Triaxial Cable, often referred to as triax for short, is a type of electrical cable similar to coaxial cable, but with the addition of an extra layer of insulation and a second conducting sheath. It provides greater bandwidth and rejection of interference than coax, but is more expensive. It is most commonly used in the television industry as a connecting cable between a camera and its 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, 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 his/her camera is on the air) as well as power for the camera.
Venues which host television productions fairly often such as sports arenas will usually have triax run from the location of the TV truck to common camera locations throughout the building. This allows a shorter and easier workday for visiting television crews who can simply plug into existing cable runs instead of having to run their own and tear them down after the shoot.
In 1992 N.V. Philips, Breda received the Outstanding Achievement in Technical/Engineering Development Award from the National Academy of Television Arts & Sciences for Triaxial cable Technology for Color Television Cameras. Also see Norelco and BTS
Another area where triaxial cables are used is precision low-current measurements. The core and the inner shield (guard) are kept at the same potential, thus the leakage current between them is zero for all practical purposes, despite the imperfections of the insulation. Instead, the leakage occurs between the inner and outer shields, which does not matter, because it is the core that is connected to the device under test and the core current is being measured.
Triaxial cable can be used with Triax domestic distribution equipment to allow it to carry a multitude of signal types, including combining and splitting the signals again.
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