DC bias

When describing a periodic function in the time domain, the DC bias, DC component, DC offset, or DC coefficient is the mean value of the waveform. If the mean amplitude is zero, there is no DC offset. In contrast, various other frequencies are analogous to superimposed AC voltages or currents, hence called AC components or AC coefficients.

The term originated in electronics, where it refers to a direct current voltage, but the concept has been extended to any representation of a waveform. The term's use is extended to two-dimensional transformations like the discrete cosine transform used in JPEG.

A waveform without a DC component is known as a DC-balanced or DC-free waveform. DC-balanced waveforms are useful in communications systems to avoid voltage imbalance problems between connected systems or components.

DC offset is usually undesirable when it causes saturation or change in the operating point of an amplifier. An electrical DC bias will not pass through a transformer; thus a simple isolation transformer can be used to block or remove it, leaving only the AC component on the other side. In signal processing terms, DC offset can be reduced in real-time by a high-pass filter. When one already has the entire waveform, subtracting the mean amplitude from each sample will remove the offset. Often, very low frequencies are called "slowly changing DC" or "baseline wander".

Offset

Offset may refer to:

Science and engineering

Wheel

A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the main components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be moved easily facilitating movement or transportation while supporting a load, or performing labor in machines. Wheels are also used for other purposes, such as a ship's wheel, steering wheel, potter's wheel and flywheel.

Common examples are found in transport applications. A wheel greatly reduces friction by facilitating motion by rolling together with the use of axles. In order for wheels to rotate, a moment needs to be applied to the wheel about its axis, either by way of gravity, or by the application of another external force or torque.

Etymology

The English word wheel comes from the Old English word hweol, hweogol, from Proto-Germanic *hwehwlan, *hwegwlan, from Proto-Indo-European *k^wek^wlo-, an extended form of the root *k^wel- "to revolve, move around". Cognates within Indo-European include Icelandic hjól "wheel, tyre", Greek κύκλος kúklos, and Sanskrit chakra, the latter both meaning "circle" or "wheel".

Parallel curve

A parallel of a curve is the envelope of a family of congruent circles centered on the curve. It generalises the concept of parallel lines. It can also be defined as a curve whose points are at a fixed normal distance from a given curve. These two definitions are not entirely equivalent as the latter assumes smoothness, whereas the former does not.

A parallel curve is also called an offset curve and this is the preferred term in CAGD. (In other geometric contexts, the term offset can also refer also to translation.) Offset curves are important for example in numerically controlled machining, where they describe for example the shape of the cut made by a round cutting piece of a two-axis machine. The shape of the cut is offset from the trajectory of the cutter by a constant distance in the direction normal to the cutter trajectory at every point.

In the area of 2D computer graphics known as vector graphics, the (approximate) computation of parallel curves is involved in one of the fundamental drawing operations, called stroking, which is typically applied to polylines or polybeziers (themselves called paths) in that field.