Thomson Recording Wattmeter prepayment (1899-1903) Up
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With the success of prepayment gas meters, GE decided to apply this concept to electric metering and introduced a special version of the TRW in 1899. This system consisted of two parts, a specially modified TRW (these have a register marked off to indicate the credit remaining per coin in addition to the normal watthour usage) and a prepayment device. At first, the Form 1 device (see center picture) was used, but this was replaced in 1901 by the Form 2 device (right). Both versions were built to take dimes and wound up a mainspring each time a dime was inserted. The dime interlocked the handle with the the mainspring gear and fell into the collection box at the bottom which had its own seal. The coin box could easily be exchanged with an empty one by the meter reader without emptying it. The meter had a contact device that completed a circuit at a preset interval and briefly energized the coil within the prepayment device, unwinding the spring notch by notch until a stop on the gear made contact with the switch, opening the circuit. In 1903, the TRW prepayment was superseded by two lines of prepayment meters: The IP series for use on AC circuits and CP series for use on DC circuits.
 
Thomson Recording Wattmeter
David Dahle collection
Form 1 prepayment
GE prepayment metering pamphlet
Form 2 prepayment
GE prepayment metering pamphlet