The blue trace clearly shows how the sin/cos amplitude drops off far more abruptly for our standard 12mm disk; model R1206. At +/-200µm, the signal amplitude has dropped to only 20% of the ideal. In order to maintain suitable signal strength for accurate interpolation, the acceptable misalignment should be limited to +/-100µm or less.
When designing a mounting scheme for a MicroE encoder system, particularly one with a small diameter rotary scale, it is important to provide adequate adjustability to the encoder sensor head mount. This will enable fine adjustment to the sensor/scale orientation to compensate for inevitable tolerance stack-up issues. Relying on benching surfaces for small diameter rotary scales is not recommended.
Please contact Celera Motion Applications Engineering group with any questions regarding these recommendations.