Electromechanical Switches Pdf
Convinced that such selectors could be adapted to large switches, Mathies had his group resume work. These features combined to make the switch very adaptable, easy to modify for both new applications and the addition of peripherals for new features. The selector moved continuously rather than in steps, and the selectors establishing contact points could move a considerable distance.
Citation Originally, all telephone calls required the participation of an operator. More than ninety percent of local calls in New York City involved phones connected to different local exchanges. Betulander of Televerket, the Swedish postal, telegraph, and telephone administration, began working on an all relay switch. Hochheiser curated historical exhibits, completed oral histories with company executives, and studied every aspect of the history of the telephone in the United States.
Within a decade, such telephone exchanges, with many improvements along the way, were in operation in nearly every city in the United States. This meant that all selector frames were accessible to all of the phones, and after a call they were released for use on other calls. It, like the panel switch, had separate circuits for selection and connection.
That is, the pulses from the telephone dial would be translated into a different electromechanical code that could control a larger switching unit. Electromechanical Telephone-Switching. The application of Strowger switches, as well as panel, rotary, and crossbar switches, testing .pdf automated the telephone system. Also required was a device that would allow switches to recognize area codes and automatically determine whether a local or long distance call was being attempted.
In the United States, Western Electric continued development of the panel switch, which was better suited for large cities with large volumes of interoffice calls. Blauvelt simply added letters to the numbers on the dial. To a substantial extent, the story of innovations in telephony is an American story, in part because as late as the s, the U. Separate frames were used for the several parts of the telephone-calling process. His original device was crude and impractical.
Because its operations involved no mechanical motions, electronic switches were faster and easier to maintain. The panel switch was an extremely complex device, with tall panels covered with rows of terminals. About the same time, Gotthief A. Ericsson, which had the resources to prepare it for manufacture.
In Europe, the urban exchanges tended to have fewer telephones and therefore lesser interoffice trunking requirements. Additional improvements by Keith and others at Automatic Electric further improved the switch. Automatic telephone switching was critical in making the telephone the influential mass market technology it became. Crossbar tandems for the first time allowed for automatic alternative routing, when the direct route between exchanges was not available.
By every telephone in Manhattan that connected to a central exchange was a dial telephone connected to a panel switch. Bell Telephone Laboratories, Inc. With the growth of the telephone network, the recruitment and employment of sufficient number of operators had become increasingly problematical. There was similar, but somewhat later development in most of the developed world. Industrial and Corporate Change, vol.
Originally, all telephone calls required the participation of an operator. The units used to establish a call were not only separate from those used for the actual call path, as they had been in the panel, but were common control units. Ericsson was also developing its own variant of the rotary switch, the switch, and in Televerket choose the latter for use in Swedish cities. Both of these featured continuously running motors and clutches that engaged to select electrical contacts.
This meant that there were only small mechanical motions and none of the large sliding movements required in the panel and Strowger switches. Strowger and his backers formed a company, eventually known as the Automatic Electric Company, to develop the patent into a practical switch. However, the crossbar selector proved too expensive at this time to be put into use.
The translator, or the sender as an improved version would become known, introduced the concept of indirect control. Every telephone call required the assistance an operator or, as exchanges began to be connected to other exchanges, multiple operators. Reynolds of Western Electric invented the crossbar selector, in which a small number of magnets operated a large number of relay contacts in a coordinate array.
Thus, it proved easy for Bell Labs to adapt the crossbar switch for use as the first automatic switch in the long distance network. Each panel had an electric motor, to drive its usually sixty selectors by electromagnetically controlled clutches. Under the technical leadership of Alexander E.
The Strowger, or step-by-step switch as it also became known, remained the most widespread switch in use until the s, and it was particularly common in non-urban exchanges. And because electronic switches were essentially special purpose computers, they were more flexible, and could allow for advanced features such as call waiting. The new switch used the crossbar as well as some of their work from earlier in the decade. Crossbar switches were wired to allow for the separation of the two directions of transmission. The second was a new component for the crossbar switch, a so-called pretranslator, which acted after receiving the first three dialed digits.
He sold his invention to the Swedish company L. Thus, the pretranslator could react to the second digit.
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