AC Current
AC, or Alternating Current, is a type of electric current that periodically reverses direction, oscillating between positive and negative values. In an AC circuit, the electric charge flows first in one direction and then in the opposite direction, constantly reversing its direction at a certain frequency.
The most common example of AC current is the electricity that is delivered to our homes and businesses by the power grid. AC current is preferred for long-distance power transmission because it can be easily stepped up to high voltages for transmission over long distances with less power loss, and then stepped down to lower voltages for use in homes and businesses.
The frequency of AC current is typically measured in Hertz (Hz), which refers to the number of times the current oscillates back and forth in one second. In the United States, the standard frequency of AC power is 60 Hz, while in some other countries it is 50 Hz.
In addition to power transmission, AC current is also used in a wide range of electrical and electronic devices, from small appliances to industrial machinery. AC current can be converted to DC (Direct Current) using devices like rectifiers, which are commonly used in electronic devices like computers and mobile phones.
AC Current – Measurement
Ammeters are used to measure the electric current flowing through a circuit. There are three basic types of ammeters for measuring AC (Alternating Current) current:
- Moving Coil Ammeters: Moving coil ammeters use a coil that moves in a magnetic field to measure the current flowing through a circuit. When current flows through the coil, it creates a magnetic field that interacts with the magnetic field of a permanent magnet, causing the coil to move. The movement of the coil is proportional to the current flowing through the circuit, and this movement is converted into a current reading. When an AC with a very low frequency is passed through a PMMC, the pointer tends to follow the instantaneous level of the AC. Therefore, a PMMC instrument connected directly to measure 50Hz AC indicates zero average value. It is important to note that although a PMMC instrument connected to an ac supply may indicating zero, there can actually be very large rms current flowing in its coils. To convert alternating current (AC) to unidirectional current flow, which produces positive deflection when passed through a PMMC, the diode rectifier is used.
- Digital Ammeters: Digital AC ammeters measure AC current passing through a circuit by converting it into a proportional digital signal. The AC current is passed through a current transformer to step down the current to a safe level for measurement. The output of the current transformer is then rectified to a DC voltage using a rectifier circuit. The DC voltage is then converted into a digital signal using an Analog to Digital Converter (ADC) circuit. The microcontroller receives the digital signal and processes it to display the current value on the screen. The final step is to display the current value on an LED or LCD display.
- Clamp-On Ammeters: Clamp-on ammeters are designed to measure the current flowing through a wire without having to physically disconnect the wire. The ammeter has a clamp that can be opened and placed around the wire to measure the current flowing through it. Clamp-on ammeters are often used in industrial settings where large wires and cables need to be measured.
When selecting an ammeter for measuring AC current, it is important to choose one that is rated for the maximum current that will be measured. Ammeters that are rated for higher currents will typically have a lower resistance, which can cause a voltage drop in the circuit being measured. Therefore, it is important to select an ammeter that has a low resistance compared to the circuit being measured. It is also important to select an ammeter with a frequency range that matches the frequency of the AC current being measured.
Rectification and AC Ammeters
Rectification is the process of converting an AC (alternating current) signal into a DC (direct current) signal. AC current alternates in polarity, meaning it flows in one direction and then the other, constantly changing direction. This can be visualized as a wave that oscillates both above and below a zero point, which is also known as the “zero crossing.”
In order to convert an AC signal to DC, the negative half of the AC waveform must be eliminated or “rectified.” This is typically done by using a diode, which is a one-way valve for current flow. A diode allows current to flow in one direction, but blocks it from flowing in the other direction. By placing a diode in series with the AC signal, the negative half of the waveform is blocked, effectively turning the AC signal into a unidirectional or DC signal.
There are two types of rectifiers: half-wave rectifiers and full-wave rectifiers. A half-wave rectifier uses one diode to rectify the AC signal, while a full-wave rectifier uses four diodes arranged in a specific pattern to rectify both the positive and negative halves of the AC signal.
Rectification is an important process in electronics because many electronic devices require DC power to operate, while AC power is commonly available in the power grid. Rectification allows AC power to be converted into DC power for use in electronic circuits and devices.
