Resolver - SDM Magnetics Co., Ltd.

Ι What Are Resolvers?

A resolver serves as a rotary electrical transformer or sensor, measuring angular displacement and speed of rotating objects. It operates as an analogue device with digital equivalents. Structurally, a resolver often mirrors an electric motor, featuring copper windings on the stator and a machined metal rotor. This design makes it ideal for applications needing precise rotational measurements, such as robotics, aerospace, and industrial machinery, where accuracy is critical.

Renowned for their precision, reliability, and robustness, resolvers excel in harsh environments. They resist electrical noise and operate across a broad temperature range. Additionally, with no contact parts, a resolver ensures a prolonged operational life. Its adaptability and strong performance suit demanding applications, delivering accurate, dependable measurements under challenging conditions across various industries.

Working Principle of Resolver

A resolver functions using electromagnetic induction principles. It comprises a stator (stationary part) and a rotor (rotating part), each equipped with windings. An AC voltage energizes the stator’s primary winding, producing an electromagnetic field. As the rotor rotates within this field, its windings generate secondary voltages depending on their position relative to the stator, enabling precise position detection through the resolver’s operation.

The resolver produces two output signals—sine and cosine—that change with the rotor’s position; the sine signal reflects the sine of the rotation angle, while the cosine signal mirrors the cosine. These signals feed into resolver-to-digital converters (RDCs), which calculate the exact angular position. The sine-to-cosine ratio offers a precise angle measurement, converting mechanical rotation into electrical signals for accurate interpretation.

Resolver vs. Encoder: Key Differences and Uses

A resolver and an encoder both measure rotary motion and speed, yet a resolver operates differently from an encoder. The distinctions between a resolver and an encoder are explored below.

Type	Resolvers	Encoders
Operating principle	Use rotary transformers to generate analog signals.	Use optical, magnetic, or capacitive sensing techniques.
Signal output	Analog.	Digital.
Resolution and accuracy	Generally robust but may have lower resolution compared to high-end encoders.	High resolution and accuracy, especially absolute encoders.
Environmental robustness	Highly robust, suitable for harsh environments.	Sensitive to dust, dirt, and temperature variations, especially optical encoders.
Complexity	More complex due to the need for analog-to-digital conversion, requiring detailed parameter considerations.	Simpler to integrate, providing digital signals directly without additional conversion.
Flexibility	Less flexible, harder to upgrade, requiring comprehensive re-evaluation.	More flexible, easier to upgrade by replacing components and updating software.
Cost	Generally higher.	Generally lower, varies by type.

Specifications of Variable Reluctance Resolvers

Number of pole	2X	3X	4X
Outside diameter of stator	ø37mm/ø52mm/ø65mm/ø74mm/ø101mm
Input voltage	AC 7Vrms
Input frequency	10kHz
Transformer ratio	0.286±10%
Operating temperature range	-40 to 150 degrees Celsius
Electrical error	±60′	±45′	±30′
Phase shift	0°±15°
Input impedance	75 to 150Ω (customizable as per requirements)

2025-11-21 Rare Earth Price Info
November 21, 2025