Line (electrical engineering)

Line (electrical engineering)

In electrical engineering, a line is, more generally, any circuit (or loop) of an electrical system. This electric circuit loop (or electrical network), consists of electrical elements (or components) connected directly by conductor terminals to other devices in series.

=Overview=Consumer electronic devices concerned with audio (for example Sound cards) often have a connector labeled "line in" and/or "line out". Line out provides an audio signal and line in receives one. The connection is typically unbalanced using a TRS connector of 6.35mm (1/4"), 3.5mm (1/8" miniature) or 2.5mm (3/32" subminiature).

For example, while recording from the line output of a stereo FM receiver, you can turn up the speaker volume for your favorite song, then turn the volume back down after it ends while you record. When you play back the recording, having only changed the speaker volume, all the songs will be at the same loudness; you will not hear the volume increase where you turned up your favorite song (assuming that the radio station was broadcasting all the songs at the same volume level). In contrast, if you recorded by connecting to the speaker or headphone connector, the recording's volume would follow the volume knob's setting.

=Line out=The signal out of line out remains at a constant level, regardless of the current setting of the volume control. You can connect recording equipment to line out and record the signal, without having to listen to it through the device's speaker, and without the loudness of the recording changing if you change the volume control setting of the device while you are recording.

The impedance is around 100 ohms, the voltage can reach 2 volts peak-to-peak with levels referenced to -10 dBV (300 mV) at 10k ohms, and frequency response of most modern equipment is advertised as 20Hz-20kHz (although other factors influence frequency response). This impedance level is much higher than the usual 4 or 8 ohms of a speaker, such that a speaker connected to line out essentially short circuits the op-amp. Even if the impedances would match, yielding the theoretical maximum power transfer of 50%, the power supplied through line out is not enough to drive a speaker.

=Line in=Line in expects the kind of voltage level and impedance that line out provides. You can typically connect the line out connector of one device with the line in of another. However, doing this with a straight cable directly connected to both devices and having both devices on AC power, you may run into a ground loop; although some devices provide isolation by using an opto-isolator, which does not create a physical connection of the devices.

A line input has a high impedance of around 10,000 ohms, as is often labeled as "Hi-Z" input (Z being the designator for impedance).

=Impedances=The desired effect is to have the impedances far from matched (10,000 ohm to 100 ohm) so that very little power is transferred and the line in circuit does not load down the output of the other device. When a line out signal, with its impedance of around 100 ohms, is connected to the high impedance line in of 10k ohms, most of the voltage appears across the input resistance and almost none of the voltage is dropped across the output.

=Information transfer=These are voltage signals (as opposed to current signals) and it is the signal information (voltage) that is desired, not power to drive a transducer, such as a speaker or antenna. The actual information that is exchanged between the devices is the variance in voltage; it is this alternating voltage signal that conveys the information, making the current irrelevant.

Wikimedia Foundation. 2010.

См. также в других словарях:

  • Signal (electrical engineering) — In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time varying or spatial varying quantity. In the physical world, any quantity measurable through time or over space can be taken as… …   Wikipedia

  • Bias (electrical engineering) — In electrical engineering, the term bias has the following meanings: # A systematic deviation of a value from a reference value. # The amount by which the average of a set of values departs from a reference value. # Electrical, mechanical,… …   Wikipedia

  • List of electrical engineering topics (alphabetical) — This page aims to list, alphabetically, all articles related to the specific discipline of electrical and electronics engineering. For a thematic list, please see List of electrical engineering topics. For the broad field of engineering, see List …   Wikipedia

  • History of electrical engineering — This article details the history of electrical engineering. Topics also included are the general developments and notable individuals within the electrical engineering profession. Ancient developmentsThales of Miletus, writing at around 600 BC,… …   Wikipedia

  • List of electrical engineering topics — This is a listing of electrical engineering and electronic engineering topics and related terms. Contents 1 Electromagnetism 2 Physical laws 3 Control engineering 4 Electronics …   Wikipedia

  • Daisy chain (electrical engineering) — In electrical and electronic engineering a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring.[1] Other than a full, single loop, systems which contain internal loops cannot be called daisy chains …   Wikipedia

  • Line — or lines may refer to: * Line (geometry), an infinitely extending one dimensional figure that has no curvature * a length of rope, cable or chain when put to use (such as a clothesline, anchor line) * a line or queue of people waiting in a queue… …   Wikipedia

  • Engineering education — is the activity of teaching knowledge and principles related to the professional practice of engineering. It includes the initial education for becoming an engineer and any advanced education and specialization that follow. Engineering education… …   Wikipedia

  • Electrical element — Electrical elements are conceptual abstractions representing idealized electrical components, such as resistors, capacitors, and inductors, used in the analysis of electrical networks. Any electrical network can be analysed as multiple,… …   Wikipedia

  • electrical and electronics engineering — Introduction       the branch of engineering concerned with the practical applications of electricity in all its forms, including those of the field of electronics. Electronics engineering is that branch of electrical engineering concerned with… …   Universalium

Поделиться ссылкой на выделенное

Прямая ссылка:
Нажмите правой клавишей мыши и выберите «Копировать ссылку»