Technical Blog

Draw Wire Sensors

Draw Wire Sensors is another term used for cable extension transducers, they are also known as string pots, yo yo pots and cable-actuated position sensors.

Draw wire sensors are a type of linear position sensor. They use a cable and a spring-loaded spool to measure and detect linear displacement.

Draw Wire Sensor Operating Principle

Draw wire sensors are small in size compared to their measuring range. Often a draw wire sensor would be selected for an application if space were limited or if the measuring range was very large.

Draw wire sensors consist of a flexible measuring cable, a spool, a spring and a rotational sensor (typically a potentiometer).

The measuring cable is precisely wound around the spool; the rotational sensor is also attached to the spool. One end of the cable is attached to the object requiring measurement. As the cable is pulled it unravels from the spool which turns the rotational sensor allowing it to accurately measure the distance the object has moved based on the number of rotations it has taken. The spring is required to maintain tension within the mechanism.

Advantages of Draw Wire Sensors

Draw wire sensors have a great size to measurement ratio. A small device can measure a very long distance making them well suited for applications where large measurement ranges are required. Other advantages include;

  • Easy to use
  • Fast installation
  • Great flexibility
  • Good value for money
  • Diverse
  • Do not require perfect parallel alignment

Draw Wire Sensors from Variohm

Our draw wire sensors come from our supplier TE. They are available with various outputs, these include;

  • Potentiometric (Voltage Divider)
  • 0...10 Volts DC
  • 4...20 mA (2-wire)
  • 0...20 mA (3-wire)
  • Incremental Encoder (Quadrature)
  • RS232/RS422 Communications
  • DeviceNET®
  • CANopen
  • CANbus J1939

Full stroke ranges of our draw wire sensors are from 0-2 inches to 0-1700 inches. Other features and benefits of the TE range of draw wire sensors include;

  • In stock packages for fast delivery as well as custom designs available.
  • Industrial line with measurement ranges up to 43 meters – suitable for either indoor or outdoor use.
  • Various outputs.
  • Variety of different housings for different ranges making them suitable for various environments.
  • Open frame designs suitable for OEMs.
  • High accuracy and repeatability.
  • Protection rated to IP68.
  • High maximum operating temperature (121°C/ 255°F).

For more information on our selection of draw wire sensors or to discuss your application please contact us.

Article published on: 03/07/2020