A feedthrough is a conductor used to carry a signal through an enclosure or printed

circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

. Like any conductor, it has a small amount of

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...

. A "feedthrough capacitor" has a guaranteed minimum value of built in it and is used for bypass purposes in ultra-high-frequency applications. Feedthroughs can be divided into power and instrumentation categories. Power feedthroughs are used to carry either high current or high voltage. Instrumentation feedthroughs are used to carry electrical signals (including

thermocouple A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the ...

s) which are normally low current or voltage. Another special type is what is commonly known as RF-feedthrough, specifically designed to carry very high frequency RF or

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...

electrical signals. A feedthrough electrical connection may have to withstand considerable pressure difference across its length. Systems that operate under high vacuum, such as

electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...

s, require electrical connections through the

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

. Similarly, submersible vehicles require feedthrough connections between exterior instruments and devices and the controls within the vehicle pressure hull. A very common example of a feedthrough connection is an automobile

spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...

where the body of the plug must resist the pressure and temperature produced in the engine, while providing a reliable electrical connection to the

spark gap A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductor ...

in the combustion chamber. (Spark plugs are occasionally used as low-cost or improvised feedthrough connections in non-engine applications.) There are electrical hermetically sealed feedthroughs for instrumentation, high amperage and voltage, coaxial, thermocouple and fiber optics. Rotary or mechanical feedthroughs also exist.

References

{{Reflist Electrical components de:Leistungstransformator#Durchf.C3.BChrungen

See also

References