Zero crossing

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Zero crossing

Zero-crossing is a commonly used term in electronics, mathematics, and image processing. In mathematical terms, a "zero-crossing" is a point where the sign of a function changes (e.g. from positive to negative), represented by a crossing of the axis (zero value) in the graph of the function.

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Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
, the zero-crossing is the instantaneous point at which there is no voltage

Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
present.

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Encyclopedia

In electronics

In alternating current

Alternating current

Voltage

Sine wave

The sine wave or sinusoid is a function that occurs often in mathematics, physics, signal processing, hearing , electrical engineering, and many other fields....
or other simple waveform

Waveform

Waveform means the shape and form of a signal such as a wave moving in a solid, liquid or gaseous medium.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form....
, this normally occurs twice during each cycle

Interval (time)

With regards to time, an interval or period is the duration between two Spacetime#Basic conceptss or occurrences of similar events. It is related to the mathematical concept of interval in that the interval contains all of the Point s of time between the two events....
.

The zero-crossing is important for systems which send digital

Digital

A digital system uses discrete values, usually but not always symbolized numerically to represent information for input, processing, transmission, storage, etc....
data

DATA

Debt, AIDS, Trade in Africa is a multinational Non-governmental organization founded in January 2002 in London by U2's Bono along with Robert Sargent Shriver III and activists from the Jubilee 2000 Drop the Debt campaign....
over AC circuits

Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches....
, such as X10

X10 (industry standard)

X10 is an international and open industry standard for communication among electronic devices used for home automation, also known as domotics....
home automation

Home automation

Home automation is a field within building automation, specializing in the specific automation requirements of private homes and in the application of automation techniques for the comfort and security of its residents....
control system

Control system

A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.There are two common classes of control systems, with many variations and combinations: logic gate, and feedback or linear controls....
s, and Digital Command Control

Digital Command Control

Digital Command Control systems are used to operate locomotive on a model railroad . Equipped with DCC, locomotives on the same electrical section of track can be independently controlled....
type systems for Lionel

Lionel

Lionel is a male given name, and it may refer to:*Lionel Corp., an American manufacturer and retailer of toy trains and model railroads*Lionel, LLC, an American designer and importer of toy trains and model railroads, owns the trademarks and most of the product rights associated with Lionel Corp., but is not directly related...
and other AC model trains.

Counting zero-crossings is also a method used in speech-processing to estimate frequencies and formant

Formant

A formant is a peak in the frequency spectrum of a sound caused by Acoustics resonance. In phonetics, the word refers to sounds produced by the vocal tract....
s of speech.

In a system where an amplifier with digitally-controlled gain is applied to an input signal, signal artifacts will occur when the gain of the amplifier abruptly switches between its discrete gain settings while outputting a non-zero current. At audio frequencies, such as in modern consumer electronics like digital audio player

Digital audio player

A digital audio player, more commonly referred to as an MP3 player, is a consumer electronics device that stores, organizes and plays audio file formats....
s, these effects are clearly audible, resulting in a 'zipping' sound when rapidly ramping the gain, or a soft 'click' when a single gain change is made. Artifacts are disconcerting and clearly not desirable. If changes are made at a zero-crossing of the signal, the input is zero, so no matter how the amplifier gain setting changes, the output will also remain at zero.

The zero-crossing of the mains

Mains

Mains may mean or refer to, or be a subject of:* Mains electricity * Electricity transmission* Public utility, about "mains services", including electricity, natural gas, water, and sewage disposal...
voltage

Voltage

Phase angle

In the context of vectors and Phasor , the term phase angle refers to the angular component of the polar coordinate representation. The notation for a vector with magnitude A and phase angle ?, is called angle notation....
) in both leading edge and trailing edge dimmers.

In image processing

In the field of Digital

Digital

A digital system uses discrete values, usually but not always symbolized numerically to represent information for input, processing, transmission, storage, etc....
Image Processing

Image processing

In electrical engineering and computer science, image processing is any form of signal processing for which the input is an , such as photographs or video frame; the output of image processing can be either an image or a set of characteristics or parameters related to the image....
, great emphasis is placed on operators which seek out edges within an image. They are called 'Edge Detection' or 'Gradient filters'. A gradient filter

Edge detection

Edge detection is a terminology in and computer vision, particularly in the areas of feature detection and feature extraction, to refer to algorithms which aim at identifying points in a digital image at which the luminous intensity changes sharply or more formally has discontinuities....
is a filter which seeks out areas of rapid change in pixel value. These points usually mark an edge or a boundary. A Laplace filter is a filter which fits in this family, though it sets about the task in a different way. It seeks out points in the signal stream where the digital signal of an image passes through a pre-set '0' value, and marks this out as a potential edge point. Because the signal has crossed through the point of zero, it is called a zero-crossing. For a more complete explanation, try visiting . An other example can be find , including the source in Java.

Zero crossing

In electronics

In image processing

See also