Aron's first double pendulum clock electricity meter
The world’s first accurate and readable electricity meter was patented as the “Pendelzähler” by Dr Aron in Germany in 1883. Surviving examples of this first model where the clocks had to be manually wound each month would appear to be vanishingly rare. The later examples were self-winding using electricity. The meter measures DC electricity consumption in watt-hours and is housed in a glazed oak case 28” (71 cm) x 14.5” (37 cm) x 6.75” (17 cm).
Operation: two separate key wound month-going clocks, each controlled by its own pendulum are mounted on the same bed plate. The last wheels of the train of each clock are so geared together that if the clocks are going at the same rate the counting dials are not affected. If however, one clock gains on the other, the dials register the total gain. The pendulum on the left is a normal pendulum with the usual adjustments. The alteration of the swing of the pendulum with a magnetic bob on the right however depends on the magnetic effect of the current in the solenoid over which it swings. As the solenoid has no iron core its magnetic effect is strictly proportional to the current in the wire, hence the right hand clock errs at a rate at a rate proportional to the watts and therefore the total error in a given time is proportional to the total of the energy consumed.
Dr Aron sold his first meters (100 units) to the Berlin electricity suppliers in 1885. In 1888 Aron meters were sold (and later manufactured) in the UK by the General Electric Company. This meter was supplied to one of the London electricity generating stations in the mid 1890s. The paper attached to the back of the case records that the meter was repaired or serviced in April 1903 and July 1907.
The quality of the clockwork is quite exceptionally fine, both clocks are in working order. All serial numbers match throughout.
See also Professor Elihu Thomson's Recording Wattmeter on this web site for further information on the world's first electricity meters. Transport at cost.
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