This is achieved by using a sensitive galvanometer in series with a high resistance, and then the entire instrument is connected in parallel with the circuit examined.

One of the design objectives of the instrument is to disturb the circuit as little as possible and so the instrument should draw a minimum of current to operate. The deflection of the coil is thus proportional to the current, which in turn is proportional to the applied voltage, which is indicated by a pointer on a scale. The coil rotates, compressing a spring that opposes the rotation. The torque is proportional to the current through the coil. When an electric current is applied, the interaction of the magnetic field of the coil and of the stationary magnet creates a torque, tending to make the coil rotate. The galvanometer has a coil of fine wire suspended in a strong magnetic field.

N and S are the north and south poles of the magnet.Ī moving coil galvanometer can be used as a voltmeter by inserting a resistor in series with the instrument.

The restoring spring is shown in green.

The red wire carries the current to be measured.

In circuit diagrams, a voltmeter is represented by the letter V in a circle, with two emerging lines representing the two points of measurement. Precision voltage references are available based on electronic circuits. In laboratories, the Weston cell is used as a standard voltage for precision work. Part of the problem of making an accurate voltmeter is that of calibration to check its accuracy. Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million. Digital meters can be made with high accuracy, typically better than 1%. General-purpose analog voltmeters may have an accuracy of a few percent of full scale and are used with voltages from a fraction of a volt to several thousand volts. Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated for example, pressure, temperature, flow or level in a chemical process plant. Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter are standard test instruments used in electrical and electronics work. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus. by battery), and others powered by the measured voltage source itself.

Voltmeters are made in a wide range of styles, some separately powered (e.g. Digital voltmeters give a numerical display of voltage by use of an analog-to-digital converter.

Meters using amplifiers can measure tiny voltages of microvolts or less. It usually has a high resistance so that it takes negligible current from the circuit.Īnalog voltmeters move a pointer across a scale in proportion to the voltage measured and can be built from a galvanometer and series resistor. ( Learn how and when to remove this template message)Ī voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit.

JSTOR ( February 2024) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. An editor has performed a search and found that sufficient sources exist to establish the subject's notability.

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