early 20th century new york city transit subway substation cast iron thomson astatic ammeter with a largely intact copper-plated finish on the front case

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SKU
UR-20890-14
general electric, schenectady, n.y., u.s.a.

 

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unusually shaped original early 20th century heavy cast iron new york city subway substation switchboard type thomson astatic ammeter designed and fabricated by or for the general electric, schenectady, n.y., u.s.a. the copper-plated cast iron ammeter was originally affixed to a massive control or switch panel housed within a new york city subway substation (see ammeters "in situ" from a period photograph). the meter likely contains (it has not been opened) a double set of current coils with the moving element composed of two armatures astatically arranged on a single shaft so that any uniform magnetic field tending to weaken the torque produced by one armature will strengthen the torque of the other by a like amount. the magnets are also liklely astatically arranged and enclosed in a laminated shield of soft steel punchings to protect them from external magnetic fields and the strong fields caused by short circuits through the meter. the line current passes through the fixed field windings, and the armature, which is usually is wound with fine wire, is connected through a series resistance across the line. the recessed region on the front face of the case contains the darkened scale, but the indicator is no longer present. there was likely a panel of clear glass that protected both the integrity of the scale and indicator arrow. the brushed metal finish has been sealed with a clear coat lacquer. very unique and distinctive piece of new york city subway history. measures 9 x 9 1/2 x 4 1/2 inches.

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