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 is not much but in some applications its enough to cause undesirable effects.Another common problem with air variables is dust and insects. Dust collected on the plates or a curious insect could have disastrous effects. An insect in contact with the plates is likely to cause a short circuit 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.
Read more about this topic: Vacuum Variable Capacitor
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