Cyclopedia of Telephony and Telegraphy Volume Ii Part 25

It will also be seen that with this board it is possible to open any circuit merely by plugging into a jack. Two wires can be short-circuited or a loop made by plugging two cords of corresponding colors into the two jacks. A ground jack is provided for grounding any wire. In this way, a very flexible arrangement of circuits is obtained, and it is possible to make any of the simple tests which are all that are usually required on this type of circuit.

=Blocking Sets.= As was just mentioned, quite frequently in addition to train wires and message circuits, block wires are also operated by telephone. In some cases separate telephone instruments are used for the blocking service, but in others the same man handles all three circuits over the same telephone. The block wire is generally a converted telegraph wire between stations, usually of iron and usually grounded.

It seldom ranges in length over six miles.

[Ill.u.s.tration: Fig. 498. Blocking Set]

Where the block wires are operated as individual units with their own instruments, it is unnecessary to have any auxiliary apparatus to be used in connection with them. Where, however, they are operated as part of a system and the same telephone is used on these that is used on the train wire and message wire, additional apparatus, called a blocking set, is required. This blocking set, shown in Figs. 498 and 499, was developed especially for this service by the Western Electric Company.

As will be noted, a repeating coil at the top and a key on the front of the set are wired in connection with a pair of train wire cords. This repeating coil is for use in connecting a grounded circuit to a metallic circuit, as, for instance, connecting a block wire to the train wire, and is, of course, for the purpose of eliminating noise. Below the key are three combined jacks and signals. One block wire comes into each of these and a private line may be brought into the middle one. When the next block rings up, a visual signal is displayed which operates a bell in the office by means of a local circuit. The operator answers by plugging the telephone cord extending from the bottom of the set into the proper jack. This automatically restores the signal and stops the bell.

[Ill.u.s.tration: Fig. 499. Blocking Set]

Below these signals appear four jacks. One is wired across the train wire; one across the message wire; and the other two are bridged across the two pairs of patching cords on each side of the set. The operator answers a call on any circuit by plugging his telephone cord into the proper jack.

If a waystation is not kept open in the evening, or the operator leaves it for any reason and locks up, he can connect two blocks together by means of the block-wire cords. These are arranged simply for connecting two grounded circuits together and serve to join two adjacent blocks, thereby eliminating one station. A jack is wired across these cords, so that the waystation operator can listen in on the connection if he so desires.

In some cases not only are the telephone circuits brought into the test board, but also two telegraph wires are looped through this board before going to the peg switchboard. This is becoming quite a frequent practice and, in times of great emergency, enables patches to be made to the telegraph wires as well as to the telephone wires.

=Dispatching on Electric Railways.= As interurban electric railways are becoming more extended, and as their traffic is becoming heavier, they approximate more closely to steam methods of operation. It is not unusual for an electric railway to dispatch its cars exactly as in the case of a steam road. There is a tendency, however, in this cla.s.s of work, toward slightly different methods, and these will be briefly outlined.

On those electric railways where the traffic is not especially heavy, an ordinary magneto telephone line is frequently employed with standard magneto instruments. In some cases the telephone sets are placed in waiting rooms or booths along the line of the road. In other cases it is not feasible to locate the telephone indoors and then iron weather-proof sets, such as are shown in Figs. 484 and 485, are mounted directly on the poles along the line of railway. With a line of this character there is usually some central point from which orders are issued and the trainmen call this number when arriving at sidings or wherever they may need to do so.

Another method of installing a telephone system upon electric railways is as follows: Instead of instruments being mounted in booths or on poles along the line, portable telephone sets are carried on the cars and jacks are located at regular intervals along the right-of-way on the poles. The crew of the car wishing to get in touch with the central office or the dispatcher, plugs into one of these jacks and uses the portable telephone set. At indoor stations, in offices or buildings belonging to the railroad, the regular magneto sets may be employed, as in the first case outlined.

On electric railway systems where the traffic is heavy, the train or car movements may be handled by a dispatcher just as on the steam railroad.

There is usually one difference, however. On a steam road, the operators who give the train crews their orders and manipulate the semaph.o.r.e signals are located at regular intervals in the different waystations.

No such operators are usually found on electric railways, except, perhaps, at very important points, and, therefore, it is necessary for the dispatcher to be able to signal cars at any point and to get into communication with the crews of these cars. He does this by means of semaph.o.r.es operated by telephone selectors over the telephone line. The telephone circuit may be equipped with any number of selectors desired, and the dispatcher can operate any particular one without operating any other one on the circuit. Each selector, when operated, closes a pair of contacts. This completes a local circuit which throws the semaph.o.r.e arm to the "danger" position, at the same time giving the dispatcher a distinctive buzz in his ear, which informs him that the arm has actually moved to this position. He can get this signal only by the operation of the arm.

Each semaph.o.r.e is located adjacent to a telephone booth in which is also placed the restoring lever, by means of which the semaph.o.r.e is set in the "clear" position by the crew of the car which has been signaled. The wall-type telephone set is usually employed for this cla.s.s of service, but if desired, desk stands or any of the various transmitter arms may be used.

It is necessary for the crew of the car which first approaches a semaph.o.r.e set at "danger," to get out, communicate with the dispatcher, and restore the signal to the "clear" position. The dispatcher can not restore the signal. The signal is set only in order that the train crew may get into telephonic communication with the dispatcher, and in order to do this, it is necessary for them to go into the booth in any case.

[Footnote A: We wish particularly to acknowledge the courtesy of the Western Electric Company in their generous a.s.sistance in the preparation of this chapter.]

REVIEW QUESTIONS

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 11--68

1. What are the advantages of a common-battery system?

2. When is the local battery to be preferred to the common-battery?

3. Enumerate the different kinds of line signals.

4. Make a diagram of the arrangement of a direct line lamp signal.

5. What is a direct line lamp with ballast? Give sketch.

6. Describe a line lamp with relay.

7. What is a pilot lamp and what are its functions?

8. Sketch three different kinds of batteries applied to cord circuits.

9. What is a supervisory signal?

10. Make diagram of a complete simple common-battery switchboard circuit.

11. When will the supervisory signal become operative?

12. What is the candle-power of incandescent lamps used for line and supervisory signals?

13. At what voltages do they operate?

14. What are visual signals?

15. Describe the mechanical signal of the Western Electric Company.

16. Give a short description of the general a.s.sembly of the parts of a simple common-battery switchboard.

17. What is a transfer switchboard?

18. Outline the limitations of a simple switchboard.

19. Describe and sketch a plug-ended transfer line.

20. Why is the plug-seat switch not more widely adopted for use?

21. Make diagram of an order-wire arrangement.

22. What are the limitations of the transfer system?

23. What are the fundamental features of the multiple switchboard?

24. What is a multiple jack?

25. What is an answering jack?

26. Make a diagram showing the principle of multiple switchboards.