String Potentiometers Information

Image Credits: BEI Sensors, Fraba, and RDP Electrosense

String potentiometers precisely measure linear position. They are also known as cable extension transducers, cable extension linear position sensors, draw wire sensors, draw wire transducers, yo-yo pots, linear position string pots, and string encoders.

How String Potentiometers Work

These sensors detect and measure position and velocity using a flexible cable, a spring-loaded spool, and a rotational sensor. With the body fixed to a surface and the stainless steel cable attached to a movable object, the device produces an electrical signal that is proportional to the cable's extension or velocity. This signal can be sent to a display, a PLC, or data acquisition system.

Types of String Potentiometers

Two sensor types can be found in these devices: a potentiometer or an optical or magnetic encoder.

Specifications and Features

Measurement ranges vary (e.g., 25 to 600 inches).

Measurement reporting varies in accuracy (e.g., within 15% to within 1%).

Position and/or velocity can be measured.

Electrical output signals can be analog (current, voltage, or frequency), digital (serial, parallel, or other), an alarm, or a change in state of switches.

Sensors can be more or less packaged. A sensor element has no packaging. A transducer is housed and may have powered signal conditioning. Instruments or meters are self-contained and display output at or near the device. A gauge or indicator has an analog display and no electronic output.

Devices can tolerate maximum shocks, maximum vibrations, and certain temperature ranges (e.g., 15 to 158 F).

Applications

String potentiometers are used in applications as diverse as bone densitometers in the medical industry, crash testing in the automobile industry, pump jacks in the crude oil extraction industry, and irrigation and flood control in the water management industry. They are also used in cutting concrete, controlling hydraulic cylinders, and grinding metal. Because the cables are flexible metal and often coated, these devices are ideal for wet, dirty or outdoor environments and when the measuring range is awkwardly positioned.

References

Cable Extension Transducer

Cable Extension Transducer, Principles of Operation

Linear Position Transducers