clock face pole-changer telegraph relay

Description:

Telegraph relays amplified electrical signals in a telegraph line. Telegraph messages traveled as a series of electrical pulses through a wire from a transmitter to a receiver. Short pulses made a dot, slightly longer pulses a dash. The pulses faded in strength as they traveled through the wire, to the point where the incoming signal was too weak to directly operate a receiving sounder or register. A relay detected a weak signal and used a battery to strengthen the signal so that the receiver would operate.

This distinctive-looking relay was known as a “clockface pole-changer” and was designed for use on polar duplex circuits powered by wet-cell batteries. Duplex circuits allowed for simultaneous transmission of two messages on the same line. The circuit design was such that operators could not tell which pole of the battery at a distant station might be on line and mismatched polarities interfered with reception. The clockface pole-changer could switch the polarity of the battery at the receiving station to eliminate the problem. A label on the base on this relay cites "Edison patent" although it is unclear which of Edison's six telegraph relay patents (if any) this notation may refer to.

Patentee: Edison, Thomas Alva

Location: Currently not on view

See more items in: Work and Industry: Electricity, Communications, Telegraph Relays & Repeaters

Exhibition:

Exhibition Location:

Credit Line: from Western Union Corporation

Data Source: National Museum of American History

Id Number: EM.294351.016Accession Number: 294351Catalog Number: 294351.016

Object Name: pole changer relaytelegraph relay

Physical Description: wood (overall material)brass (overall material)glass (overall material)metal (overall material)plastic (overall material)Measurements: overall: 5 in x 8 in x 4 1/2 in; 12.7 cm x 20.32 cm x 11.43 cm

Guid: http://n2t.net/ark:/65665/ng49ca746a5-416e-704b-e053-15f76fa0b4fa

Record Id: nmah_700675

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