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  ABDNP200280a01.JPG - Warden, Muirhead & Clark Telegraph Relay The 19th century telegraph ushered in many of today's communication techniques.  Among these are digital message coding, digital transmission technology, machines for automatic message sending and printing, multiplexing several machines on a single line, fax image transmission and a wired infrastructure around the world.  Yet another development within telegraphy was the separation of the transmitted message signal from the operation of receiving devices.  It takes significant power to ring an electric bell or operate an automatic printer.  This power is best provided locally, not though the message line. The Siemens polarised relay was the key to separating the message signal from the local action.  In it a soft iron lever sits balanced between the attractions of two similar poles provided by a permanent magnet.  The signal line current passes through coils that reduce the magnetism on one side and increase it on the other, thereby unbalancing the lever which moves to the side and makes a local electrical contact.  The bell, or whatever, is rung using a local circuit that runs through the local contact. ABDNP:200280a  
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12 | Warden, Muirhead & Clark Telegraph Relay

The 19th century telegraph ushered in many of today's communication techniques. Among these are digital message coding, digital transmission technology, machines for automatic message sending and printing, multiplexing several machines on a single line, fax image transmission and a wired infrastructure around the world. Yet another development within telegraphy was the separation of the transmitted message signal from the operation of receiving devices. It takes significant power to ring an electric bell or operate an automatic printer. This power is best provided locally, not though the message line.

The Siemens polarised relay was the key to separating the message signal from the local action. In it a soft iron lever sits balanced between the attractions of two similar poles provided by a permanent magnet. The signal line current passes through coils that reduce the magnetism on one side and increase it on the other, thereby unbalancing the lever which moves to the side and makes a local electrical contact. The bell, or whatever, is rung using a local circuit that runs through the local contact.

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