Triaxial cable
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Triaxial cable, often referred to as triax for short, is a type of electrical cable similar to
coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
, but with the addition of an extra layer of insulation and a second conducting sheath. It provides greater
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
and rejection of interference than coax, but is more expensive.


Applications


Television production

The most common use of triaxial cable is in television industry as a connecting cable between a
camera A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...
and its
camera control unit The camera control unit (CCU) is typically part of a live television broadcast chain. It is responsible for powering the professional video camera, handling signals sent over the camera cable to and from the camera, and can be used to control ...
(CCU). The outer sheath is commonly used as a protective earth conductor. The core provides both power and signal connections, with the return for the power being provided through the inner screen. Through frequency-division
multiplexing In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
, the camera can send audio and video signals along the triax while the CCU can send camera control information, such as exposure settings, intercom, return audio and video (usually that of the program), and tally (a signal alerting the operator that their camera is on the air). Venues that host television productions fairly often, such as sports arenas, will usually have triaxial cables run from the location of the TV truck to common camera locations throughout the building. This is convenient for visiting television crews, who can simply plug into existing cable runs instead of having to run their own cables and remove them after the broadcast. *In 1992 N.V.
Philips Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters i ...
,
Breda Breda () is a city and municipality in the southern part of the Netherlands, located in the province of North Brabant. The name derived from ''brede Aa'' ('wide Aa' or 'broad Aa') and refers to the confluence of the rivers Mark and Aa. Breda has ...
received the Outstanding Achievement in Technical/Engineering Development Award from the
National Academy of Television Arts & Sciences The National Academy of Television Arts and Sciences (NATAS) is an American professional service organization founded in 1955 for "the advancement of the arts and sciences of television and the promotion of creative leadership for artistic, edu ...
for Triaxial cable Technology for Color Television Cameras. Also see
Norelco Norelco is the American brand name for electric shavers and other personal care products made by the Consumer Lifestyle division of Philips. For personal care products marketed outside the United States, Philips used the Philishave trademark unti ...
and BTS


Decline of triax in television

With the increasing bandwidth requirements of developments such as 4K/
UHDTV Ultra-high-definition television (also known as Ultra HD television, Ultra HD, UHDTV, UHD and Super Hi-Vision) today includes 4K UHD and 8K UHD, which are two digital video formats with an aspect ratio of 16:9. These were first proposed by ...
, HFR (
high frame rate In motion picture technology—either film or video—high frame rate (HFR) refers to higher frame rates than typical prior practice. The frame rate for motion picture film cameras was typically 24 frames per second (fps) with multiple flashes on ...
) and HDR (
high dynamic range High dynamic range (HDR) is a dynamic range higher than usual, synonyms are wide dynamic range, extended dynamic range, expanded dynamic range. The term is often used in discussing the dynamic range of various signals such as images, videos, au ...
) the use of triax is declining in the TV industry. Most of the recently developed broadcast cameras from the leading manufacturers have hybrid single-mode fibre and copper power cores which supersede the older triax connectivity. The advantages of the hybrid copper/fibre over triax cable are noise immunity due to the optical isolation and extremely high bandwidth.


Current measurements

Another application for triaxial cables is for probes taking precision low-current measurements where the leakage current through the insulator between the core and shield would normally alter the measurements. The core (known as the force) and the inner shield (known as the guard) are kept at approximately the same electrical potential by a voltage buffer/follower, thus the leakage current between them is zero for all practical purposes, despite the imperfections of the insulation. Instead, the leakage current occurs between the inner and outer shields, which does not matter since that current will be supplied by the buffer circuit rather than the
device under test A device under test (DUT), also known as equipment under test (EUT) and unit under test (UUT), is a manufactured product undergoing testing, either at first manufacture or later during its life cycle as part of ongoing functional testing and calibra ...
and will not affect measurements. This technique can provide almost perfect elimination of leakage current but becomes less effective at very high frequencies as the buffer cannot follow the measured voltage accurately.


See also

*
Twinaxial cabling Twinaxial cabling, or "Twinax", is a type of cable similar to coaxial cable, but with two inner conductors instead of one. Due to cost efficiency it is becoming common in modern (2013) very-short-range high-speed differential signaling application ...
*
Coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...


References

Signal cables Transmission lines {{telecomm-stub