Zero crossing

Zero crossing

Zero crossing is a commonly used term in electronics, mathematics, and image processing. In mathematical terms, "zero crossing" basically means the changing of sign (e.g. from positive to negative), that is represented with a crossing of the axis (zero-value) in a graph of a particular function.

In electronics

In alternating current, the zero crossing is the instantaneous point at which there is no voltage present. In a sine wave or other simple waveform, this normally occurs twice during each cycle.

The zero crossing is important for systems which send digital data over AC circuits, such as X10 home automation control systems, and Digital Command Control type systems for Lionel and other AC model trains.

Counting zero crossings is also a method used in speech processing to estimate frequencies and formants 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 players, 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 voltage is the key to determining the proper switching time (phase angle) in both leading edge and trailing edge dimmers.

In image processing

In the field of Digital Image Processing, great emphasis is placed on operators which seek out edges within an image. They are called 'Edge Detection' or 'Gradient filters'. A gradient filter 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 [http://www.pages.drexel.edu/%7Eweg22/edge.html]

See also

* Reconstruction from zero crossings
* Zero-crossing rate


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • zero crossing — nulio perėjimas statusas T sritis radioelektronika atitikmenys: angl. zero crossing; zero passage vok. Nulldurchgang, m rus. проход через нуль, m; прохождение через нуль, n pranc. passage par zéro, m …   Radioelektronikos terminų žodynas

  • Zero-crossing rate — The zero crossing rate is the rate of sign changes along a signal, i.e., the rate at which the signal changes from positive to negative or back. This feature has been used heavily in both speech recognition and music information retrieval and is… …   Wikipedia

  • Zero Crossing Rate — Le Zero Crossing Rate (souvent utilisé sous sa forme abrégée ZCR) est le taux de changement de signe d un signal. Le ZCR a beaucoup été utilisé en reconnaissance de la parole et en Recherche d information musicale. Il est défini par: où s est un… …   Wikipédia en Français

  • Zero crossing threshold detector — A zero crossing threshold detector is an electronic circuit that consists of an operational amplifier with an input voltage at its positive input (see circuit diagram). Often used in conjunction with other circuit elements, it usually functions… …   Wikipedia

  • zero passage — nulio perėjimas statusas T sritis radioelektronika atitikmenys: angl. zero crossing; zero passage vok. Nulldurchgang, m rus. проход через нуль, m; прохождение через нуль, n pranc. passage par zéro, m …   Radioelektronikos terminų žodynas

  • Crossing number (graph theory) — A drawing of the Heawood graph with three crossings. This is the minimum number of crossings among all drawings of this graph, so the graph has crossing number cr(G) = 3. In graph theory, the crossing number cr(G) of a graph G is the… …   Wikipedia

  • Crossing number (knot theory) — In the mathematical area of knot theory, the crossing number of a knot is the minimal number of crossings of any diagram of the knot. It is a knot invariant. By way of example, the unknot has crossing number zero, the trefoil knot three and the… …   Wikipedia

  • Reconstruction from zero crossings — The problem of reconstruction from zero crossings can be stated as: given the zero crossings of a continuous signal, is it possible to reconstruct the signal (to within a constant factor)? Worded differently, what are the conditions under which a …   Wikipedia

  • passage par zéro — nulio perėjimas statusas T sritis radioelektronika atitikmenys: angl. zero crossing; zero passage vok. Nulldurchgang, m rus. проход через нуль, m; прохождение через нуль, n pranc. passage par zéro, m …   Radioelektronikos terminų žodynas

  • Evenness of zero — The number 0 is even. There are several ways to determine whether an integer is even or odd, all of which indicate that 0 is an even number: it is a multiple of 2, it is evenly divisible by 2, it is surrounded on both sides by odd integers, and… …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”