The MSR 40 is a modular steel tape rotary encoder from RSF Elektronik that measures applications with diameters of six inches (150 mm) to six feet (about 2 m). Available in North America through Heidenhain Corporation, applications for this ring encoder include rotary tables, telescopes and medical instrumentation.

The steel tape of the MSR 40 uses the single-field scanning principle with 200 μm grating pitch and high achievable angular resolution for simpler mounting. The system has ±30 μm/m accuracy with operating temperature 0 degrees Celsius to +50 degrees Celsius. The encoder operates at high speeds, especially in large measurement applications.

The MSR 40 encoder links the ends of steel tape together with one or two joining mechanisms, depending on the application. Measurement through a full 360 degrees is possible. An MOR version uses a steel ring tensioning cleat for encoders mounted to a steel surface, which allows for thermal expansion. An MER version uses a rubber gasket with a low-profile tensioning cleat for other mounting surfaces.

Depending on the shaft diameter, up to 20,000 line counts are available on the MSR 40. Each version offers quasi-absolute positioning via distance-coded reference marks or homing via a single reference mark. The encoder is available in standard and custom sizes.