Resolver basics | resolver types | Resolver to Digital Converter

This page mentions basics of resolver to digital converter. It compares classical resolver vs variable reluctance resolver and mentions difference between them. The difference between resolver vs encoder is also mentioned.

Resolver definition:
• The rotary transformer device used to measure degrees of rotation is known as resolver.
• It has one primary and two secondary windings which are 90 degrees out of phase.
• This is shown in the figure-1.
• It is electro-mechanical device which converts mechanical motion into electronic signal.


Following are the technical specifications of resolver to be considered:
• Input voltage: The excitation voltage to primary winding (R1-R2).
• Input frequency: The excitation frequency to primary winding (R1-R2).
• Transformation Ratio: It is the ratio of amplitudes of primary winding and secondary winding.
• Input Impedance: It is the input impedance to resolver.
• Phase Shift in degrees: It is the phase shift between signal at primary winding (R1-R2) and signals at secondary windings (S3-S1 or S2-S4).
• Pole Pairs: The number of electrial rotations per mechanical rotation. Usually it will be 1-3.

Resolver vs Encoder

Following are the similarities and difference between resolver and encoder:
• Both are electro-mechanical devices.
• Resolver transmits analog signal while encoder transmits digital signal.

Resolver Types | classical resolver, variable reluctance resolver

Following are the two main types of resolver viz. classical and variable reluctance resolver.

classical resolver

Classical Resolver:
It consists of one primary winding on rotor and two secondary windings on stator. The figure-2 above depicts classical resolver.

variable reluctance resolver

Variable Reluctance Resolver:
It has no windings on rotor part. It consists of both primary winding and secondary winding on the stator itself. The figure-3 above depicts variable reluctance resolver.

Resolver to Digital Converter

• It is located between resolver and microcontroller/microprocessor.
• As mentioned primary winding of resolver is provided sine wave signal and it produces two differential outputs viz. sine and cosine at the secondary windings due to electro-mechanical process.
• Resolver to Digital converter uses sine and cosine signals in order to derive angular position as well as rotation speed of motor shaft.

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