RESOLVER CONTROL TRANSMITTER

A resolver is a rotary transformer where the magnitude of the energy through the resolver windings varies sinusoidally as the shaft rotates. A resolver control transmitter has one primary winding, the Reference Winding, and two secondary windings, the SIN and COS Windings. (See figure 1.1, Resolver Cross Section). The Reference Winding is located in the rotor of the resolver, the SIN and COS Windings in the stator. The SIN and COS Windings are mechanically displaced 90 degrees from each other. In a brushless resolver, energy is supplied to the Reference Winding (rotor) through a rotary transformer. This eliminates brushes and slip rings in the resolver and the reliability problems associated with them.

In general, in a control transmitter, the Reference Winding is excited by an AC voltage called the Reference Voltage (Vr). (See figure 1.2, Resolver Schematic). The induced voltages in the SIN and COS Windings are equal to the value of the Reference Voltage multiplied by the SIN or COS of the angle of the input shaft from a fixed zero point. Thus, the resolver provides two voltages whose ratio represents the absolute position of the input shaft. (SIN θ / COS θ = TAN θ, where θ = shaft angle.) Because the ratio of the SIN and COS voltages is considered, any changes in the resolvers’ characteristics, such as those caused by aging or a change in temperature, are ignored. An additional advantage of this SIN / COS ratio is that the shaft angle is absolute. Even if the shaft is rotated with power removed, the resolver will report its new position value when power is restored.