By :- ARUN KUMAR TGT-WE KV NO-1, HBK DEHRADUN PROJECT ON Ammeter , voltmeter and Multi Meter By :- ARUN KUMAR TGT-WE KV NO-1, HBK DEHRADUN

Electric Meters Electric meters are instruments used to measure electrical values. Two common meters are the ammeter and the voltmeter, both of which are variations of the galvanometer. A small magnet inside a galvanometer sets up a magnetic field, generating a measurable force when current flows through a nearby coil. The meter mechanisms are shown here schematically

Ammeter The ammeter diverts electricity through a coil via a shunt (illustrated beneath the device), measuring the amount of current flowing through the circuit in amperes. It is connected in series, or directly in the line of the circuit.

voltmeter The voltmeter is connected in parallel, so that the light bulb falls between its two connections into the circuit. It is designed to measure potential differences. the voltage can be measured if the galvanometer is calibrated appropriately. By using the proper values of series resistors, one galvanometer can be used to measure a large range of voltages.

MEASUREMENTS OF CURRENT A Galvanometers Galvanometers are the main instruments used to detect and measure current. They depend on the fact that force is generated by an electric current flowing in a magnetic field. The mechanism of the galvanometer is so arranged that a small permanent magnet or electromagnet sets up a magnetic field that generates a force when current flows in a wire coil adjacent to the magnet. Either the magnet or the adjacent coil may be movable. The force deflects the movable member by an amount proportional to the strength of the current. The movable member may have a pointer or some other device to enable the amount of deflection to be read on a calibrated scale.

A Galvanometers In the D'Arsonval reflecting galvanometer, a small mirror attached to a movable coil reflects a beam of light on a scale of about 1 m (3 ft) away from the instrument. This arrangement involves less inertia and friction than does a pointer, and consequently, greater accuracy is achieved. The instrument is named after the French biologist and physicist Jacques d'Arsonval. The addition of a scale and proper calibration converts a galvanometer into an ammeter, the instrument used for measuring electric current in amperes. D'Arsonval was also responsible for inventing a direct-current (DC) ammeter

Difference between Ammeter and Voltmeter   Ammeter Voltmeter Connection It is to be connected in series mode It is to be connected in parallel mode Resistance It has comparatively low resistance It has high resistance Uses It is used to find the amount of current flowing in the circuit It is used to find the potential difference in the circuit Circuit Circuit must be disconnected in order to attach the ammeter Circuit does not need to be disconnected Accuracy Considered as less accurate Considered as more accurate compared to ammeter Design Ammeter were based on moving coil galvanometers and were created by inserting a resistor in parallel with the instrument. voltmeters were based on moving coil galvanometers and were created by inserting a resistor in series with the instrument. It uses a small coil of fine wire suspended in a strong magnetic field.

Multimeter Multimeters can also be utilized in place of both ammeters and voltmeters. A multimeter is an instrument that can be used to measure both, currents as well as voltages. It can also perform as ohmmeters, a device used to measure resistance. Multimeters are available in analog or digital format.

Ammeter Design

Multimeter Design

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