LYCOS RETRIEVER 
Capacitor: Plates
built 647 days ago
ESR (Equivalent Series Resistance) is an important parameter of any capacitor. It represents the effective resistance resulting from the combination of wiring, internal connections, plates, and electrolyte (in an electrolytic capacitor). The ESR affects the performance of tuned circuits (high ESR reduces the Q factor) and may result in totally incorrect or unstable operation of devices like switchmode power supplies and deflection circuits in TVs and monitors. As would be expected, electrolytic capacitors tend to have a high ESR compared to other types - even when new. However, due to the electrochemical nature of an electrolytic capacitor, the ESR may indeed change - and not for the better - with time. When troubleshooting electronic equipment, electrolytic capacitors, in particular, may degrade resulting in a significant and unacceptable increase in ESR without a similar reduction in uF capacity when measured on a typical DMM's capacitance scale or even a cheap LCR meter. There commercial ESR meters and kits available ranging from $50 to $200 or more.
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The first capacitor was the Leyden jar, invented at the Netherlands University in the 17th century. This type of capacitor consists of a glass jar coated with metal on the inside and outside. A rod is connected to the inner coat of metal, passed through the lid of the capacitor, and topped off with a metal ball. As with all capacitors, the Leyden jar contains an oppositely charged electrode and a plate that is separated by an insulator. The Leyden jar has been used to conduct experiments in electricity for hundreds of years.
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The current through a capacitor due to an AC source reverses direction periodically. That is, the alternating current alternately charges the plates: first in one direction and then the other. With the exception of the instant that the current changes direction, the capacitor current is non-zero at all times during a cycle. For this reason, it is commonly said that capacitors "pass" AC. However, at no time do electrons actually cross between the plates, unless the dielectric breaks down. Such a situation would involve physical damage to the capacitor and likely to the circuit involved as well.
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In October 1745, Ewald Georg von Kleist of Pomerania invented the first recorded capacitor: a glass jar coated inside and out with metal. The inner coating was connected to a rod that passed through the lid and ended in a metal sphere. By having this thin layer of glass insulation (a dielectric) between two large, closely spaced plates, von Kleist found the energy density could be increased dramatically compared with the situation with no insulator.
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As you know th at the capacitor is made by placing insulating material between the two conductive plates, this insulating material is known as dielectric material. A good dielectric material is that one in which there is no loss of energy given by an electric field across the dielectric. The dielectric due to which there is a loss in the energy of the electric field in the form of heat is not a good dielectric material. Capacitors are named according to the type of dielectric material used. On the basis of the dielectric material capacitor can be divided in two types:
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Multiple layers of the metalized plastic material make up the capacitor. Adding layers or increasing the size of the layers (without increasing the thickness of the layers) will increase capacitance. The following diagram is an incredibly generic film capacitor. You can see the dark blue insulating film between the cyan and violet plates. The plates are soldered to one of the terminals on one end of the plates. Half of the plates are soldered to terminal A and the other half of the plates are soldered to terminal B.
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