Open Optical Encoder:

How it works: An optical sensor reads the coded information on the steel tape ruler. A grating scale or optical marker is on a steel strip ruler, and the sensor measures the position by detecting changes in these optical patterns.
Advantages: Provides high resolution, high measurement accuracy. Since there is no closed housing, it is generally easier to integrate into various systems.
Disadvantages: It is more sensitive to pollution and vibration in the environment, because its working principle requires optical sensors to accurately read the optical scale.

Closed Linear Scale:

How it works: On the glass ruler of the measuring system, there is usually a closed housing to protect the ruler from dust, moisture and other contaminants in the environment. The sensor inside reads the coded information on the glass ruler through the window of the enclosed housing.
Advantages: Compared with open optical encoders, closed grating ruler is more resistant to interference from environmental conditions and less sensitive to pollution and vibration.
Disadvantages: In general, the resolution of the closed grating ruler may be lower than that of the open grating reading head, because the closed structure may limit the fine reading of the sensor.
The choice of which type of measuring equipment to use usually depends on the specific application scenario and requirements. Open optical encoders may be selected if the environment is relatively clean and the accuracy requirements are high. If the working environment is harsh and stronger anti-interference performance is required, then the enclosed linear ruler may be a better choice.