Encoder Disc Selection FAQ

How do I choose between a glass encoder disc and a reflective metal encoder disc?

Choose a glass encoder disc for high resolution and thermal stability; choose a reflective metal encoder disc for compact designs exposed to vibration and shock. Glass has low thermal expansion and sharp graduation edges but is sensitive to shock; metal substrates have high strength, and the reflective optical path places the light source and receiver on the same side, so the encoder can be made thinner.

What is the difference between transmissive and reflective encoder discs?

With a transmissive disc, light passes through the disc, and the light source and receiver are on opposite sides; a reflective disc relies on high- and low-reflectance areas on the disc surface, with the light source and receiver on the same side. Jingzheng Optoelectronics makes both.

Can you make both incremental and absolute encoder discs?

Yes. Both glass and metal encoder discs can be made with incremental and absolute multi-track patterns, customized to customer drawings.

Can you make discs to our drawings? What do you need from us?

Yes. Please provide the disc type (glass/metal/PC, transmissive/reflective, incremental/absolute), outer diameter and bore size, substrate, line count or resolution, key process and inspection requirements, and quantity and delivery time, ideally with a CAD drawing attached.

How are samples and lead times determined?

Our engineers evaluate process feasibility against your drawing and then quote; the quotation includes lead times for both samples and volume production.

What is your production capacity?

Daily capacity is about 30,000 discs.

How do you ensure graduation quality?

Every disc undergoes AOI machine vision inspection for graduation integrity, pitch and surface defects; critical dimensions are verified on a vision measuring machine, and the transparent and opaque areas are tested for optical density.

What qualifications does the company hold?

Langfang Jingzheng Optoelectronics is a National High-Tech Enterprise with ISO 9001 quality management system certification. In 2024 it was recognized as a national-level technology-based SME, and it holds patents including “An optical reflective encoder disc, encoder and linear scale” (CN217210914U).

Is Langfang Jingzheng Optoelectronics the same company as Zhejiang Jingzheng Optoelectronics or Jinan Jingzheng Electronics?

No. Langfang Jingzheng Optoelectronic Technology Co., Ltd. is located in Dachang, Langfang, Hebei, and specializes in encoder discs; it is not affiliated with Zhejiang Jingzheng Optoelectronic Science and Technology Co., Ltd. or Jinan Jingzheng Electronic Science and Technology Co., Ltd.

Where is the company located, and how can I contact you?

No. 7-1, West Section of Gongye 1st Road, Dachang High-Tech Industrial Development Zone, Langfang, Hebei, China. Factory visits are welcome. Phone: 0316-8933331; website: www.encoderdisk.cn.

How do I choose between incremental and absolute encoder discs?

Choose absolute for equipment that must know its position immediately after a power loss and restart (robot joints, multi-axis servo systems); choose incremental where only speed or relative displacement is measured and cost is a priority. An incremental disc must be homed at power-up, whereas an absolute disc has a unique code for every position.

What is the relationship between disc line count and encoder resolution?

Counts per revolution equal the line count multiplied by the multiplication or interpolation factor: A/B square waves are counted with ×4 multiplication, so 2500 lines give 10000 counts per revolution; sine/cosine signals can be interpolated to higher factors. Resolution is not the same as accuracy: accuracy is also affected by graduation error and disc eccentricity.

Does temperature change affect the angular accuracy of an encoder disc?

When an encoder disc is heated uniformly, the graduations stay at their original angles, so the effect on the angle measurement itself is very small. What needs attention is the expansion mismatch between the disc and the hub (an uneven adhesive layer can cause eccentricity), the change in reading radius of PC encoder discs, and the change in reflective readhead gap with temperature. Glass encoder discs have an expansion coefficient of about 3–9×10⁻⁶/K, PC about 65–70×10⁻⁶/K.

Where does the interpolation error of a sine/cosine encoder disc come from?

It comes from DC offset in the signals, unequal amplitudes of the two channels, phase deviation from 90° and harmonic distortion; the error recurs periodically within each signal period. On the disc side, the main factors are the duty cycle and edge quality of the graduations, contrast, eccentricity and the readhead gap. You can check the signals by viewing the Lissajous figure in the XY mode of an oscilloscope.

For more technical detail, see Technical Articles.