Braid and Shield Calculations

Braid and Shield Coverage and Weight

 

Use this eight-step process to calculate the weight of braid or spiral shields based on your desired amount of shielding coverage. Keep the following guidelines in mind:

  • Recommended for the angle of shield to cable axis is 20 to 40º when diameters under shield (D) is 0.020-inches to 0.380-in, and 40 to 80º for D values greater than 0.380-in.
  • Rounded number of strands (N) is typically an integer value between 1 and 13.
Step 1. Convert desired coverage (%) into coverage factor (F).
Braid Shield

\[F = 1 - \sqrt {\frac{{100 - \% }}{{100}}} \]

Spiral Shield

\[F = \frac{\% }{{100}}\]

Step 2. Select angle of shield to cable in degrees (a) and calculate number of strands (N)
Braid Shield

\[N = \frac{{2\pi \cos (a)(D + 2d)F}}{{dC}}\]

Spiral Shield

\[N = \frac{{\pi \cos (a)(D + d)F}}{{dC}}\]

Step 3. Round number of strands (N) and recalculate angle (a)
Braid Shield

\[a = {\cos ^{.1}}\left( {\frac{{CNd}}{{2\pi (D + 2d)F}}} \right)\]

Spiral Shield

\[a = {\cos ^{.1}}\left({\frac{{CNd}}{{\pi (D + d)F}}} \right)\]

Step 4. Using new angle from Step 3, calculate picks per inch (P)
Braid Shield

\[P = \left( {\frac{{C\tan (a)}}{{2\pi (D + 2d}}}\right)\]

Spiral Shield

\[P = \frac{{C\tan (a)}}{{\pi (D + d)}}\]

Step 5. Round up picks per inch (P) to next increment, and recalculate angle (a).
Braid Shield

\[a = {\tan ^{.1}}\left({\frac{{2\pi P(D + 2d)}}{C}} \right)\]

Spiral Shield

\[a = {\tan ^{.1}}\left({\frac{{\pi P(D + d)}}{C}} \right)\]

Step 6. Recalculate coverage factor (F)
Braid Shield

\[F = \frac{{NPd}}{{\sin(a)}}\]

Spiral Shield

\[F = \frac{{NPd}}{{\sin(a)}}\]

Step 7. Recalculate coverage (%)
Braid Shield

\[\% = 100(2F - {F^2})\]

Spiral Shield

\[\% = 100F\]

Step 8. Calculate weight of shield in pounds per thousand feet (W).
Braid Shield

\[W = \frac{{1.03CNw}}{{\cos (a)}}\]

Spiral Shield

\[W = \frac{{1.03CNw}}{{\cos (a)}}\]

Read 16545 times Last modified on Wednesday, 01 January 2014 21:24
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