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# Inductance Formula2

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## Inductance Formula

(OP)
I use program to caluculate inductance of core. But I would like to
know about equation. If I have following data:
- External Diameter of material, mm
- Inside Diameter (of hole), mm
- Thickness of ring, mm
- Wire Diameter, mm
- Number of turn of wire
- Permeability of core material (µ)
- Frequency, kHz.
How can I calculate it?

### RE: Inductance Formula

2
L=[(permeability of core mu) x (number of turns)**2 x (thickness of ring/2)**2]/[(external diameter + internal diameter)/2]
use m (meter) instead of mm (milimeter) to obtain correct value
where:
L is self-inductance of single-layer spaced toroidal coil (circular cross-sectional area)
mu = mu of air x relative mu of the material
mu of air = 4 (PI) 10E(-7)
mu of material is in per unit
valid for:
thickness of ring << internal diameter
close-winding
References:
1. "Electronic Products" - The Engineer's Magazine of Product Technology, July 2000, page 37
http://electronicproducts.com
2. Giacoletto L.J. "Electronics Designers' Handbook," Second Edition, McGraw-Hill, 1977, page 3-46 Table 3.8 (there is a little error in formula, namely, (thickness of ring/2) is not squared)

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