Marvels of Automatic Telephone Exchanges —Machines That Work With Super-Human

Sun (Auckland), Volume II, Issue 532, 8 December 1928, Page 17

Marvels of Automatic Telephone Exchanges —Machines That Work With Super-Human

(Written for THE SUN

by

O. A. GILLESPIE.)

P

ROGRESS has brushed aside the telephone girl. Irate subscribers no longer hurl abuse through the telephone at poor defenceless attendants. Progress has obligingly brushed that aside, also. An insistent drumming in the .ears tells the subscriber that his number is engaged. All the abuse in the world has no effect on an automatic telephone—except to break it. When the first telephone exchange was opened in Auckland in 1881 a few timid subscribers were delighted with the advance of civilisation. Now there are 17,460 odd subscribers using the telephone daily and many others whose days of waiting for an installation are nearly over. Extensions to the various telephone exchanges in the City of Auckland, when completed, will bring the number up to 23,000, though these will not all find owners for some time to come. The proud owner of No. 1 on the first telephone exchange in Auckland was the firm of Fraser and Tinney. Under the automatic system individual numbers have been done away with and each is now prefaced with initial figures which range from 12 to 47. The old Post Office in Shortland Street, a quaint and attractive example of architecture which is still standing, did duty for many years as both post office and telephone exchange. At first a few slender wires connected the subscribers to the exchange, but as the telephone became more popular, a forest of poles gradually appeared in the streets of Auckland. More subscribers meant more lines, and soon the street-poles were festooned with hundreds of wires which swung in every wind and howled in every gale. Periodically they developed faults and the irate subscribers became still more irate. Twenty-five and thirty years *go giant totara trees growing at Matapouri and Ngunguru, north of Vfhangarei, and at Whangaroa and Totara North were felled and brought 1° the city to carry the immense and steadily-growing festoons of telephone wires. Huge things they were. Some of them are still standing in Queen Street and other parts of the tity, but very few. Progress is Crushing them aside also.

Only last Wednesday one of the largest of these “forest giants” was felled in Shortland Street. For 25 years it had carried the thousands of wires and cables from the whole of Auckland into the old Shortland Street office. It was familiarly known as the "office pole” by officials of the Post and Telegraph Department. Standing 45ft high, this heart of totara was as sound on Wednesday as the day it was felled in the forests of North Auckland. It was 2ft. square at the base and was embedded to a depth of 10ft. in concrete to withstand the enormous strain of the weight of wire. Five years ago the city streets, and Queen Street in particular, were an unsightly tangle of overhead wires. But progress has done away with all this. Someone invented the automatic telephone and decided that all the

telephone wires could be decently and artistically hidden underneath the footpath. Soon busy workmen were rooting up miles of footpath and street intersections; others were building a new

telephone exchange in Wellesley Street and smaller ones in the suburbs. People still went on using their manual telephones and answering the “Hello” girls in the exchange. But the change was coming. One morning, about four years ago, Auckland woke to find itself using the automatic telephone. Five exchanges were cut over at midnight and the manual telephone, for the majority of subscribers, was a thing of the past. This cut over, by the way, was the biggest which has ever taken place in the world and was complete in every detail. While the new service was being installed the old service had been maintained in perfect order; in one minute the change was made from manual to automatic. And still progress brushes our once up-to-date methods aside. Soon the whole telephone service of the Dominion will be revolutionised by

the introduction of the “carrier” system of telephony. This new system is really a method of wireless communication in which electric waves, instead of being broadcast, are directed over the telephone wires, thus making communication much clearer. Before many years are out we will be talking as easily over the wire to people in Invercargill and other centres of the South Island as we do now to friends in the suburbs. At present, however, the automatic telephone is our main concern. How many people stop to think, when they lift their receivers and nimbly twirl the dial, of the delicate and intricate mechanism they are putting into motion? It is a marvellous invention and could almost be compared to a mechanical brain. A visit to an automatic exchange leaves one more appreciative of the useful telephone and staggered that such intricate machinery can work so accurately. Its precision is uncanny. Compared with the old exchange the new is amazingly quiet. No rows of girls, with receivers clamped uncomfortably to their ears, ceaselessly answering questions; no listening and plugging-in of connections, no bustle, no disturbance of any kind. Instead there is the quietly uncanny whirr of machinery which never stops, day or night. Every second or so there is the hiss, as of a spring being released suddenly. A few electricians and mechanics move about quietly on a polished floor, adjusting the mechanism, attending | to faults or just watching that everyI thing is in running order. The only [ girls are those who tend to toll calls.

The hiss is part of the mechanism returning to its place when two subscribers have finished speaking; the whirr, more like a loud and prolonged purr, is when the mechanical brain is searching out a number among the bewildering array of intricate machinery. _ There must be no dust in an automatic telephone exchange, as it would clog and injure the delicate mechanism. Consequently boots are carefully brushed before going in and doors are closed to prevent its appearance. All the mechanism is carefully dusted by attendants; the automatic must be treated with the greatest respect. Neither must the air be too moist. This is another matter which requires constant and careful attention. For this purpose there is a complete refrigerating plant installed in each exchange. This forms part of an airconditioning plant which functions to control the relative humidity and temperature of the exchange atmosphere and to provide dust-free air.

The presence of excess air moisture is fatal to the successful operation of the delicate electrical mechanism, and the insulation of the silk and cotton-covered wires used for inter-connecting the various pieces of equipment, must be maintained at a high value. Before being admitted to the exchange the air is first drawn through a -washing and cooling-chamber where it is chilled and freed from dust by contact with atomised water at a low temperature. The air is then raised in temperature by being passed over a series of radiators, finally entering the exchange through an elaborate system of ducts at a suitable temperature and relative humidity. Approximately 12,000 cubic feet of treated or conditioned air is supplied and exhausted every minute in the Wellesley Street exchange by means of two electrically-driven fans.

On entering the exchange in Wellesley Street one is impressed by row after row of substantial iron racks supporting an enormous number of moving switches. One observes, with wonder, the methodical precision of the revolving shafting and gears, the ceaseless clicking of the switch-brushes as they sweep over rows of terminals, and' the mass of cables and wiring. At first it is all terribly confusing, but there is an amazing order in this apparent confusion. The wires connecting the subscribers’ telephones with the exchange equipment are conveyed in leadsheathed cables of a size accommodating up to 1,000 pairs. These cables are led in from underground through a subway and up a shaft to the switch-room on the top floor, where they terminate on special protective apparatus supported on a series of iron frames. Here each individual pair of wires, comprising one

subscriber’s circuit, is consecutively numbered and connected to its own particular electro-magnet. From this point subscribers’ apparatus is arranged in groups, each group being common to a number of lines. Thus we have the group lines of 12 to 47 in Auckland. The wires inter-connecting the multitude of various pieces of exchange equipment are covered and insulated with enamel, silk and cotton. The outer cotton covering is distinctive in colour and serves as a means of identification when the cables are formed for the purpose of wiring. To preserve the insulation the cables are saturated in beeswax where they are opened for “forming,” and, after being neatly laced up, are soldered to the tens of thousands of terminals. The progress of a call through an automatic exchange appears bewildering to the casual onlooker because so many circuit ramifications are involved.

When the calling subscriber removes the receiver from the telephone switch-hook an electrical circuit is completed to the exchange, causing a small electro-magnet (technically known as a "relay”) to operate. This “relay” in turn starts a group of switches rotating to hunt for the calling line. These switches perform their duty with uncanny accuracy. When one of these “line finders,” as they are called, selects the wanted line, a second similar type-switch is rotated to link up with the first finder and the calling subscriber is connected to a group of switches known as “registers.” Dialing tone, or the familiar humming sound which tells that the line is all clear, is then heard. Now follows the selection of the wanted number. The registerswitches comprise seven separate units, two of which act as controllers and the remaining five each receive one set of current impulses corresponding with the digit operated from the dial of the calling telephone. These “registers” may be termed

the brains of the system, as they function to receive and translate the dial impulses and, if necessary, store up these impulses until circuit channels are available for the direction of the called number into the correct group of apparatus serving the wanted party’s line. Immediately the channels are available the registers unload their impulses into another type of switch, known as the group selector. The first group selector, having been properly set by the register, automatically rotates its brush carriage over a number of terminals to which are wired trunks or channels extending to sub-group selectors. These in turn, also under the control of the register, automatically select further sub-groups of channels to the final selectors, which are set in rotation, to step over groups of terminals to which the wanted line is connected. The register, having completed its work in directing the call through the proper channels, is now automatically restored to its normal position, and may be used to establish further calls. It may be stated that the register is occupied only during the building up of the circuit necessary to extend the calling party to the wanted party or for a period of from 10 to 12 seconds. The final selector, having stepped its brush carriage to the terminals of the wanted line, now tests to determine whether the line is free or engaged. If the line is free, circuits are immediately established to ring the wanted party’s telephone bell, but if the line is engaged the switch is held in the “busy” position, and the distinctive buzz-buzz of the engaged signal is transmitted back to the calling telephone. Immediately a call is answered by removing the receiver from the tele-phone-hook ringing is cut off and talking may take place. The restoration of the receiver to the switch-hook of both telephones causes the apparatus involved in the connection to return to normal and the mechanism is instantly ready to handle further calls from the same or other telephones. All this action takes only a few seconds to complete when one is using a telephone. The mechanism works so swiftly and accurately that users of the telephone cannot possibly imagine what happens (unless they have been through an exchange) every time they dial a number. As can be imagined the electrical and mechanical apparatus in an automatic telephone exchange is extremely intricate and requires delicate adjustment and skilled attention. Some idea of the extent of the plant which is housed in the Wellesley i Street exchange, with its equipment

for 7,600 working subscribers, can be gathered from the fact that there are 16,000 sets of protective appliances to render the equipment as immune as possible from damage due to lightning, power interference, etc.; 48,000 electro-magnets or “relays”; 10,500 switches of various types, many miles of connecting wires in cables, and something like 10,000,000 soldered electrical connections. In addition there is a vast array of shafting and gears, continuously rotating under power from 16 small commercial electric motors. Then there is a power plant consisting of two 45 h.p. motor generators for charging a set of large storage batteries, from which talking and operating current is supplied to all the lines connected with the exchange. Among this astonishing array of apparatus is a very complete arrangement of alarm circuits and indicators which automatically draws attention to apparatus failures. Hundreds of small electric lamps of different colours are used as visual indicators to announce that something is wrong

and for the purpose of assisting the staff to locate troubles. A large testing desk is equipped with modern appliances and enables the officers rapidly to test and locate outside line troubles which are bound to occur from time to time. Regular routine testing is systematically carried out, both of inside exchange equipment and subscribers’ line apparatus. Frequently incipient faults are discovered by these means and remedied

before the trouble is noticeable to the subscribers. The same conditions apply in each of the seven exchanges scattered throughout the city and suburbs. They, however, are on a smaller scale. Auckland's telephone system is growing by leaps and bounds and several of the exchanges are being enlarged to meet the constant demand of new subscribers. There are exchanges at present in Wellesley Street (the principal exchange), Remuera, Mount Eden, Ponsonby, Takapuna, Onehunga and Devonport. Although smaller in size, each exchange woiks exactly as its parent in Wellesley Street. The men who preside over this vast array of telephones and mechanism are Mr. E. C. Gage, chief telegraph engineer; Mr. A. Campbell, deputy-engineer, and Mr. W. E. Vivian, who has control of the automatic plant. There is a staff of between 30 and 40 highly-trained electrical engineers, mechanicians and lines*men to take care of the exchanges,

and every man is necessarily an expert. Approximately £1,000,000 is invested in Auckland’s telephones. Half of this is sunk in inside equipment and the other half lies under the streets in cables and wires. But the revenue derived from the , telephones is no small sum. Last year the telephone exchange revenue for the whole of the Dominion : amounted to £1,000,000.