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Difference between revisions of "Ammeters"
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[[File:Ammeter.gif|thumb|right|Ammeter]] | |||
'''Ammeter''' is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A), hence the name. Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters. Early ammeters were laboratory instruments which relied on the Earth's magnetic field for operation. By the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems. | '''Ammeter''' is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A), hence the name. Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters. Early ammeters were laboratory instruments which relied on the Earth's magnetic field for operation. By the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems. | ||
The relation between electric current, magnetic fields and physical forces was first noted by | The relation between electric current, magnetic fields and physical forces was first noted by | ||
Hans Christian Ørsted who, in 1820, observed a compassneedle was deflected from pointing North when a current flowed in an adjacent wire. The tangent galvanometer was used to measure currents using this effect, where the restoring force returning the pointer to the zero position was provided by the Earth's magnetic field. This made these instruments usable only when aligned with the Earth's field. Sensitivity of the instrument was increased by using additional turns of wire to multiply the effect – the instruments were called multipliers. | Hans Christian Ørsted who, in 1820, observed a compassneedle was deflected from pointing North when a current flowed in an adjacent wire. The tangent galvanometer was used to measure currents using this effect, where the restoring force returning the pointer to the zero position was provided by the Earth's magnetic field. This made these instruments usable only when aligned with the Earth's field. Sensitivity of the instrument was increased by using additional turns of wire to multiply the effect – the instruments were called multipliers. | ||
==Types== | ==Types== | ||
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Digital ammeter designs use an analog to digital converter (ADC) to measure the voltage across the shunt resistor; the digital display is calibrated to read the current through the shunt. Such instruments are generally calibrated to indicate the RMS value for a sine wave only but some designs will indicate true RMS . | Digital ammeter designs use an analog to digital converter (ADC) to measure the voltage across the shunt resistor; the digital display is calibrated to read the current through the shunt. Such instruments are generally calibrated to indicate the RMS value for a sine wave only but some designs will indicate true RMS . | ||
There is also a whole range of devices referred to as integrating ammeters.In these ammeters, the amount of current is summed over time, giving as a result the product of current and time, which is proportional to the energy transferred with that current. These can be used for energy meters or for estimating the charge of battery or capacitor. | There is also a whole range of devices referred to as integrating ammeters.In these ammeters, the amount of current is summed over time, giving as a result the product of current and time, which is proportional to the energy transferred with that current. These can be used for energy meters or for estimating the charge of battery or capacitor. | ||
==Application== | ==Application== | ||