Bunnell "double-balanced" relay
date: label: date made
content: ca 1900
name: label: maker
content: Bunnell Telegraphic and Electrical Co.
notes: label: Description
content: 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.
label: Description
content: This is a special type of relay made by Bunnell called a "double-balanced" relay and was designed for use in a burglar alarm circuit. Each coil is wound to 150 ohms and are in electrical series on the telegraph line. One coil activates the alarm bell if the current drops, the other coil activates the alarm if the current rises, making it difficult to quietly tamper with the circuit.
label: Location
content: Currently not on view
setName: label: See more items in
content: Work and Industry: Electricity
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content: Communications
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content: Telegraph Relays & Repeaters
creditLine: label: Credit Line
content: from Western Union Corporation
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: EM.332503
label: accession number
content: 294351
label: catalog number
content: 332503
label: collector/donor number
content: 94-01
objectType: label: Object Name
content: relay
label: Object Name
content: telegraph relay
label: Other Terms
content: telegraph relay; Telegraphy
physicalDescription: label: Physical Description
content: wood (overall material)
label: Physical Description
content: brass (overall material)
label: Physical Description
content: steel (overall material)
label: Physical Description
content: plastic (overall material)
label: Measurements
content: overall: 4 1/8 in x 7 5/8 in x 4 1/4 in; 10.4775 cm x 19.3675 cm x 10.795 cm