What is a String Pot?

What is a String Pot?

A String Pot is short for String Potentiometer which is an alternative name for a Cable Extension Transducer. Other names for string pots are; draw-wire sensor, yo-yo pot, string encoder and cable-actuated position sensor. 

A string pot is a type of linear position sensor, they detect linear position and velocity using a flexible cable (string) and a spring-loaded spool. 

How does a string pot work

String pots consist of a measuring cable, a spool, a spring and a rotational sensor. The cable is wound tightly around the spool, the diameter of the spool is constant. The spring is in place to maintain the tension & retraction of the cable. 

The end of the cable is attached to the moving object, as the object moves the cable un-reels and reels. The rotating spool drives the shaft of the sensing device creating electrical signals proportional to the linear extension and velocity of the cable. 

What is a string pot used for?

String pots are so versatile they can be used for a wide range of applications. They are often selected for applications where space is limited as they have a better stroke to length ratio than a linear transducer. Some application examples are; 

• Factory automation
• Mobile vehicle
• Medical devices and machines 
• Structural testing 
• Automotive testing 
• Telescopic applications
• Hydraulic cylinder control 

Advantages of using String Pots

Sometimes string pots are selected for use for one or more of the following advantages; 

• Fast installation - can be installed in minutes
• Can fit into small spaces - suitable for applications with limited space
• Do not require perfect parallel alignment to function accurately 
• Small size to measurement ratio
• Good value for money and lower cost than other linear alternatives 
• Suitable for a wide range of applications 

String Pots from Variohm 

Our string pots come from our supplier TE. We have been supplying these string pots for many years. The full range can be seen on our website. 

The full stroke ranges of our string pots range from 0-2 inches up to 0-1700 inches (140ft)

We can offer the following outputs;

• Potentiometric (voltage divider)
• 0...10 Volts DC
• 4… 20 mA (2-wire)
• 0… 20 mA (3-wire)
• Incremental Encoder (Quadrature)
• Absolute Encoder
• RS232/ RS422 Communications 
• DeviceNET
• CANbus J1939

Individual datasheets provide full details on outputs, stroke ranges and other specifications so take a look at the product pages for more information;

SP Series - small in size, stroke to 1370mm, polycarbonate enclosure

SE1 Series - digital encoder, small in size 

SM Series - ultra-compact design, stroke range to 25 inches 

SG Series - IP67, extremely durable 

SR Series - suitable for outdoor applications, rugged, IP67

SK Series - rugged, IP67

Miniature Series - well suited for Motorsport

PT1 Series - slow to moderate acceleration applications

Classic Series - suitable for laboratory, non-hostile environments 

PT5 Series - high acceleration and high cycle applications, IP67, NEMA 6

PT8 Series - Hazardous Area certified, industrial environments 

PT9 Series - Hazardous Area, long-range demanding applications 

PT9 EXT Series - extended series, long-range applications