A string encoder (also called a cable encoder or draw-wire encoder) is a type of position sensor that measures the movement of an object using a retractable cable or string. These encoders are primarily designed for measuring linear displacement or distance and are appreciated for their mechanical simplicity and ease of installation.

The working principle of a string encoder is quite straightforward: a cable or string is wound around a spring-loaded drum. When the target object moves, the string is either pulled out or retracted onto the drum. The rotation of this drum is captured by a rotary encoder, which then converts the angular displacement into an electrical signal proportional to the object’s linear position.

This conversion allows the encoder to accurately track linear motion using a compact mechanical system. Depending on the internal encoder type (either incremental or absolute), it can provide pulse-based feedback or absolute position data, making it suitable for various measurement and control tasks.

String encoders are widely used in machine control, industrial automation, lifting and handling systems, construction machinery, and vehicle positioning applications. Their biggest advantages include long measurement range, durability, and compact design, allowing precise measurement even in limited spaces where optical or laser sensors cannot be easily mounted.

From a practical standpoint, string encoders provide a reliable way to measure long-distance linear travel — often from a few centimeters up to several meters — without complex installation. They are especially valued in environments where mechanical feedback and real-time position monitoring are required.

However, due to their mechanical nature, the cable and drum mechanism are subject to wear and tear over time. Regular inspection and maintenance (e.g., cleaning and ensuring proper spring tension) are important to maintain measurement accuracy and extend service life.

In summary, a string encoder combines the precision of rotary measurement with the convenience of linear feedback. Its simple yet effective design makes it one of the most versatile and cost-effective solutions for linear position measurement in industrial environments.