Product Datasheets

FAQ | What's A String Pot?

Cable Extension Transducers, Principles of Operation


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

Simply mount the transducer's body to a fixed surface and attach the stainless steel cable to the movable object. As the object moves, the transducer produces an electrical signal that is proportaional to the cable's linear extension or velocity. This signal can then be sent to a display, a PLC or data aquisition system

How Do They Work?

Cable-Exension Tranducers (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 unreels.

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 movalble object, it causes the spool an sensor shafts to rotate. The rotating shaft creates an electrical signal proportional to the cable's linear extension or velocity.

What Kind of Output Signals Can I Have?

Celesco offers all industry-standard output signals, these include:

What Advantages Do CET's Have?

Measuring the movement and position of objects is easy with CETs.

CETs can be installed in minutes, fitted into prcarous 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.

CETs 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?

Celesco 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.