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Basics: Resolver

Matthias Beetz, Baumüller Nürnberg GmbH

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Resolver basics

The Resolver is a measuring instrument that is used to determine the angular position and speed of a rotor. It is a particularly robust type of angle transmitter. It sits directly on the shaft of the motor and records its rotation. The position of the rotor within the resolver corresponds to the angular position in the motor. By communication with a servo-controller, permanent synchronization takes place between the set and actual values with regard to the speed and position of the motor. In this respect, the resolver provides the data basis, on the basis of which, precise control of the servo motor is enabled.

The following glossary entry covers:

Definition and terms used

The resolver determines the angular position and speed of a motor connected to it via electro magnetism. The electromagnetically measured singles are converted and are forwarded to the control elements as actual values. By the comparison with the set value, any discrepancies are detected and adjusted immediately.

How it works

Basic form:
Within the component, a rotor winding and two stator windings are positioned opposite each other. The stators are arranged at a 90°-angle to each other. Based on the current flow induced between the rotor and stators with an applied alternating voltage, the resolver can generate a signal that represents the angular position in a specific moment. This information can be converted and forwarded to connected measuring instruments – particularly a servo-controller – which enables the control of the angular position and the speed of the motor.

As the basic principle is based on the ratio of the rotor to two reference points arranged at right-angles, it can also be modified. For example, two rotor windings can be used in conjunction with one stator reference point, as well as four-pole angular position encoder.

Electric motor with resolver


Particularly in conjunction with the servo-controller, the resolver is of significant importance for the electric motor. It generates the signal with which the precise control of rotor positions is made at all possible. In simplified terms, it can therefore be stated that the resolver generates the data basis, on which the position of the servomotor can be determined. This works because the resolver is connected to the rotational axis, i.e. the shaft of the motor. The rotor turns similar to the rotation of the motor, while the stators are fixed in the surrounding housing and provide a fixed reference variable.


Permanent communication takes place between the resolver and the controller. Due to the resolver, the servo-controller” knows in which position the rotor is and the speed in every millisecond. The servo-controller is thus given the opportunity to actuate the servomotor precisely. This is particularly important in numerous industrial production processes, in which dynamic changes in speed and positions are required.

Resolvers compared to other angle transmitters

The resolver is a special type of angle transmitter. It is relatively simple and therefore particularly robustly built, for example, to withstand lateral acceleration, impacts and large vibrations. The purely electromechanical components are also resistant to chemicals, oil, temperature fluctuations and many other influences.

Use in conjunction with Baumüller drives

In the specific application, the resolver is a signal converter that is used, for example, with the servo-controllers of Baumüller's b maXX series. We offer individual, flexible drive solutions from a single source. The resolver provides the basis for the data synchronization between the servomotor, servo-controller and our parameterization and diagnostics tool ProDrive. In the ProDrive, for example, an integrated real time oscilloscope, an FFT analysis, an encoder diagnosis and other diagnostic functions are available to the user. They can therefore analyze and control highly dynamic processes, precisely and reliably, in all kinds of different industrial applications.


The resolver is a key component in the control of servomotors. The measuring instrument measures voltages inside it and assigns angular positions to them. The connection with the motor shaft allows the resolver to precisely actuate angular positions and control of the speed. To this end, the signals are converted and are forwarded to the servo-controller, in order to ensure continuous monitoring of the relationship between set and actual values.

Do you have any questions?

Matthias Beetz
Training Engineer Academy I Baumüller Nürnberg GmbH

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