了解测量单位。 看懂电容值。 找出容差值。 确定额定电压。 查找“+”号或“-”号。

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The base unit of capacitance is the farad (F). This value is much too large for ordinary circuits, so household capacitors are labeled with one of the following units:  1 µF, uF, or mF = 1 microfarad = 10-6 farads. (Careful — in other contexts, mF is the official abbreviation for millifarads, or 10-3 farads.) 1 nF = 1 nanofarad = 10-9 farads. 1 pF, mmF, or uuF = 1 picofarad = 1 micromicrofarad = 10-12 farads. Most large capacitors have a capacitance value written on the side. Slight variations are common, so look for the value that most closely matches the units above. You may need to adjust for the following:  Ignore capital letters in the units. For example, "MF" is just a variation on "mf." (It is definitely not a megafarad, even though this is the official SI abbreviation.) Don't get thrown by "fd." This is just another abbreviation for farad. For example, "mmfd" is the same as "mmf." Beware single-letter markings such as "475m," usually found on smaller capacitors.See below for instructions. Some capacitors list a tolerance, or the maximum expected range in capacitance compared to its listed value. This isn't important in all circuits, but you may need to pay attention to this if you require a precise capacitor value. For example, a capacitor labeled "6000uF +50%/-70%" could actually have a capacitance as high as 6000uF + (6000 * 0.5) = 9000uF, or as low as 6000 uF - (6000uF * 0.7) = 1800uF. If there is no percentage listed, look for a single letter after the capacitance value or on its own line. This may be code for a tolerance value, described below. If there is room on the body of the capacitor, the manufacturer usually lists voltage as a number followed by a V, VDC, VDCW, or WV (for "Working Voltage"). This is the maximum voltage the capacitor is designed to handle.  1 kV = 1,000 volts.  See below if you suspect your capacitor uses a code for voltage (a single letter or one digit and one letter). If there is no symbol at all, reserve the cap for low-voltage circuits only. If you are building an AC...