What is an ammeter? What is its structure, function and mechanism?

What is an ammeter

The ammeter is a specialized measuring device used to measure current with a wide range from 100mA to 2000A. This is one of the indispensable devices of electrical engineers.

Not only is it used to measure current intensity, but many types of ammeter are also equipped with modern features such as a multimeter. They can be used to measure voltages, resistors, and frequency measurements. The name of the ammeter is derived from the unit of measurement of the amperage of amperes.

Operation mechanism of the ammeter.

The reciprocal magnetic field produced by the alternating current can induce electromagnetic induction on an inductance near the current.

Functions of the ammeter

With a dedicated design, the ammeter has the main function of measuring the current. Some other types of ammeter also have a variety of functions. Examples include AC voltage measurement, resistance measurement or frequency, temperature measurement as well as inductive testing.

Some common ammeter types

Interfering Ammeter 

When measuring the current that flows in a wire, the intervention ammeter must be connected in series with the wire. Every ammeter consumes a small continuous voltage in the circuit. The ammeter symbol in the circuit is a circle with the letter A in the middle. there may be an additional positive and negative symbol on each side for the DC current.

In many designs, the ammeter is a paint galvanometer. There are many different types of intervention ammeter such as rotating frame, electronic ammeter, ferromagnetic ammeter, thermal ammeter.

Rotary frame Ammeter 

This type of traditional ammeter is often used to measure the intensity of direct current running in an electrical circuit. The main part is a coil. This coil can rotate around an axis, located in the magnetic field of a permanent magnet. The coil is attached to a needle pointing the angle of rotation on an arc. A torsion spring pulls coil and needle to zero position when there is no current. In some instruments, the coil is attached to a piece of iron, subjected to the attraction of the magnets and balanced at zero.

Ampe kế khung quay

Rotary frame Ammeter 

Electronic ammeter

An electronic ammeter is usually an operating mode of electronic multimeters. The active nature of this type of ammeter can be described as an electronic voltmeter that measures the voltage caused by an electric current on a small resistor called shunt. Different scales are adjusted by selecting different shunts. The electric current is derived from the voltage measured by Ohm’s law.

Ampe kế điện tử

Electronic ammeter

Ferromagnetic ammeter

Ferromagnetic ammeter made of two young iron rods located inside a wire tube. One bar is fixed and the other is mounted on the reel, and attached to the needle pointing the angle of rotation on an arc. The electric current through the wire tube produces a magnetic field in the tube. This magnetic field induces ferromagnetic induction on two iron bars, turning them into magnets of the same dimension. Two magnets in the same direction always push each other, regardless of the direction of electric current through the wire tube. Because of this repulsion, the movable magnet rod rotates and the rotation angle corresponds to the current flow through the wire tube.

The ferromagnetic ammeter can measure alternating current since the rotation angle of the needle does not depend on the current direction.

Thermal ammeter

The main part of the thermal ammeter is a long and thin metal rod. It is rolled up like a torsion spring with a fixed mounting head. And the other end is attached to a moving needle on a bow-shaped scale. When the current flows through, the spiral rod heats up to the equilibrium temperature. The heat capacity received from the current is equal to the heat capacity radiating to the environment and thermal expansion, pushing the head freely to rotate. The angle of rotation, shown by the position of the needle head on the scale, corresponds to the current.

Non-Interfering Ammeter 

The Non-Interfering Ammeter has the disadvantage that it needs to be installed as a component in the circuit. This type cannot be used for manufactured circuits that are difficult to change. With these circuits, you need to measure the magnetic field generated by the current. Since then we can determine the intensity of the current.

Ampe kế không can thiệp

Non-Interfering Ammeter

The method of measuring by Non-Interfering Ammeter does not affect the circuit. It also ensures safety for circuits. But sometimes the accuracy is not as high as the intervention method. With this type, you can use a plier ammeter. This device has a Hall effect detector used to measure the electric current intensity.

Hopefully, this article has provided you with useful information about ammeter. Don’t forget to read the next article to update more knowledge.

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