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An ESR meter is a two-terminal electronic measuring instrument designed and used primarily to measure the equivalent series resistance (ESR) of real capacitors; usually without the need to disconnect the capacitor from the circuit it is connected to. Other types of meter used for routine servicing, including normal capacitance meters, cannot be used to measure a capacitor's ESR, although a few combined meters are available which measure both ESR and out-of-circuit capacitance. A standard (DC) milliohmmeter cannot be used to measure ESR, because a steady direct current cannot be passed through the capacitor. Most ESR meters can also be used to measure non-inductive low-value resistances, whether or not associated with a capacitor; this leads to a number of additional applications described below. ==Need for ESR measurement== Aluminium electrolytic capacitors have a relatively high ESR that increases with age, heat, and ripple current; this can cause the equipment using them to malfunction. In older equipment, this tended to cause hum and degraded operation; modern equipment, in particular switch-mode power supplies, is very sensitive to ESR, and a capacitor with high ESR can cause equipment to malfunction or cause permanent damage requiring repair, typically by causing power supply voltages to become excessively high.〔(Example of high-ESR capacitors causing voltages to rise in a circuit and destroy components. ) High ESR capacitors cause "5V dropping quite low and causing every other voltage to go sky high (and doing things like frying the HDD with upwards of 15V rather than 12V, and frying the tuning agc transistor with upwards of 36V instead of 30V)."〕 This type of capacitor is very often used because it is inexpensive and has a very high capacitance per unit volume or weight; typically, these capacitors have capacitance from about one microfarad to tens of thousands of microfarads. Capacitors with faults leading to high ESR often bulge and leak, making them easy to identify visually; however, capacitors that appear visually perfect may still have high ESR, detectable only by measurement. Precise measurement of ESR is rarely necessary, and any usable meter is adequate for troubleshooting. Where precision is required, measurements must be taken under appropriately specified conditions, because ESR varies with frequency, applied voltage, and temperature. A general-purpose ESR meter operating with a fixed waveform is unlikely to be suitable for precise laboratory measurements. 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「ESR meter」の詳細全文を読む スポンサード リンク
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