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).
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.
Related Products & Services
Capacitive Linear Position Sensors
Capacitive linear position sensors are devices that sense position / displacement using capacitance technology.
Eddy Current Linear Encoders
Eddy current linear encoders detect the distance from a target by using magnetic fields generated by a reference and sensing coils.
Linear Variable Differential Transformers (LVDT)
Linear variable differential transformer (LVDT) linear position sensors have a series of inductors in a hollow cylindrical shaft and a solid cylindrical core. These devices produce an electrical output proportional to the position of the core
Optical Linear Encoders
Optical linear encoders use fiber optic technology to sense position and displacement.
Optical Triangulation Position Sensors
Optical triangulation position sensors use reflected waves to pinpoint position and displacement. The source of these waves may be a light emitting diode (LED), infrared (IR) light, or laser.
Photoelectric sensors use emitters and receivers to detect the presence, absence, or distance of target objects.
Ultrasonic Linear Position Sensors and Switches
Ultrasonic linear position sensors and switches use ultrasonic waves in combination with light and frequency readings for position and displacement sensing.