station. The operation of the relay at Station A causes the spring 2of this relay to engage the spring 3, thus extending the line on to the secondstation. After the spring 2 at Station A has been forced into contact withthe spring 3, it is caught by the latch of the spring 5 and held mechanically.When the impulse from the central office ceases, the spring 1 resumes itsnormal position, thus breaking the bridge circuit through the bell at that3 AMERICAN SCHOOL OF CORRESPONDENCEstation. It is apparent now that the action of coil 6 at Station A has madethe relay powerless to perform any further action, and at the same time theline has been extended on to the second station. A second similar impulsefrom the central office will cause the relay at Station B to extend the line onto Station C, and at the same time break the circuit through the operatingcoil and the bell at Station B. In this way any station may be picked out bysending the proper number of impulses to operate the line relays of all thestations between the station desired and the central office, and having pickedout a station it is only necessary to send out ringing current, which currentis in such direction as to ring the bell but not to operate the relay magnet atthat station.In Fig. 197, a four-station line, such as is shown in Fig. 196, is illustrated, butthe condition shown in this is that existing when two preliminary impulseshave been sent over the line, which caused the line relays at Station A andStation B to be operated. The bell at Station C is, therefore, the only onesusceptible to ringing current from the central office.Since only one bell and one relay are in circuit at any one time, it is obviousthat all of the current that passes over the line is effective in operating a sin-gle bell or relay only. There is no splitting up of the current among a largenumber of bells as in the bridging system of operating step-by-step devices, which method sometimes so greatly reduces the effective current for eachbell that it is with great difficulty made to respond. All the energy availableis applied directly to the piece of apparatus at the time it is being operated.This has a tendency toward greater surety of action, and the adjustment ofthe various pieces of apparatus may be made with less delicacy than is re-quired where many pieces of apparatus, each having considerable work todo, must necessarily be operated in multiple.The method of unlatching the relays has been briefly referred to. After a Explore the intricate mechanics of early telecommunications through a deep dive into the electrical impulses and relay systems Shipping may be from multiple locations in the US or from the UK, depending on stock availability.…