Potentiometric Sensor Design

Friday, November 17th, 2017 - Passive Transducers, Resistive Transducers

Potentiometric Sensor Design

Potentiometric sensors are available in two configurations: linear and rotary, as shown in Figure 1.a and b, respectively. In both configurations, resistance change is the result of position variation (x or θ) of a movable contact (wiper) on a fixed resistor, resulting in an output voltage change.

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Figure 1. Linear (a) and rotary (b) potentiometer configurations.

Linear Potentiometers

Major components of a linear potentiometer include three terminals (power input, ground, and sensor signal output), a fixed resistor, a wiper, a sliding track, and the housing. The terminals are often gold plated to prevent corrosion or tarnishing. The resistor is usually made of high-quality conductive materials (e.g., copper) with a lower temperature coefficient for stability and long life. The wiper uses high-quality metal or alloy (e.g., a platinum alloy) for long life and low noise. Some wipers even have a multifinger shape to prevent intermittence when used in high shock or vibration environments.

The wiper is connected to the moving object being measured through threads, chamfers, or spring returns. Some potentiometric sensors have other components, such as guide rails (to enhance stability during wiper sliding) and wave washers for antibacklash control. The housing holds the components in place and protects the sensor from harsh environments.

The major considerations in a linear potentiometric sensor design include

  • The length of the stroke to be measured
  • Power rating and resistance value
  • The space limitations
  • The quality of the conductive element
  • The means of connecting the sensor to the moving device being measured

Rotary Potentiometers

There are two different designs of rotary potentiometers: single-turn and multiturn. A single-turn potentiometer rotates less than one full revolution (i.e., <360°) to reach its full resistance range. It is often used as an angular position sensor. A multiturn potentiometer rotates more than one revolution (e.g., 5, 10, 20, or 25 turns) to reach its full resistance range, and it is often used where a higher resolution adjustment or multiple revolutions are required. Multiturn potentiometers are more expensive, but very stable with high precision. Similar to linear potentiometers, both single-turn and multiturn potentiometers have three terminals, a fixed resistor, a rotary wiper, a shaft, and the housing. The wire-wound resistor in a rotary pot often uses a material that has a lower temperature coefficient to improve the stability. A conductive plastic is sometimes molded over the wire-wound resistor to reduce inductance and protect the resistor.

The major considerations in a single-turn or multiturn rotary potentiometer design are

  • Angle or rotation to be measured
  • Power rating and resistance value
  • Resolution. Choose a single-turn design if resolutions above 10% are acceptable (less expensive). Choose a multiturn design if higher resolution is required (e.g., 1%—finer control, better linearity and stability)

I hope this information about “Potentiometric Sensor Design” is useful.