LYCOS RETRIEVER 
Capacitor: Capacitors
built 659 days ago
Capacitor banks applied within distribution substations typically consists of one to four banks of switched capacitors as shown in Figure 1 (which shows a three step switched bank). The switched banks are designed to come on and off automatically based on power factor, vars, and/or voltage. Due to load variations, a number of switching operations will occur daily. Each switching event is followed by a low-frequency decaying ring wave transient that can result in power quality problems for nearby industrial and commercial loads.
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Capacitor microphones are able to respond to very high audio frequencies, and they are usually much more sensitive than their dynamic counterparts. In other words, they require less amplification than dynamic models to produce the same output level from the same signal source, making them more suitable for quieter or distant sound sources. The reason capacitor microphones have such a good f
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I've had the displeasure of owning one of the Abit boards with a burst capacitor, although it had given good service over its somewhat abbreviated lifetime. Apparently this problem stretches way back to even 2001, when Gary Headlee first started noticing an influx of boards with failed capacitors. Gary runs a motherboard repair service, and one of the services he offers is replacement of failed caps. Gary noted a large number of Abit boards, all with burst caps. Many tried in vain to get Abit to acknowledge the problem, and Abit did so only after a very concerted effort on the part of consumers. Gary did have more info on other motherboard brand failures, but lawyers from the various firms descended upon him and forced removal of his information.
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Time Constant: A capacitor's time constant is the time it takes for the capacitor to charge to 63.2% of the supply voltage when charged through a given resistor. At the end of one time constant, if the supply voltage is 10 volts, the capacitor will have charged to 6.32 volts. A capacitor is condidered to be fully charged after 5 time constants. After 5 time constants, the capacitor will have charged to 99.2% of the supply voltage. The following chart shows the charging curve for a 1 farad capacitor and a 50 ohm resistor. As you can see, the capacitor charges more quickly at first and then (as the difference between the capacitor's voltage and the supply's voltage is reduced) the rate of charge slows.
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The invention of the capacitor varies somewhat depending on who you ask. There are records that indicate a German scientist named Ewald Georg von Kleist invented the capacitor in November 1745. Several months later Pieter van Musschenbroek, a Dutch professor at the University of Leyden came up with a very similar device in the form of the Leyden jar, which is typically credited as the first capacitor. Since Kleist didn't have detailed records and notes, nor the notoriety of his Dutch counterpart, he's often overlooked as a contributor to the capacitor's evolution. However, over the years, both have been given equal credit as it was established that their research was independent of each other and merely a scientific coincidence [source: Williams].
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Conventional capacitor mics are very high-impedance devices, so any condensation on the capsule will affect electrical performance quite noticeably. This can be a problem when taking a mic from a cool locker and then having somebody sing into it at close range. What tends to happen is that the sensitivity of the mic falls off and irregular background noises such as pops or crackles start to appear. Using a pop shield will help, but it's important to make sure the mics are at room temperature before use, and to ensure that the room isn't cold enough to permit condensation. In extreme cases, the mic may have to be withdrawn from service for a short while and placed somewhere warm to dry out. Note that RF capacitor mics, such as the Sennheiser MKH series, don't tend to suffer from this problem.
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