A multiturn rotary encoder is a sensor that measures the angle of rotation of a shaft, as well as the number of complete revolutions that the shaft has made. This is in contrast to a single-turn encoder, which only measures the angle of rotation, 0 – 360°. Multiturn encoders are used in a variety of applications where it is important to track the position of a moving object, such as in machine tools, robotics, and automation systems.

Recently, obtaining the Inductosyn and components for maintenance has become more difficult. For decades the Inductosyn from Farrand Controls / Ruhle Companies sat near the top of the rotary sensor hierarchy. Providing sub 2 arcsec (0.5 mdeg) accuracies, it combined the robustness of a resolver with the performance of the best optical encoders. Despite its shortcomings, it found plenty of customers, from airborne infrared and radar systems, to telescopes, satellite communication antennae (SATCOM), machine tooling and low-pressure vacuum chambers.

There are several key terms that are critical to specifying the optimal position sensor for a given application. This application note defines these key terms and how they relate to the sensor’s role in the overall system performance. It is important to consider that precision is very much a system issue and can be dominated by mechanical errors such as eccentricity. This paper discusses the most significant mechanical error for rotary applications (eccentricity) and presents eccentricity tolerant position sensor solutions.