Publish Date: Dec 05, 2006 | 67 Ratings | 3.46 out of 5 | Print


A resolver is an absolute position feedback device which operates as described below.

The stator is made up of two windings, winding A and winding B. Winding A is positioned at a right angle to winding B. The rotor is made up of a third winding, winding C. This is energized with a sinusoidal voltage and allowed to rotate. The signal in winding C induces a signal in both windings A and B. Rotating winding C causes the magnitude of the induced signals to vary as a function of the angular position. The voltage induced in A is in quadrature to the voltage induced in B. Each position along the rotation produces a different value for the combination of A and B. This is illustrated in the following image:

Output from phase A is typically Vi * sin(wt + ph) and the output from phase B is typically Vi * cos( wt + ph). Where
Vi = Voltage in
w = Angular frequency
t = time
ph = phase shift

Using the output of the two windings gives an absolute position, since each position has a different combination of A and B. The frequency also changes with the velocity, the velocity can also be determined.

The data output from the two phases is usually converted from analog to digital by means of a resolver-to-digital converter.

You can typically achieve a resolution up to 65,536 counts per revolution using resolvers.

Currently, resolvers cannot be used to control motors with NI motion control products except as described in the related link, "Absolute Encoders and NI Products".
See Also:
Absolute encoders and NI products

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