Capacitors Blog

In analog computers, high precision potentiometers are used to scale intermediate results by desired constant factors, or to set initial conditions for a calculation. A motor-driven potentiometer may be used as a function generator, using a non-linear resistance card to supply approximations to trigonometric functions. For example, the shaft rotation might represent an angle, and the voltage division ratio can be made proportional to the cosine of the angle.

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Photo: Inside, an electrolytic capacitor is a bit like a Swiss roll. The "plates" are two very thin sheets of metal; the dielectric an oily plastic film in between them. The whole thing is wrapped up into a compact cylinder and coated in a protective metal case.

Warning: It can be dangerous to open up capacitors. First, they can hold very high voltages. Second, the dielectric is sometimes made of toxic or corrosive chemicals that can burn your skin.

A capacitor is a bit like a battery, but it has a different job to do. A battery uses chemicals to store electrical energy and release it very slowly through a circuit—sometimes (in the case of a quartz watch) it can take several years. A capacitor generally releases its energy much more rapidly—often in seconds or less. If you're taking a flash photograph, for example, you need your camera to produce a huge burst of light in a fraction of a second. A capacitor attached to the flash gun charges up for a few seconds using energy from your camera's batteries. (It takes time to charge a capacitor and that's why you typically have to wait a little while to take a flash photo.) Once the capacitor is fully charged, it can release all that energy in an instant through the xenon flash bulb. Zap!

Capacitors come in all shapes and sizes, but they usually have the same basic components. There are the two conductors (known as plates, largely for historic reasons) and there's the insulator in between them (called the dielectric). The two plates inside a capacitor are wired to two electrical connections on the outside called terminals, which are like thin metal legs you can hook into an electric circuit.

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----All Kinds of Capacitors 

When clouds drift through the sky, ice particles inside them rub against the air and gain static electrical charges—in just the same way that a balloon gets charged up when you rub it on your jumper. The top of a cloud becomes positively charged when smaller ice particles swirl upward (1); the bottom of a cloud becomes negatively charged when the heavier ice particles gather lower down (2). The separation of positive and negative charges in a cloud makes a kind of moving capacitor!

As a cloud floats along, the electric charge it contains affects things on the ground beneath it. The huge negative charge at the bottom of the cloud repels negative charge away from it, so the ground effectively becomes positively charged (3). The separation of charge between the bottom of the cloud and the ground beneath means that this area of the atmosphere is also, effectively, a capacitor.

Over time, enormous electrical charges can build up inside clouds. If the charge is really big, the cloud contains an enormous amount of electrical potential energy (it has a really high voltage). When the voltage reaches a certain level (sometimes several hundred million volts), the air is transformed from being an insulator into a conductor, and electricity will flow through it as though it were a metal wire, creating a giant spark better known as a bolt of lightning (4). The cloud behaves like a flash gun in a camera: the huge electrical energy stored in its "capacitor" is discharged in an instant and converted into a flash of light.

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----All Kinds of Capacitors

The size of a capacitor is measured in units called farads (F), named for English electrical pioneer Michael Faraday (1791–1867). One farad is a huge amount of capacitance so, in practice, most of the capacitors we come across are just fractions of a farad—typically microfarads (thousandths of a farad, written μF), nanofarads (thousand-millionths of a farad written nF), and picofarads (million millionths of a farad, written pF). Supercapacitors store far bigger charges, sometimes rated in thousands of farads.

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----All Kinds of Capacitors

When reading schematics, repairing radios and buying capacitors, you often must convert between uF, nF and pF.

Paper and electrolytic capacitors are usually expressed in terms of uF (microfarads). Short forms for micro farad include uF, mfd, MFD, MF and UF. Mica capacitors are usually expressed in terms of pF (micromicrofarads) (picofarads).

Short forms for micromicrofarads include pF, mmfd, MMFD, MMF, uuF and PF. A pF is one-millionth of a uF. In between a pF and a uF is a nF which is one-one thousands of a uF. Converting back and forth between uF, nF and pF can be confusing with all those darn decimal points to worry about. Below is a uF - nF- pF conversion chart.

+/-5%(J), +/-10%(K), +/-20%(M)The letter after the marking often indicates the tolerance.

Example:101K would be 100pf, +/-10%

When You Are Tired, Do You Get a Headache Converting Picofarads to Microfarads?
Maybe this will help you.

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3mm trimmer capacitor       
5mm trimmer capacitor      
6mm trimmer capacitor
7mm trimmer capacitor

Please visit our website: www.suntan.com.hk and send us email to info@capacitors.com.hk if you have any inquire.

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----All Kinds of Capacitors

A vacuum variable capacitor uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating and/or capacitance value using a smaller total volume. In addition to the higher voltage rating a vacuum dielectric greatly reduces the chance of arcing between the plates. There are several different designs in vacuum variables, the most common geometry of the capacitor plates is usually inter-meshed concentric cylinders. The meshed cylinders are contained within a glass or ceramic vacuum envelope, similar to an electron tube. A metal bellows is used to maintain a vacuum seal while allowing positional control for the moving parts of the capacitor.

Common Applications

Vacuum variable capacitors are commonly used in high voltage applications 5000 volts(5kV) and above. They are used in equipment such as high powered broadcast transmitters, Amateur radio RF Amplifiers and large Antenna tuners.

Other Variations

A fixed value vacuum capacitor. Other variations of vacuum capacitors include fixed value capacitors. Fixed value capacitors are designed very much like the variable versions with the exception of an adjustment mechanism.

Comparison

When compared to other variable capacitors vacuum variables tend to be more precise and more stable. This is due to the vacuum itself. Because of the sealed chamber the dielectric constant remains the same over a wider range of operating conditions. With air Variable capacitors the air moving around the plates may change the value slightly; often it’s not much but in some applications is enough to cause undesirable effects. Another common problem with air variables is dust and insects. Dust collected on the plates or a curious insect can raise havoc. A wandering spider is bound to make fireworks with the open frame design used on most air variable capacitors.

Vacuum variable capacitors are generally more expensive than Air Variable Capacitors this is primarily due to their design and the materials used. Although most use copper and glass some may use other materials such as ceramics and metals such as gold and silver. Vacuum variables also vary in adjustment mechanisms which range from course to fine.

Suntan is a Hong Kong based manufacturer of Ceramic Capacitors. Including High Voltage Ceramic Capacitors, Multilayer Ceramic Capacitors, Ceramic Disc Capacitor, Mini Type Ceramic Capacitors etc.

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----All Kinds of Capacitors

Suntan pictures of Capacitors. Notice that all these capacitors have two wires coming out of them, one attached to each plate.

Suntan is well established and specializes in service and quality with an extensive export and import network. We provide quick turn around for our customers all over the world. Almost 30 years experience with all types of passive components using good materials, state of the art equipment and technology and ongoing QC coupled with extensive R & D assure our customers of the best quality and on time delivery.

Suntan offer many kinds of capacitors. Don’t hesitate to send us inquire to sales@suntan.com.hk .We will show you good quality and best price.