string pot

TE CONNECTIVITY (TE) String Potentiometers

A string potentiometer, sometimes also known as a string pot, a draw wire senor, a string encoder or a yo yo pot, is a cable actuated position sensor used to detect and measure linear position and velocity using a flexible cable and a spring-loaded spool.

In order to take measurements, the transducer's body is mounted to a fixed surface and the stainless steel cable is attached to the movable object. As the object moves, the transducer produces an electrical signal that is proportional to the cable's linear extension or velocity. This signal can then be sent to a display, a PLC or data acquisition system.

How do they work?

String pots or cable-extension transducers (CETs) are composed of four main parts:

  1. Measuring Cable
  2. Spool
  3. Spring
  4. Rotational Sensor

Inside the transducer's housing, a stainless steel cable is wound on a precisely machined constant diameter cylindrical spool that turns as the measuring cable reels and un-reels.

string pot position sensor

To maintain cable tension, a spring is coupled to the spool. The spool is coupled to the shaft of a rotational sensor (an encoder or potentiometer). As the transducer's cable extends along with the movable object, it causes the spool and sensor shafts to rotate. The rotating shaft creates an electrical signal proportional to the cable's linear extension or velocity.

What type of output signals are available?

  • Potentiometric (Voltage Divider)
  • 0...10 Volts DC
  • 4...20 mA (2-wire)
  • 0...20 mA (3-wire)
  • Incremental Encoder (Quadrature)
  • Absolute Encoder (ask factory)
  • RS232/RS422 Communications
  • DeviceNET®
  • CANbus J1939
cable actuated position sensor
PT8000 cable actuated position sensor

What advantages do string pots have?

Measuring the movement and position of objects is easy with string pots. String potentiometers can be installed in minutes, fitted into precarious or tight areas and they do not require perfectly parallel alignment. They also offer great flexibility, a small size to measurement ratio and they cost less than rod or wand-type measurement devices. String pots can be used in a wide variety of applications including industrial factory automation, high-tech medical devices, structural and automotive testing, die-casting or injection molding, hydraulic cylinder control or just about anything else you can think of.

What measurement ranges are available?

TE currently offers full stroke ranges from as small as 0-2 inches and all the way up to 0-1700 inches (140 ft). If you've got any questions or need help selecting a specific model, please don't hesitate to give us a call and one of our applications engineers would be glad to help.