Technical Articles
Practical information on encoder disc selection, processes and inspection.
- Encoder disc glossary: 30 common terms explained
Common encoder disc and optical encoder terms with concise definitions: incremental, absolute, transmissive, reflective, track, line count, grating pitch, duty cycle, interpolation, Gray code, eccentricity, optical density, reflectance and more. - Does temperature change affect encoder disc accuracy? How to evaluate substrate thermal expansion
Uniform thermal expansion does not change the angular positions of the graduations, so its effect on the angle measurement itself is very small; what really matters is the expansion mismatch between the disc and the hub, the change in grating pitch at the reading radius, and the gap of reflective readheads. This article gives expansion coefficients for common substrates and worked examples. - Where does the interpolation error of sine/cosine encoder discs come from? 4 signal quality metrics to check
DC offset, amplitude mismatch, phase deviation from 90° and harmonic distortion in sine/cosine signals produce a periodic interpolation error within each signal period. This article shows how to estimate each term, the factors on the disc side, and how to check the signals with a Lissajous figure. - What is the difference between incremental and absolute encoder discs? How to choose
An incremental encoder disc outputs pulses and must be homed after power-up; an absolute encoder disc has a unique code for every angle, so the position is known at power-up. This article compares the two in terms of tracks, resolution, signals and cost, and gives selection advice. - How do you choose the line count of an encoder disc? Line count, interpolation and encoder resolution
Encoder resolution equals the disc line count multiplied by the multiplication or interpolation factor. This article gives the conversion formulas and common combinations, explains the relationship between grating pitch and reading radius and the difference between resolution and accuracy, and sets out the steps for working back from requirements to a line count. - What should incoming inspection of encoder discs check? Visual defects, dimensions and optical parameters
A checklist for incoming inspection of encoder discs: visual defects, dimensions and concentricity, graduation quality and optical parameters, plus the inspection methods, sampling and acceptance criteria to agree with the supplier in advance. - Reflective metal or glass encoder disc? Choosing by optical path, accuracy and environment
For high resolution and long-term accuracy, choose a glass encoder disc; for a thin, vibration- and shock-resistant, cost-controlled encoder, choose a reflective metal encoder disc. This article compares the two disc types in terms of optical path, accuracy and thermal stability, and mechanical environment. - Weak signal and large interpolation error with a reflective disc? Check the high/low reflectance contrast first
The signal of a reflective encoder comes from the difference in light intensity between the high- and low-reflectance areas of the disc. This article gives the contrast formula with examples, explains why lowering the low reflectance is more effective than raising the high reflectance, and lists the optical parameters to state clearly in an RFQ. - How much angular error does 5 μm of disc eccentricity cause? Sources, measurement and control of eccentricity
In a single-readhead encoder, disc eccentricity e produces a once-per-revolution sinusoidal angular error with an amplitude of about e divided by the reading radius r. This article gives worked examples and explains where eccentricity comes from, how to measure it, and how to control it in manufacturing and assembly. - Requesting a quote for a custom encoder disc: 20 parameters to send the manufacturer
A checklist of the 20 parameters to provide when requesting a quote for a custom encoder disc: type, dimensions, tracks, accuracy, optics, process, environment, quantity and delivery, with example entries.