Draw Wire Encoders vs String Potentiometers

String potentiometer or draw wire encoder
11 May 2020

When selecting a linear displacement sensor, you often find two different technologies are under consideration: 

  • String Potentiometers (string pots) 

  • Draw Wire Encoders 

The mechanical design principles of both are similar, with the main deciding factors being travel length and robustness. 

However, when it comes to the electronics there are many different options to choose from. 

As well as a broad variety of rotary encoders being available, you also have what is essentially a multiturn potentiometer with some additional signal conditioning electronics. 

There are some fundamental differences between Draw Wire Encoders and String Potentiometers and the technology selected will very much depend on the linear displacement application at hand. 

It should be said that the term “string pot” seems somewhat disingenuous when all models supplied by ADM Instrument Engineering are fitted with high quality wire rope.  

String Pot Features 

UniMeasure LX Series String Potentiometer

  • lndustry standard analogue output signals such as 4-20mA, 0-10V, resistance or radiometric. 

  • Simple set up with Zero and Span user adjustments 

  • Easy to fault find. 

  • Suitable for shorter travel lengths; down to 38mm 

  • Also suitable for longer travel lengths; up to 50m 

  • Accuracy is comparable with most encoders 

Draw Wire Encoders  

POSITAL LD0-D2C1B-1212-5G90-5RW Draw Wire Encoder

A wide variety of absolute encoders are available with industry standard communication protocols such as Ethernet and Serial Fieldbus. 

There are also models available with analogue electrical outputs for direct connection to a wider range a controllers and PLCs. 

Fieldbus communications allow for multi-dropping many sensors with only one cable run. 

Mechanical Advantages of Draw Wire Transducers and String Potentiometers 

Linear displacement measurement sensors and transducers all have moving parts and are often used in the harshest of environments.  

Therefore, reliability is crucial, which is why ADM Instrument Engineering has chosen to represent reputable manufacturers such as UniMeasure, a United States based manufacturer of string pots and POSITAL a, German manufacture of draw wire encoders. 

Both types of linear displacement sensor have the advantage that they do not need to be mounted directly in line with the moving target. This means they can be mounted away from “the action” where they are not so exposed to dust and moisture.  

IP rated models are available for use in dusty, or damp environments. 

For further information please contact ADM Instrument Engineering on 1300 236 467 to speak to one of our engineers in your area.