Mounting Tolerance – Netzer vs Optical Why Mounting Tolerance Matters: Capacitive vs. Optical Encoders Introduction In practical motion systems, perfect alignment is rare rather than typical. Minor mechanical deviations—such as eccentricity, axial displacement, or tilt—can lead to meaningful angular errors. The real question isn’t whether misalignment will occur, but how sensitive the encoder is to those imperfections. The comparison below illustrates the core differences between optical and capacitive encoders when operating under real-world conditions. Measured Sensitivity to Tilt – Netzer’s capacitive vs Optical (both 100 mm encoders) Measured Sensitivity to Tilt – Netzer’s capacitive vs Optical (both 100 mm encoders) Optical encoders generate ~114 mdeg error per 0.1 mm eccentricity, while Netzer capacitive encoders maintain ~1.5 mdeg — delivering ~75× lower sensitivity. The Hidden Challenge in Encoder Integration When selecting an encoder, engineers often focus on resolution, accuracy, and interface protocols. However, one of the most critical factors, and often underestimated, is mounting tolerance. In real-world systems, perfect mechanical alignment is rarely achievable. Radial offset, axial displacement, shaft tilt, eccentricity (runout), and thermal expansion all introduce misalignment. The ability of an encoder to maintain signal integrity and accuracy under these conditions can make the difference between a robust system and a fragile one. Optical Encoders: High Precision, Low Tolerance Optical encoders rely on light passing through or reflecting off a finely patterned code disk. This method enables very high resolution, but it depends on a precise optical path between emitter, code disk, and receiver. Sensitivity to Misalignment Because the sensing is localized and optical-path dependent, optical encoders are inherently sensitive to: Radial misalignment (shaft-to-sensor offset) Axial displacement (gap variation) Angular misalignment (tilt) Eccentricity / dynamic runout These deviations introduce: Signal distortion Phase error between channels Interpolation degradation Potential loss of signal under extreme conditions Practical Implications Tight mechanical tolerances (µm-level in many cases) Precision alignment fixtures required Increased sensitivity to vibration and thermal drift Vulnerability to contamination (dust, oil, condensation) In practice, this results in higher integration effort, increased system cost, and reduced robustness in non-ideal environments. Capacitive Encoders: Designed for Real-World Conditions Netzer’s capacitive encoders operate on a fundamentally different principle. Instead of relying on light, they measure variations in an electric field between rotor and stator electrodes. Why Capacitive Sensing Is More Tolerant Unlike optical systems, capacitive sensing is distributed over the sensing geometry rather than dependent on a single optical path. This creates an inherent averaging effect, making the system significantly less sensitive to local geometric deviations. As a result, capacitive encoders maintain stable signal quality even under: Radial offset Axial gap variation Shaft tilt Dynamic runout and vibration Typical Tolerance Comparison (values depend on model) Parameter Definition Capacitive Encoder (Netzer) Optical Encoder (Typical) Radial misalignment Static offset between shaft and encoder center up to ~0.1 mm ~0.01–0.02 mm Axial displacement Change in gap along shaft axis up to ~0.1 mm ~0.01–0.02 mm Tilt (angular misalignment) Angular deviation between shaft and encoder axis Tolerant, minimal signal impact Very limited (<0.05°) Eccentricity (runout) Dynamic offset during rotation (wobble) up to ~0.1 mm ~0.01–0.02 mm Values are indicative and vary by manufacturer and resolution class. High-resolution optical encoders typically require tighter tolerances. Engineering Takeaway Capacitive encoders provide ~5–10× higher mechanical tolerance and up to ~75× lower sensitivity to eccentricity-induced error compared to typical optical encoders. Real-World Impact: From Design to Deployment 1 – Simplified Mechanical Design Reduced machining precision requirements Less complex mechanical interfaces Greater flexibility in shaft and housing design 2- Faster Integration and Assembly Reduced alignment effort during installation Lower dependency on precision fixtures and shimming Faster time-to-production 3- Improved System Robustness Under real operating conditions (vibration, thermal drift, wear): Capacitive encoders maintain stable amplitude and phase signals Optical systems are more prone to signal degradation over time 4- Lower Total System Cost Reduced mechanical cost (tolerances, machining) Lower assembly time Fewer field failures and maintenance events Conclusion Optical encoders deliver excellent performance in tightly controlled, precision-aligned systems. However, their reliance on a precise optical path makes them inherently sensitive to real-world mechanical deviations. Capacitive encoders, by contrast, are designed for tolerance. By maintaining performance under radial, axial, and angular misalignment, they enable: Easier integration Lower system cost Higher long-term reliability For engineering teams designing systems that must perform outside of ideal lab conditions, capacitive technology provides a clear, measurable, and practical advantage.
