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What are Electrical Feedthroughs?


Electrical feedthroughs are components which enable the transfer of electrical power into or out of a hermetic chamber. Electrical feedthroughs consist of metal-ceramic-joints whereas the ceramic serves as an electrical insulator between the conductor and the connection flange. In addition to providing leak-tightness in high and ultra-high vacuum, many feedthroughs have to be resistant to high or cryogenic temperatures, high pressure and aggressive chemicals.


Coaxial Feedthroughs

Coaxial feedthroughs consist of two concentric conductor paths which are electrically isolated from each other by an alumina or glass-ceramic insulator in between. The inner pin-shaped conductor serves as current-carrying contact and is surrounded by a tubular outside conductor, which is usually at ground potential ("grounded shield"). The outer conductor shields the inner conductor from electromagnetic interference effects coming from outside. Coaxial feedthroughs can be used universally and are particularly applied for transmitting high-frequency signals up to 10 GHz and even beyond.


Thermocouple Feedthroughs

Thermocouple feedthroughs are widely used for temperature measurements in vacuum applications, whereas the temperature is not measured directly but can be calculated from a thermoelectric voltage. The thermoelectric voltage is generated due to charge separation (EMF) caused by a temperature difference between the two ends of an electrical conductor.


The thermoelectric voltage (depending on the conductor material) is nearly proportional to the temperature gradient. Thermocouples consist of two different electrically conductive materials connected at one end. Using thermocouple feedthroughs, the thermoelectric voltage (EMF) can be transmitted from the inside of a chamber to an external indicating instrument. A high thermoelectric voltage, corrosion resistance and linearity are decisive factors for the selection of the material combination. Noble and base metals as well as alloys - adapted to different applications - are combined in thermocouples. Typical alloys are Alumel (nickel, aluminium and manganese), Chromel (nickel and chrome) and constantan (copper and nickel).


Some thermocouple feedthrough types use compensating material ("compensating wire") instead of the actual thermocouple material. Compensating materials are characterised by thermoelectric properties ideally adapted to the corresponding thermocouple materials. For these types, we explicitly point out the use of compensating wire by footnotes ("Uses compensating wire"). 


Power & High Voltage Feedthroughs

Feedthroughs in this section provide the transmission of high voltage and/or high current into a hermetic chamber throughout a wide range of applications. The designs vary considerably depending on their technical specifications and requirements. The airside ceramic surface is mostly covered with a high-temperature glass coating in order to reduce surface contamination and to increase leakage current resistance.


The maximum transferable voltage is 100 kV, the maximum current is 800 A. On request, we also offer liquid-cooled high power feedthrough capable of handling up to 1000 A. Liquid-cooled feedthroughs are typically used with grounded, closed cooling systems and non-conductive coolants such as deionised water or ethylene glycol.

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