Shallenberger Ampere-hour Meter (1888 to 1897) Up
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This was the first successful AC ampere-hour meter developed by Oliver B. Shallenberger, Westinghouse's chief electrician. In 1888, he and an assistant were working on a new AC arc lamp one day and a spring fell out, landing on a ledge inside the lamp. The assistant went to replace the spring, but Mr. Shallenberger noticed the spring was rotating slowly due to fields within the lamp and told the assistant to wait until they figured out why the spring was rotating. After some investigation, Mr. Shallenberger declared that he could come up with a meter based on the principle of that rotating spring, and after only three weeks of rapid-fire experimenting, he had a working design ready for market. This meter paved the way for acceptance of the more efficient AC distribution system over DC. This meter had one disadvantage - it measured all the current flowing through the circuit regardless of the load which made it unsuitable for use with motors, because there was no voltage element to take power factor into account. The motor inside this meter was not much different from the shaded-pole AC motors commonly used today. In order to keep the meter's speed proportional to the amperes, this meter used a fan assembly for the brake. Unlike other meters of its day, this meter fastened to the wall by means of the two wooden straps on the back.
 
Shallenberger amp-hour meter
Charles Crider collection
Meter internals
Charles Crider collection