About This Item
all original and exceptionally rare oversized astatic switchboard type thomson electromechanical watthour meter designed and fabricated by the general electric company, schenectady, ny. the “cs” type direct current, three-wire electricity meter was first introduced in 1907. the thomson watthour meter (the so-called ” recording wattmeter”) is the earliest example of an american direct-current motor meter, and most other direct-current watthour meters differ from it only in details of design and construction. this meter contains a double set of current coils and the moving element is 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 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 wound with fine wire, is connected through a series resistance across the line. on the shaft of the motor is a disk of copper or aluminum which rotates between the poles of several permanent magnets. the upper end of the armature shaft has a worm which engages with the first gear wheel of the register. the intricate instruments are fully enclosed in a reinforced cast brass frame containing clear glass panels. the top-mounted kilowatt hour readout is comprised of four diminutive dials meters mounted against a white porcelain enameled copper backplate. the meter remains in exceptional original condition with intact mounting studs and threaded terminal plugs found on the backside. weighs nearly 95 pounds. measures 11 1/2 x 9 x 20 inches. salvaged from an old movie house located in st. louis, mo.