What is an ammeter?

An ammeter is a device used to measure direct or alternating electrical current in the ampere unit, which is the unit of measuring current intensity. Current is the flow of electrons through a circuit, and the ammeter is known as a measure of current.

The ammeter can measure a wide range of current values, because at high values ​​only a small part of the current is directed through the meter mechanism, and the shunt in parallel with the meter carries the largest part. The ammeter is a device modified from the galvanometer that is used to measure the intensity of large electrical currents, and it is completely different. About the voltmeter.

The ammeter does not have internal resistance, however in practice it has a small internal resistance, and the field of measurement of the ammeter depends on the amount of resistance.

Types of ammeter device

The classification of ammeter devices depends on their design and the type of flow that passes through the device. Below are the types of ammeter in relation to the design

• An ammeter with a permanent moving magnet
• Moving magnet ammeter
• Electrodynamic ammeter
• Ammeter is a rectifier

It has types depending on the type of current used

• An ammeter measures direct current (DC).
• An ammeter measures alternating current (AC).

PMMC permanent magnet ammeter

In this device, the conductor is placed between the two poles of a permanent magnet, and when the current passes through the coil, it begins to deviate. The deflection of the coil depends on the size of the current flowing through it, and the PMMC meter is used to determine the value of the direct current, because the deflection here is proportional to the current, and therefore if the direction of the current, the deflection of the pointer will also be inverted so that it is only turned on to measure DC current.

This type of device has the great advantage of having a linear scale, low power consumption, high accuracy, the main disadvantage is to measure DC current quantity only, high cost etc.

MI moving magnet ammeter

The MI ammeter is used to determine the value of alternating current and direct current. In this model of ammeter, the coil moves independently between the poles of a permanent magnet. When the current passes through the coil, it begins to deviate at a specific angle, and the deflection of the coil is proportional to the current that flows through the coil.

Electrodynamic ammeter

It is exploited to find out the value of DC current and AC current the same, the accuracy of the device is high compared to PMMC and MI instrument, the calibration of the device is the same for both AC and DC current, i.e. if the device is calibrated to measure DC current then without recalibration it can be used to measure AC current.

Ammeter rectifying the current

It is used to know the value of alternating current, and devices that use a rectifying ammeter change the path of the current and pass it to the PMMC device. These devices are used to measure current in the communications circuit, and one of its advantages is that it can also be used in high frequencies, and is a unified measure for most ranges   , but One of the most important disadvantages is that an error occurs due to low temperature during sensitivity measurement in AC operation.

Connecting the ammeter to the electrical circuit

The ammeter is connected in series with the circuit so that the electrons of the measured current pass completely through the ammeter. The power loss in the ammeter occurs due to the ammeter and their internal resistance. The ammeter circuit is characterized by low resistance so that a small voltage drop occurs in the circuit. For this reason, the resistance of the ammeter is kept low.

Effect of temperature on ammeter

The ammeter is a sensitive device that is easily affected by the ambient temperature, the difference in temperature causes reading error, this can be reduced through the immersion resistance, where the resistance having zero temperature coefficient is known as the immersion resistance, which is connected in series with the ammeter, The immersion resistance reduces the effect of temperature on the meter.

The ammeter contains a fuse that carries properties that protect the ammeter from heavy current. If a large current flows through the ammeter, the fuse will break, and the ammeter will be unable to measure the current so that the new current does not replace the fuse.

The working principle of the ammeter

The main principle of a device that measures electric current is that it must have a very low resistance, and also an inductive reactance, and we cannot connect an ammeter in parallel, because it has a very low resistance, so it must have a very low amount of voltage across it, and it must To be connected in a series connection, because the current is the same in a series circuit.

Also due to the very low impedance, the power loss will be low, and if it is connected in parallel the circuit path becomes almost short, and all the current will flow through the ammeter, and as a result of high current the device may burn, for this reason it must be connected in series, and these are from the laws of electric current intensity.

To obtain an ideal ammeter and know how the intensity of electric current is calculated, the device must have zero impedance so that there is no voltage drop across it, so the power loss in the device is zero, but the ideal cannot be achieved in practice.

The difference between an ammeter and a galvanometer

• Galvanometer and ammeter are both measuring instruments, and the electric ammeter is the applied form of the galvanometer, which shows the exact value of the current passing through it in millimeters or amperes.
• The most important difference between a galvanometer and an ammeter is that a galvanometer is a mechanical device used to determine the amount and direction of a current, while an ammeter is an electrical device used to measure the magnitude of a current. A galvanometer shows the direction of current flow in a circuit, while an ammeter shows the amount of current. The current flowing through it
• A galvanometer uses a moving coil that can be rotated between permanent magnets, and when current flows through the coil, it deflects it, and the deflection of the coil is directly proportional to the current flowing through it
• The galvanometer is converted into an ammeter by connecting the resistance in parallel with the circuit, and if the resistance is connected in series with the galvanometer, it is exploited as a voltmeter
• Ammeter is also known as ampere meter, ampere is the unit of measurement for electric current in the international system, so ampere meter is a type of meter that measures the magnitude of current passing through it, which is connected in series with the circuit to determine the exact value of the circuit current
• The magnetic field is required to operate the galvanometer, while it is not required for the ammeter, and the accuracy of the galvanometer is less compared to the ammeter.
• The galvanometer is only used to measure direct current, while the ammeter is used to measure both direct and alternating current, and the sensitivity of the galvanometer is greater compared to the ammeter.
• The galvanometer is commonly used in bridge and voltage standard to find out the zero current, while the ammeter is directly connected in series with the circuit whose magnitude it will complete the measurement.