Cyclopedia of Telephony and Telegraphy, Vol. 1: A General Reference Work on Telephony, etc. etc.

By American School Correspondence

t will be noticed that the ringer and the relay coil 6 at the first station are

bridged across the sides of the line leading to the central office. In like

manner the bell and the relay magnets are bridged across the two limbs of

the line leading into each succeeding station, but this bridge at each of the

stations beyond Station A is ineffective because the line extension R_{x} is

open at the next station nearest the central office.

In order to ring Station A it is only necessary to send out ringing current

from the central office. This current is in such direction as not to cause the

operation of the relay, although it passes through the coil 6. If, on the other

hand, it is desired to ring Station B, a preliminary impulse would be sent

over the metallic circuit from the central office, which impulse would be of

such direction as to operate the relay at Station A, but not to operate the bell

at that station. The operation of the relay at Station A causes the spring 2

of this relay to engage the spring 3, thus extending the line on to the second

station. After the spring 2 at Station A has been forced into contact with

the 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 its

normal position, thus breaking the bridge circuit through the bell at that

3 AMERICAN SCHOOL OF CORRESPONDENCE

station. It is apparent now that the action of coil 6 at Station A has made

the relay powerless to perform any further action, and at the same time the

line has been extended on to the second station. A second similar impulse

from the central office will cause the relay at Station B to extend the line on

to Station C, and at the same time break the circuit through the operating

coil and the bell at Station B. In this way any station may be picked out by

sending the proper number of impulses to operate the line relays of all the

stations between the station desired and the central office, and having picked

out a station it is only necessary to send out ringing current, which current

is in such direction as to ring the bell but not to operate the relay magnet at

that station.

In Fig. 197, a four-station line, such as is shown in Fig. 196, is illustrated, but

the condition shown in this is that existing when two preliminary impulses

have been sent over the line, which caused the line relays at Station A and

Station B to be operated. The bell at Station C is, therefore, the only one

susceptible to ringing current from the central office.

Since only one bell and one relay are in circuit at any one time, it is obvious

that 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 large

number of bells as in the bridging system of operating step-by-step devices,

which method sometimes so greatly reduces the effective current for each

bell that it is with great difficulty made to respond. All the energy available

is 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 of

the various pieces of apparatus may be made with less delicacy than is re-

quired where many pieces of apparatus, each having considerable work to

do, must necessarily be operated in multiple.

The method of unlatching the relays has been briefly referred to. After a

• Format: Paperback
• Language: English
• ISBN: B0HGTQHVVX
• ISBN13: 9798240879821
• Release Date: August 2026
• Publisher: Katrinabooks
• Length: 114 Pages
• Weight: 0.36 lbs.
• Dimensions: 9.0" x 0.2" x 6.0"