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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Dissipation factor ： ウィキペディア英語版 Dissipation factor In physics, the dissipation factor (DF) is a measure of loss-rate of energy of a mode of oscillation (mechanical, electrical, or electromechanical) in a dissipative system. It is the reciprocal of quality factor, which represents the "quality" or durability of oscillation. ==Explanation== Electrical potential energy is dissipated in all dielectric materials, usually in the form of heat. In a capacitor made of a dielectric placed between conductors, the typical lumped element model includes a lossless ideal capacitor in series with a resistor termed the equivalent series resistance (ESR) as shown below.〔http://www.cartage.org.lb/en/themes/sciences/physics/electromagnetism/electrostatics/Capacitors/Applications/BasicConsiderations/BasicConsiderations.htm〕 The ESR represents losses in the capacitor. In a good capacitor the ESR is very small, and in a poor capacitor the ESR is large. However, ESR is sometimes a minimum value to be required. Note that the ESR is ''not'' simply the resistance that would be measured across a capacitor by an ohmmeter. The ESR is a derived quantity with physical origins in both the dielectric's conduction electrons and dipole relaxation phenomena. In a dielectric only one of either the conduction electrons or the dipole relaxation typically dominates loss.〔S. Ramo, J.R. Whinnery, and T. Van Duzer, ''Fields and Waves in Communication Electronics'', 3rd ed., (John Wiley and Sons, New York, 1994). ISBN 0-471-58551-3〕 For the case of the conduction electrons being the dominant loss, then $\backslash text\; =\; \backslash frac$ where : $\backslash sigma$ is the dielectric's bulk conductivity, : $\backslash omega$ is the angular frequency of the AC current ''i'', : $\backslash varepsilon$ is the lossless permittivity of the dielectric, and : $C$ is the lossless capacitance. If the capacitor is used in an AC circuit, the dissipation factor due to the non-ideal capacitor is expressed as the ratio of the resistive power loss in the ESR to the reactive power oscillating in the capacitor, or $\backslash text\; =\; \backslash frac\; |\}\; =\; \backslash omega\; C\; \backslash cdot\; \backslash text\; =\; \backslash frac\; =\; \backslash frac$ When representing the electrical circuit parameters as vectors in a complex plane, known as phasors, a capacitor's dissipation factor is equal to the tangent of the angle between the capacitor's impedance vector and the negative reactive axis, as shown in the diagram to the right. This gives rise to the parameter known as the loss tangent ''δ'' where $\backslash tan\backslash delta\; =\; \backslash frac\; =\; \backslash text$ Since the ''DF'' in a good capacitor is usually small, ''δ'' ~ ''DF'', and ''DF'' is often expressed as a percentage. ''DF'' approximates to the power factor when $\backslash text$ is far less than $X\_c$, which is usually the case. ''DF'' will vary depending on the dielectric material and the frequency of the electrical signals. In low dielectric constant (low-k), temperature compensating ceramics, ''DF'' of 0.1% to 0.2% is typical. In high dielectric constant ceramics, ''DF'' can be 1% to 2%. However, lower ''DF'' is usually an indication of quality capacitors when comparing similar dielectric material. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dissipation factor」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.