A feedthrough is a conductor used to conduct a signal through a printed circuit board. Like any conductor it has a small amount of capacitance

Capacitance

In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

. It is used mainly to bypass purposes in ultra-high-frequency circuits. There are many different types of feedthrough but they can be divided into two categories; Power, and Instrumentation. Power feedthroughs are used to carry either high current, or high voltage, or both. Instrumentation feedthroughs are used to carry electrical signals (including thermocouples) which are normally low current and/or voltage.

Use

Electrical feedthroughs will give long and reliable service if they are properly treated. They must be stored carefully and kept free from damage. It is important not to exceed the feedthrough temperature and power ratings as this can damage the feedthrough, or cause vacuum leaks.