How to measure the length of metal sheet coil?

[qnikchen]

Hi everyone,

I have been trying to find an equation to measure the length of a coil. The coil is a metal sheet that wraps around the loops as it creates. It looks like a roll of tape. I have been using two different formula, but it is not giving me the right results.

1. L = 0.065449 (OD^2 - ID^2) / T; where OD is the outer diameter, ID the inner diameter, and T the thickness of the sheet.

2. L = ((ID + OD)/2 X 3.14 * # of wraps on the coil )/12.

I am not sure if I am using the right formula, but can some please give me a hint on this?

Thank you

 

[Dr.D]

Where did you get those equations? Did you derive them?

 

[qnikchen]

Hi Dr. D.

Those are found online. Both formulas takes the number in inches, and convert them in feet.

 

[Dr.D]

To get a better result andto gain more understanding, try working the problem from first principles using integration.

 

[Baluncore]

... where OD is the outer diameter, ID the inner diameter, and T the thickness of the sheet.

The area of metal at the end of the roll is; Area = (π * (OD/2)²) – (π * (ID/2)²)
Therefore, Area = π/4 * ( OD² – ID² )

The length of the coil will be Area / T
Therefore, Length = π/4 * ( OD² – ID² ) / T

The 0.065449 in your first equation is π/4, divided by twelve to convert from inches to feet.

 

[Low-Q]

Hi everyone,

I have been trying to find an equation to measure the length of a coil. The coil is a metal sheet that wraps around the loops as it creates. It looks like a roll of tape. I have been using two different formula, but it is not giving me the right results.

1. L = 0.065449 (OD^2 - ID^2) / T; where OD is the outer diameter, ID the inner diameter, and T the thickness of the sheet.

2. L = ((ID + OD)/2 X 3.14 * # of wraps on the coil )/12.

I am not sure if I am using the right formula, but can some please give me a hint on this?

Thank you

L=[square root (OD^2 - ID^2)] x PI x turns

turns= (OR-IR)/foil thickness
Remember that most foil coils do have a foil of insolation parallell with the copper foil (If it is intended to be an inductor. So foil thickness should be both combined.

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