The iron powder toroid cores (and also ferrite cores) are subject to large production tolerances which can be reflected in the Al value and can reach +/- 15%. The Q factor of the ring core coils and the permeability are strongly frequency-dependent. Furthermore, the geometry effect of the winding of the ring core has a great influence (see figure below). The practical value of the inductance can easily require a deviation from the theoretical calculated value of +/- 1 turns. Where it is practicable the compression or pulling of the winding is used for the fine adjustment.
If the ring cores are used in the RF filter range or for oscillating circuits where exact values are indispensable, then concrete measurements are usually essential for each core respectively winding - a sole calculation will provide unpleasant surprises!
 Toroidal Coils |
