Operating Principles

Inductive Coupling Between Precision Windings

Precision circuit patterns are etched in copper bonded to the surface of InductosynŇ elements.  For rotary Inductosyns, the printed circuit pattern comprises hairpin radial turns which repeat on the flat surface of a disk.  For linear Inductosyns, the printed circuit pattern comprises parallel hairpin turns which repeat along the surface of a flat bar.   The length of one complete cycle of the hairpin patterrn is called the pitch (P).   See Figure 1A. 

Inductive coupling between windings on a rotary or linear pair of elements is used to measure displacement.  The inductosyn elements are attached to the fixed and moveable machine parts with the elements aligned so that their winding patterns are mutually parallel and separated by a small air gap.

72windings.JPG (63426 bytes)
In Figures 1A, 1B, and 1C, winding W2 moves relative to stationary winding W1.  Application of an AC excitation signal, V1, to the winding on one element will cause a current flow in that winding which simultaneously induces a corresponding current flow and output voltage, V2, in the winding of the second element.  See Figure 1A.   The amplitude and phase of this induced voltage depends on the relative positions of the winding conductors.  In Figure 1A, the induced voltage V2 is at maximum amplitude when the winding conductors W2 of one element are exactly aligned with the winding conductors W1 of the other element.

In Figure 1B, the induced voltage, V2, passes through zero when the winding conductors, W2, of one element are midway between the winding conductors, W1, of the other element.  The distance moved by W2, from the position shown in Figure 1A to that shown in Figure 1B, is P/4.

In Figure 1C, the induced voltage reaches a maximum amplitude of opposite phase when the winding conductors of both elements are in their next exactly aligned position.  For simplicity, the phase reversal is shown as a change in polarity in Figure 1C.  The signal forms shown in the circles in Figure 1 are indicative of those that would be observed on an oscilloscope connected to the output winding.  Winding W2 moved a distance P/2, between the positions shown in Figures 1A and 1C.


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Last modified:
February 17, 2021