I need help with a computaion I can't seem to resolve. Essentially the linear measurement of each individual wire in twisted pair. The question at 2 complete twists per inch. 17.5 inches in length finished, how long are the individual conductors with a OD of 0.0574 inch / radius of 0.00853?
Helix linear measurement.
- Thread starter Kabooki
- Start date
Dr.Peterson
Elite Member
- Joined
- Nov 12, 2017
- Messages
- 16,749
Some clarification is needed. I assume your OD is for each wire; what does the radius refer to?
Generally, to find the length of a wire in a helix, you multiply the length of the helix by the ratio of the hypotenuse to the height of a right triangle at the same angle as the wire. That is, the vertical leg of the triangle in your case would be 1/2 inch (the length for one twist), and the horizontal leg would be the circumference of the cylinder around which it is wrapped.
The trick is to be sure what cylinder to think of the wires as being wrapped around; in theory that will be the same radius as the wire, because the center of the wire would be that far from the center of the helix; but I doubt that would be really accurate.
Here is a discussion of this problem. In practice, I'd probably want to take a sample of such a twisted pair, may 10 inches, unwind it and measure the length of one wire (say, 11 inches), and then use that ratio (so that a 100-foot length would require 11/10 * 100 = 110 feet of wire. I suspect that's an exaggerated example!
On the other hand, since you plan only a short length, the formula can give you a good enough estimate.