Linear Potentiometers: Types, Specs & How to Choose

Most component searches end at a datasheet. This one usually doesn’t, because “linear potentiometer” covers at least five meaningfully different devices — a 0.5 mm adhesive-backed membrane strip and a stainless-shafted industrial transducer are both sold under the name, and they fail in completely different ways.

This guide is for engineers specifying a part rather than learning the theory: what a linear potentiometer is, the types available, the specs that actually decide between them, and a selection path that gets you to a part number. For fundamentals, start with What Does a Potentiometer Do? and Variable Resistors Explained.

What Is a Linear Potentiometer?

A linear potentiometer reports absolute linear displacement as a resistance — and, wired as a voltage divider, as a proportional voltage. Three terminals: both ends of a resistive track, plus a wiper contacting it somewhere along its length. Apply a reference voltage across the ends and the wiper outputs a fraction of it corresponding to its position:

V_out = V_in × (position / total travel)

Half travel, half voltage. That’s the whole operating principle, and it’s why these remain the cheapest reliable way to turn linear motion into an analog signal a microcontroller or PLC reads directly — no signal conditioning, no excitation electronics, no protocol.

The property most often overlooked: a potentiometer is inherently absolute. Power it up and it already knows where it is, while an incremental encoder must run a homing routine first. If your machine can lose power mid-cycle and needs its position the moment it returns, that matters more than any accuracy spec on the sheet. See Encoder vs Potentiometer.

What Else It Gets Called

The same device is sold under a scatter of names, which is part of why specifying one is harder than it should be:

One trap worth naming. Panel-mount slide potentiometers often ship with an audio (logarithmic) taper, where half travel is nowhere near half resistance. For position measurement you want a linear taper, every time. Membrane and industrial motion potentiometers are linear-taper by default; audio faders frequently are not. If a datasheet doesn’t state the taper, assume nothing.

How a Linear Potentiometer Works

Three parts do the work. The resistive element — printed polymer on polyester in membrane sensors, conductive plastic in rod-style units, with a nominal end-to-end resistance (10 kΩ is the common standard). The wiper — the contact tapping off voltage at its position; internal and captive in a rod-style unit, but in a membrane sensor a separate component you specify and mount yourself, a detail that catches out more first-time users than any other. The actuator — whatever couples your mechanism to the wiper: a shaft eyelet, spring-loaded plunger, cam, or fingertip.

Electrical Travel vs. Mechanical Travel

Different numbers, and confusing them causes real problems. Electrical travel is the distance over which output changes proportionally with position — your usable measuring range. Mechanical travel is how far the actuator physically moves, including dead zone past the ends of the track.

Specify against electrical travel, with margin at both ends. Running against the electrical limits is the most common cause of non-repeatable end-of-travel readings. If you need 48 mm of measurement, don’t buy a 50 mm part.

The Types of Linear Potentiometer

Spectra Symbol’s line covers five, spanning roughly two orders of magnitude in thickness. They are not interchangeable.

Membrane (SoftPot)

The SoftPot is a sealed membrane strip 0.5 mm thick, with electrical travel from 8 mm to 2000 mm. It mounts flat with adhesive and is actuated by a spring-loaded wiper pressing on the membrane — or by a fingertip, which is why it doubles as a touch input.

Independent linearity ±1% or ±3%, life >1 million actuations, IP65, −40 °C to +50 °C. Actuation force is 0.6–1.5 N at room temperature across a 10 mm active cavity.

Best for: tight form factors, long travel, curved surfaces, disposable and high-volume instrumentation. Nothing else gives you two metres of absolute position measurement in half a millimetre of thickness.

Narrow Membrane (ThinPot)

The ThinPot is a SoftPot narrowed for constrained spaces: about 10 mm wide overall against the SoftPot’s 20.32 mm — half the width, same ultra-thin profile — with the same 8–2000 mm travel, ±1%/±3% linearity and >1 million cycle life. The active track is 3.17 mm across.

It ships with 3M 200MP pressure-sensitive adhesive and carries IP64 — dust-proof and splash-proof, a step below the SoftPot’s IP65.

Best for: the same applications as the SoftPot when panel width, not thickness, is the binding constraint. It’s a medical standard for several multinational device manufacturers.

High-Temperature Membrane (HotPot)

The HotPot trades polyester for a fiberglass substrate, producing a different durability class: >10 million actuations — ten times the SoftPot — over −40 °C to +85 °C, rated IP65, with travel from 10 mm to 1200 mm.

One design warning that isn’t obvious from the temperature range. Actuation force is strongly temperature-dependent. Across a 10 mm active cavity the HotPot needs 0.8–2.0 N at +23 °C, but 3.0–5.0 N at −40 °C — up to four times more. A wiper spring sized at room temperature will under-actuate in the cold and drop out. Size for the coldest condition your product will actually see.

(Actuation force is always quoted against a specific cavity width, so figures aren’t comparable between series unless the cavity matches — ThinPot’s 0.7–1.8 N is measured across 6 mm, not 10 mm.)

Best for: engine bays, sterilization cycles, outdoor equipment, and anywhere cycle count is the deciding spec.

Contactless Magnetic (MagnetoPot)

The MagnetoPot removes mechanical contact entirely. An external magnet — on a piston, float or carriage — couples through the sensor body to internal magnetic actuators. Nothing touches the sensor, so nothing wears at the interface, and the sensor can sit outside a sealed vessel. Travel runs 8 mm to 1200 mm, in orderable lengths from 50 mm to 1000 mm.

The trade-offs are real, and worth sizing before you commit:

• Linearity is ±5% standard (±1% available on request). On a 1000 mm unit, ±5% is ±50 mm.
• Hysteresis is about 3 mm, varying with magnet size, strength and standoff. If your positioning tolerance is tighter than that, this is the wrong part regardless of how appealing “contactless” sounds.
• It cannot be mounted to a ferromagnetic surface — steel captures the field.
• Resolution depends on the external magnet’s strength and distance, not the sensor alone.

Best for: liquid level, hydraulic and pneumatic cylinder position, washdown environments, and anywhere the sensor must be isolated from the medium it measures. It gives full-travel position where a reed switch gives only end-of-stroke. See How Magnetic Position Sensors Work.

Linear Motion Potentiometer (MotionPot)

The MotionPot is the rod-style industrial format: anodized aluminium and Nylon 66 housing, stainless steel AISI 303 shaft, mounting via grooves or brackets. Travel spans 8 mm to 500 mm.

It’s the accuracy leader in the line at ±0.5% independent linearity, with >10 million cycles over −40 °C to +85 °C, rated IP60.

Best for: actuator stroke feedback, valve position, test rigs, damper and suspension travel — where you need a self-contained sensor that bolts between two points and survives hard cycling. Note IP60: debris-resistant, not washdown-rated.

Two Adjacent Types Worth Knowing

String potentiometers (draw-wire sensors) use a cable on a spring-loaded spool turning a rotary sensor. Ranges run from about an inch to over 100 feet, making them the honest answer above roughly two metres — past where any membrane sensor goes. Trade-offs: cable sag degrades accuracy, temperature affects both cable length and resistance, and the spool limits tracking speed. At 300 mm of stroke a string pot is unnecessary complexity; at 10 m nothing else here will do.

Rotary potentiometers measure angular position. Before committing to a linear sensor, check whether your motion is already rotary somewhere — a lever arm, pivot or leadscrew. Measuring the rotation is often cheaper and simpler. Spectra’s membrane sensors are available in rotary configurations up to 353° of active angle.

Type Comparison

The Specifications That Decide It

Six numbers do most of the work, in roughly the order they’ll eliminate options.

1. Mounting envelope. This is the specification that most often kills a part choice, and almost no comparison table leads with it. Stroke is rarely the problem — whether the sensor body fits between your mounting points across the full range of motion usually is. Rod-style sensors have a body considerably longer than their stroke; a 50 mm-stroke unit may retract to only 160–180 mm, and if your mounting points sit 150 mm apart at full compression, that part is out regardless of its linearity. Check retracted and extended length first. Membrane sensors sidestep this entirely — a 0.5 mm adhesive strip has no retracted-versus-extended dimension, so its installed envelope is essentially its active length. In tight geometry that’s often the deciding advantage.

2. Electrical travel. Your usable range, per the distinction above. Specify with margin at both ends.

3. Independent linearity. How far output can deviate from a perfect straight line, as a percentage of full travel. Convert it to millimetres before deciding it’s acceptable — this is where specs get misread:

• ±1% on a 100 mm sensor = ±1 mm
• ±3% on a 1000 mm sensor = ±30 mm
• ±5% on a 1000 mm sensor = ±50 mm

The percentage looks small; the millimetres may not. Across the membrane line the ±1% grade typically carries around a 25% premium over ±3% — cheap insurance if your tolerance is tight, wasted money if it isn’t.

4. Resolution vs. accuracy. Frequently conflated, and not the same thing. Resolution is the smallest change the sensor can distinguish — for an analog membrane potentiometer it’s theoretically infinite, limited in practice by your ADC and the wiper’s contact area. A 10-bit ADC over a 100 mm sensor gives roughly 0.1 mm steps. Accuracy is whether the reported position is correct, governed by linearity, hysteresis and repeatability. A sensor can have effectively infinite resolution and still be ±30 mm out.

5. Mechanical life. Rated in actuations: >1 million for SoftPot, ThinPot and MagnetoPot; >10 million for HotPot and MotionPot. Work out your real cycle count first — a sensor cycling four times a minute across two shifts passes a million actuations in under a year.

6. Temperature range and sealing. −40 to +50 °C for standard membrane parts, −40 to +85 °C for HotPot and MotionPot. The hidden interaction is actuation force, which rises sharply in the cold (see HotPot above) — specify the wiper for your coldest condition. For sealing: IP65 (SoftPot, HotPot) resists dust and water jets; IP64 (ThinPot, MagnetoPot) is dust-proof and splash-proof; IP60 (MotionPot) is debris-resistant with no water rating. For washdown, contactless deserves a look, since it can sit outside the sealed boundary entirely.

And one more: resistance value. Standard is 10 kΩ, rising to 20 kΩ above 300 mm of travel, at ±20% tolerance. That ±20% is why these must be used as ratiometric voltage dividers, not absolute-resistance rheostats — in a divider the tolerance cancels, since output is a ratio of input; measure absolute resistance instead and the 20% lands directly in your reading. Higher resistance also means higher source impedance, so more noise susceptibility and longer ADC settling. Keep signal wiring away from high-current lines and share a ground reference with your controller.

Designing Around the Open Wiper

If you’re specifying a membrane potentiometer, this is the most important integration detail on this page — it accounts for more support questions than everything else combined.

A membrane potentiometer’s wiper is not connected to the resistive track until something presses on it. Untouched, the wiper terminal is an open circuit. Connect it straight to a microcontroller ADC and the pin floats — you’ll read drifting nonsense that looks convincingly like a broken sensor. It isn’t. It’s the part working as designed.

Three ways to handle it, with honest trade-offs:

1. Pull-down resistor (simplest). A resistor from wiper to ground — commonly 100 kΩ — gives a defined low reading when untouched. Cost: it forms a divider with the sensor, so you lose output range and introduce slight non-linearity. Pick the largest value that still gives a reliable untouched reading.

2. Series resistor plus internal pull-up. A series resistor from supply into the sensor, combined with the microcontroller’s internal pull-up, produces a distinctly high untouched reading well outside the pressed range. Cost: roughly half your output swing. Benefit: untouched becomes unambiguous, so you can’t confuse “not touched” with “touched at position zero.”

3. Comparator plus sample-and-hold (best behaviour). Use a comparator to detect whether the sensor is touched at all, and gate a sample-and-hold on the position output with it. You get a clean touch/no-touch flag and retain the last valid position after release. Cost: a few more components. Benefit: it treats “untouched” as information rather than a fault to suppress — which is usually what it is.

A 0.1 µF capacitor on the analog input helps with noise in all three cases. Whichever you choose, decide it at schematic stage — retrofitting onto a finished board is where this gets painful. For measuring the sensor itself, see How to Test a Potentiometer.

The Wiper Is a Component, Not an Accessory

For membrane sensors, wiper selection is a design decision with real consequences. The standard recommendation is a Delrin tip applying 1–3 newtons — too little force gives intermittent contact, too much accelerates wear. Material and tip geometry both affect life cycle and electrical output, so unusual environments or demanding cycle counts are worth a conversation before you commit. A purpose-made threaded wiper is available, though many applications use their own actuator geometry successfully.

Typical Applications

• Medical devices — thin, sealed, cheap enough for disposable instrumentation, in configurations that survive sterilization (Medical-Grade Position Sensors: EtO and Autoclave Sterilization).
• Industrial automation — valve position, actuator stroke, fixture travel. Rod-style where there’s room; membrane where there isn’t.
• Hydraulics and pneumatics — contactless gives full-travel cylinder position where reed switches give only end-of-stroke, without breaching the cylinder.
• Automotive and motorsport — damper travel, ride height, pedal position. Cycle life and temperature decide; mounting envelope constrains.
• Robotics — joint and slide feedback where absolute position after power-up beats ultimate precision.
• Audio, visual and control interfaces — membrane sensors work as touch inputs as readily as position sensors: ribbon controllers, panel controls with no moving parts.
• Aerospace and test — sealed, low-mass sensing where a rigid sensor body is a weight and packaging penalty.

How to Choose a Linear Potentiometer

Work through these in order. Each step eliminates options; the early ones eliminate the most.

1. What kind of motion is it? Linear, or rotary somewhere in the mechanism? Check for a pivot or leadscrew you could measure instead. Above ~2 m of straight-line travel, look at string potentiometers.

2. Will it physically fit? Measure the mounting envelope at both extremes, not just the stroke. If a rigid body won’t fit at full compression, you need a membrane sensor — and it will fit essentially anywhere.

3. How much travel, and how precisely? Convert your linearity requirement into millimetres over your actual travel length. That one calculation usually narrows five options to two.

4. What’s the environment? Temperature first, then ingress. Above +50 °C means HotPot or MotionPot. Washdown, immersion, or a sealed vessel you can’t breach means contactless. Check actuation force at your coldest temperature, not at room temperature.

5. How many cycles over the product’s life? Multiply honestly. Past a million actuations, you want the 10-million-cycle parts.

6. Contact or contactless? Contactless eliminates wear at the sensing interface and lets the sensor sit outside the medium — at the cost of ±5% standard linearity and ~3 mm hysteresis. Worth it for cylinders and liquid level; not for precise positioning.

7. How does it connect? Solder tabs, male pins, or receptacle housings in plain, latch and detent variants. Match this to your harness early.

8. What’s the budget? Membrane sensors cost a fraction of rod-style industrial transducers, and far less than LVDTs. If you’ve been quoted several hundred dollars for a position sensor, check whether a membrane part does the job first.

When a Potentiometer Is the Wrong Choice

Choose something else for sub-micron repeatability (optical or interferometric scales), travel beyond a few metres (string pot or magnetostrictive), certified performance under severe vibration over decades (LVDT — genuinely better here), or digital fieldbus output with no analog input available (an encoder or smart transducer).

For most industrial, medical and embedded applications needing absolute position over a few millimetres to a couple of metres, a potentiometer remains the most cost-effective answer — and the only one that knows where it is the instant you power it up.

Frequently Asked Questions

Ready to Specify a Part?

Spectra Symbol manufactures the full range covered here — membrane, narrow-format, high-temperature, contactless magnetic, and rod-style linear motion potentiometers — in stock lengths and custom configurations, with electrical travel from 8 mm to 2000 mm.

Shop linear potentiometers and linear position sensors

Need something outside the standard range? Length, shape, resistance, track count and connector style can all be customised. Start a custom sensor design

Recommended Next Reads

• How to Wire a Potentiometer: Step-by-Step Diagrams & Guide
• Potentiometer Wiring and Pinout
• How to Test a Potentiometer
• How Magnetic Position Sensors Work
• Encoder vs Potentiometer
• Exploring Spectra Symbol Potentiometers — the full range, including flex and rotary sensors