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An ampere-hour or amp-hour (symbol: A⋅h or A h; often simplified as Ah) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3,600 coulombs.
Some meters measure currents as low as milliamps or even microamps. All meters have a burden voltage (caused by the combination of the shunt used and the meter's circuit design), and some (even expensive ones) have sufficiently high burden voltages that low current readings are seriously impaired. Meter specifications should include the burden ...
Factor () Value Item 10 −19: 160 zA Current flow of one electron per second : 10 −12: 1-15 pA Range of currents associated with single ion channels [calcium (1 pA), sodium (10-14 pA), potassium (6 pA)] as measured by patch-clamp studies of biological membranes
Ammeter from the old New York Penn Station terminal service plant in New York City. The relation between electric current, magnetic fields and physical forces was first noted by Hans Christian Ørsted in 1820, who observed a compass needle was deflected from pointing North when a current flowed in an adjacent wire.
The ampere is named for French physicist and mathematician André-Marie Ampère (1775–1836), who studied electromagnetism and laid the foundation of electrodynamics.In recognition of Ampère's contributions to the creation of modern electrical science, an international convention, signed at the 1881 International Exposition of Electricity, established the ampere as a standard unit of ...
This is used to calculate the numerical value of the current. The main weakness of the ampere balance is that the calculation of the current involves the dimensions of the coils. So the accuracy of the current measurement is limited by the accuracy with which the coils can be measured, and their mechanical rigidity.
Depending on the source of current for the loop, devices may be classified as active (supplying or "sourcing" power) or passive (relying on or "sinking" loop power). For example, a chart recorder may provide loop power to a pressure transmitter.
This page was last edited on 19 March 2005, at 09:05 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may ...