Can anyone tell me what triax cable is good for.

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Discussion Overview

The discussion revolves around the applications and characteristics of triaxial cable, particularly in contexts such as video signal transmission, grounding issues, and high impedance measurements. Participants explore its shielding properties and potential advantages over standard coaxial cables.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that triax cable is unbalanced and questions its suitability for differential transmission, expressing confusion about the differences between single and double shielding.
  • Another participant shares personal experiences using triax cable for grounding issues, explaining how the outer shield can ground equipment while the inner shield carries a single point ground.
  • A different participant discusses the multifunctional role of coax shields and highlights that triax allows for separation of signal reference from other functions to reduce noise.
  • One participant mentions that triax is evidently used for video signals, linking it to specific applications like CCTV cameras where power and signal share the same cable.
  • Another participant suggests consulting the "Low Level Measurements Handbook" from Keithley for more information on triax applications, indicating that it is used in various instruments.
  • One participant states that triax cables are used for gate circuits to measure high impedance sources.

Areas of Agreement / Disagreement

Participants express various applications and characteristics of triax cable, but there is no consensus on its overall advantages or specific use cases. Multiple competing views and interpretations of its functionality remain present in the discussion.

Contextual Notes

Some claims about the use of triax cable depend on specific applications and contexts, such as grounding needs or video signal transmission, which may not be universally applicable. The discussion also reflects uncertainty regarding the technical distinctions between shielding types.

Who May Find This Useful

Individuals interested in cable technology, video signal transmission, grounding techniques, and high impedance measurement applications may find this discussion relevant.

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Can anyone tell me what triax cable is good for. As far as I understand it, it is unbalanced so you cannot use it for differential transmission, and I don't understand how there is supposed to be a difference between single and double shielding.
 
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I have used triax coaxial cable in two different situations. 1) When I have serious grounding problems, the outer shield is used to ground equipment together, and the inner shield is used to carry a single point ground, like at a pre-amplifier. Also, wrapping a few turns of coax around a hi-mu toroid will help. 2) When I need to feed a signal back from an amplifier to a coax shield from a sensitive pickup to reduce the effective cable capacitance, I can feed it back on the inner shield, and use the outer shield for ground.
 


In coax, the shield serves multiple purpose like signal reference/return, Earth ground for safety, electromagnetic shielding. With triax you can separate the signal reference from the other functions when you can't tolerate the noise they introduce.

They might help in cases where you care about other cable problems like triboelectric charge depending on cable materials and construction too.
 


The reason why triax is sometimes used from video is -as far as I remember- that some devices (presumably things like CCTV cameras) are powered using the same cable as for the signal; i.e. one if the shields is actually carrying a current.

Anyway, if you want to know more about triax I would suggest getting (it is free) the "Low Level Measurements Handbook" from Keithley; they use triax for a lot of their instruments and as far as I remember they explain the reasons quite well in that book.
 


f95toli said:
[...]
Anyway, if you want to know more about triax I would suggest getting (it is free) the "Low Level Measurements Handbook" from Keithley; they use triax for a lot of their instruments and as far as I remember they explain the reasons quite well in that book.

Thanks. That book is floating around somewhere here, I'll give it a try...
 


That was easy, they are used for gate circuits to measure high impedance sources.
 

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