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• Observes the mechanical motion of the actuator shaft—a change of position and the rate of change.
• Converts the mechanical input into an electrical impulse and transmits a series of such impulses as a quadrature signal to a controller.

To obtain velocity or angular displacement data, an encoder in a servo motor can be replaced with a potentiometer, a resolver, or a Hall effect transducer. However, the alternatives demonstrate inferior robustness, responsiveness, and reliability in most cases.

Advice on selection

Choosing a sensor to match a servomechanism requires exploring the specifics of the system where the assembly is supposed to be integrated, in particular:

• Type of propulsion. An application, where movements are along a straight-line trajectory, demands a linear detector. In machines performing angular displacements, the preferred type is rotary.

• Mounting method. The encoder body can incorporate a shaft, in which case it is assembled with the drive unit by means of a coupling. While enabling proper alignment, the coupling also isolates the sensing element from a drive unit, both mechanically and electrically.

An alternative is a hollow-shaft mounting arrangement, using a springed tether. The method eliminates the need for alignment and associated failures, but demands special measures to be taken to ensure electrical isolation from the drive unit. A third option is bearingless mount composed of a sensing element installed on the engine face and a magnetic element—on the shaft