Why a Linear Position Sensor Shouldn’t Be Selected by Stroke Alone

🧩 Further Reading – Measurement as a System

This article is part of an engineering series exploring how reliable measurement depends on proper system design rather than on a single sensor component.

Before diving deeper into industrial temperature sensing, you may also find the following articles in the series useful:

VARIOHM Group – When Measurement Is a System, Not a Component
How to Select Sensors for Harsh Environments: An Engineering Guide for Reliable Measurement in the Real World
VARIOHM Position Sensors – Engineering Position as a System, Not Just a Signal
Industrial Pressure Sensors – When Pressure Measurement Becomes a System Engineering Challenge
Industrial Temperature Sensors – When Temperature Measurement Becomes a System Engineering Challenge
Choosing the Right Linear Position Sensor: Why Stroke Length Is Only the Beginning
Contactless Rotary Position Sensors – Why More and More Systems Are Moving to Non-Contact Sensing
Choosing the Right Temperature Probe Mounting
How Differential Pressure (ΔP) Can Reveal Problems Long Before a System Shuts Down
Your Temperature Sensor Says 80°C. The Real Hot Spot Could Already Be at 130°C
Measuring Pressure Without Temperature Is Only Half the Picture
Does Your Thermal Protector Really Solve the Problem? Or Just Give the System Another Chance to Fail?

Choosing a Linear Position Sensor in Four Steps

Before selecting a part number, take a moment to answer the following four questions.

In most cases, working through them in this order will lead you to the right sensor family far more effectively than starting with the stroke.

Step 1 – How Does Your System Actually Move?

What type of motion are you measuring?

⬜ Simple linear motion

⬜ Long stroke

⬜ High duty cycle / frequent movement

⬜ Vibration or side loads

⬜ Space-constrained installation

👉 Understanding the motion is more important than knowing the stroke length.

Step 2 – What Mechanical Constraints Do You Have?

What is the biggest mechanical limitation?

⬜ Limited installation space → ELPM / KTP

⬜ Pull rod design required → PCM / KTC

⬜ No room for an external rod → KTF

⬜ No significant mechanical constraints → Continue to Step 3

Step 3 – What Matters Most in Your Application?

Define your priorities.

✅ Cost-effective solution → IPL / VLP / VXP

✅ Compact design → ELPM

✅ High temperature stability → KTP

✅ Long stroke applications → KTC / KTF

✅ General industrial use → PCM

Step 4 – Only Now Ask: What Stroke Do I Need?

Once you understand:

✔ How the system moves

✔ The mechanical installation constraints

✔ The operating environment

✔ Which sensor family best matches the application

…you can select the appropriate stroke length.

The Bottom Line

Most engineers start by asking:

“What stroke do I need?”

In reality, that should be one of the last questions.

Because a linear position sensor should not be selected solely by the distance it measures.

It should be selected for the life it is expected to live.

A Linear Position Sensor Shouldn’t Be Chosen by the Distance It Measures

When engineers begin looking for a linear position sensor, the first question is almost always the same:

What stroke do I need?

50 mm?

250 mm?

1000 mm?

It’s an important question.

But it only tells you how far the sensor needs to measure.

It tells you nothing about the life that sensor is about to live.

It doesn’t tell you how many times it will move each day.

It doesn’t tell you whether the rod will be exposed to side loads.

It doesn’t tell you whether the machine will vibrate for 20 hours a day.

It doesn’t tell you whether the sensor will operate in dust, oil, changing temperatures, or inside a machine where every millimetre of installation space matters.

And that’s exactly why two sensors with the same stroke can be the right choice for two completely different applications.

Engineers design around distance.

Sensors live according to their operating conditions.

Two Machines. The Same Stroke. Two Completely Different Worlds.

Imagine two systems that both require a measurement range of 500 mm.

System A

The axis moves twice a minute.
The machine operates in a climate-controlled production hall.
Vibration is minimal.
The mechanism is precisely aligned.
Access to the sensor is easy.

System B

The axis cycles dozens of times per minute.
The machine runs almost continuously.
Constant vibration and mechanical shock are present.
Dust, oil and temperature fluctuations are part of everyday operation.
Access to the sensor is limited.
Every unexpected shutdown results in expensive production downtime.

Looking only at the stroke, both applications appear to require exactly the same sensor.

In reality, they have very little in common.

The distance is identical.

The sensor’s life will be completely different.

Stroke Tells You How Far-Not How

Stroke defines the measurement range.

It does not describe how the system moves.

It doesn’t tell you whether the motion is smooth or aggressive.

It doesn’t tell you whether you’re measuring a pneumatic cylinder, an electric actuator, a packaging machine, agricultural equipment, or a heavy industrial system.

Nor does it tell you whether the motion will remain perfectly linear throughout the machine’s life.

In real-world applications, systems change over time.

Side loads develop.

Misalignment appears.

Mechanical play increases.

The rod may experience slight bending.

Vibration becomes part of every operating cycle.

Bearings and mechanical joints gradually wear.

Every one of these factors influences how a position sensor performs.

And in many applications, they have a far greater impact than the difference between a 250 mm stroke and a 300 mm stroke.

A Sensor That Fits on Day One May Not Fit Five Years Later

On installation day, everything is new.

The shafts are perfectly straight.

The bearings have no play.

The mechanism is correctly aligned.

The wiring is neatly installed.

The operating temperature is under control.

But machines don’t stay new.

After hundreds of thousands-or even millions-of operating cycles, small changes begin to appear.

A bearing develops slight wear.

A linkage gains a little play.

A cylinder no longer pulls perfectly in line.

The machine frame absorbs vibration year after year.

Individually, none of these changes is usually enough to stop production.

Together, however, they can completely change the operating conditions of the position sensor.

That’s why the real question isn’t simply:

“Does the sensor cover the required stroke?”

It’s:

“Is this sensor designed for the way the machine will operate throughout its lifetime?”

Not Every Application Needs the Most Advanced Technology

It’s easy to assume that the most sophisticated—or most expensive—sensor is automatically the best choice.

In reality, that’s rarely true.

For many applications, a linear potentiometric position sensor is an excellent solution.

It can be simple, reliable, accurate and cost-effective.

Other applications, however, involve extremely high duty cycles, limited installation access or demanding maintenance requirements.

In those cases, a different sensor design -or even a different sensing technology-may be the better engineering choice.

The goal isn’t to select the most impressive sensor on paper.

The goal is to select the sensor that best solves the real engineering problem.

Why So Many Different Linear Position Sensor Families Exist

If stroke were the only parameter that mattered, manufacturers would only need a handful of sensor models.

In reality, there are many different sensor families because each one is designed to solve a different engineering challenge.

Not every sensor is intended to solve the same problem.

Some applications have severe space limitations.

Others are driven primarily by cost.

Some require short strokes.

Others require one metre, two metres or even three metres of travel.

Some machines are mechanically suited to a pull rod design.

Others simply don’t have room for an external rod, making a rodless design the better solution.

That’s why sensor selection shouldn’t begin with a catalogue.

It should begin with the machine.

When Installation Space Is Limited – ELPM and KTP

In many applications, the challenge isn’t the stroke length.

The challenge is finding enough space to install the sensor.

A sensor may meet every electrical requirement – stroke, accuracy and output signal – yet still be impossible to integrate because its mechanical dimensions don’t fit the available space.

This is exactly where compact sensor families become the right solution.

ELPM Linear Position Sensor

The ELPM series offers linear position measurement with strokes of up to 175 mm.

It is particularly well suited for applications where installation space is limited and a compact sensor is required without compromising measurement performance.

KTP Position Sensor

The KTP series is designed for applications where installation space is extremely limited while maintaining excellent temperature stability.

In these applications, selecting a sensor based solely on stroke may result in a product that measures the required travel but simply doesn’t fit the available mechanical envelope – or cannot maintain stable performance across the required operating temperature range.

When Cost and Simplicity Matter – IPL and VLP / VXP

Not every application requires the most sophisticated solution.

Very often, the best engineering choice is a simple, reliable linear potentiometric sensor.

IPL Linear Position Sensor

The IPL series provides linear position measurement with strokes of up to 1000 mm and is designed as a cost-effective solution.

It is an excellent choice when:

Application requirements are straightforward.
Operating conditions are well suited to potentiometric technology.
Cost is an important consideration.
There is no justification for a more complex sensing solution.

VLP / VXP Linear Potentiometers

The VLP and VXP series offer potentiometric linear position sensing with strokes of up to 250 mm.

They are well suited for applications requiring a simple, proven and reliable method of measuring linear movement.

The important point isn’t that potentiometric technology is “less advanced.”

The important point is that, in the right application, it may be the best engineering solution available.

When a Pull Rod Design Is Required – KTC and PCM

In many machines, the mechanical design determines the correct sensor.

When a pull rod configuration best matches the motion and geometry of the application, the sensor should be designed for that type of installation.

KTC Linear Motion Position Sensor

The KTC series offers pull rod sensors with strokes of up to 1250 mm.

It is particularly suitable for applications requiring long linear travel using a pull rod configuration.

The decision to choose KTC isn’t based on stroke alone.

It’s based on whether a pull rod design is the best mechanical solution for the application.

PCM Linear Motion Position Sensor

The PCM series offers pull rod sensors with strokes ranging from 50 mm to 900 mm.

It provides a versatile solution for a wide variety of industrial applications.

However, stroke should never be the only selection criterion.

Motion characteristics, installation constraints, duty cycle and mechanical loading should all be considered before making the final choice.

Two sensors may offer exactly the same stroke.

But if only one integrates properly into the machine’s mechanical design, they are not truly equivalent alternatives.

When Long Stroke Applications Leave No Room for an External Rod – KTF

Long stroke applications introduce another mechanical challenge.

A conventional pull rod sensor requires additional installation space to accommodate the full extension of the rod.

As stroke length increases, this can quickly become impractical.

In these situations, a rodless design may offer a far more effective solution.

KTF Linear Motion Position Sensor

The KTF series provides linear position measurement with strokes of up to 3000 mm using a rodless design.

This is more than simply offering a longer stroke.

It is a fundamentally different mechanical concept, designed for applications where an external rod would be impractical, difficult to install or incompatible with the available installation space.

It’s a perfect example of why the real question isn’t simply:

“How far do I need to measure?”

It’s:

“What’s the best way to measure that distance inside my machine?”

The Same Stroke Doesn’t Mean the Same Sensor

Imagine your application requires a stroke of 150 mm.

At first glance, several sensor families may appear suitable.

The correct choice depends entirely on the application.

If installation space is limited, ELPM or KTP may be the best fit.
If a simple and cost-effective potentiometric solution is preferred, IPL or VLP / VXP may be ideal.
If the machine is designed around a pull rod mechanism, PCM or KTC may provide the best mechanical integration.
If a long travel without an external rod is required, KTF may be the right solution.

The measurement distance is identical.

The engineering solution is not.

Because a position sensor should never be selected by a number alone.

It should be selected for the environment, the mechanics and the life it is expected to live.

Questions to Ask Before Selecting a Linear Position Sensor

Before choosing a specific model, ask yourself:

How does the machine actually move?

Is the motion smooth and truly linear, or are there side loads, mechanical play or alignment issues?

What is the expected duty cycle?

A sensor that moves once an hour lives a very different life from one that cycles dozens of times every minute.

What operating environment will it face?

Will it be exposed to vibration, shock, dust, oil, moisture or significant temperature changes?

How much installation space is available?

Can the application accommodate a pull rod, or would a compact or rodless design be more appropriate?

What is the cost of downtime?

If replacing the sensor is difficult or production downtime is expensive, the purchase price is only a small part of the overall cost.

Does the application really require a more sophisticated technology?

In many cases, a straightforward potentiometric sensor is the best engineering solution.

In others, the operating conditions justify a different sensing technology or mechanical design.

Only after answering these questions should you ask:

“What stroke do I need?”

Conclusion

Stroke is an important specification.

But it only defines the measurement range.

It doesn’t describe the motion.

It doesn’t describe the environment.

It doesn’t describe the mechanical loads.

And it certainly doesn’t describe the life the sensor is expected to live.

That’s why a linear position sensor shouldn’t be selected solely by the distance it measures.

It should be selected for the machine in which it will operate.

For the way it moves.

For the way it will be installed.

For its duty cycle.

And for the operating conditions under which it must continue delivering reliable position measurements year after year.

The next time you’re selecting a linear position sensor, don’t just ask:

“How far does it need to measure?”

Ask instead:

“What kind of life will this sensor have?”

Because the stroke is listed in the catalogue.

Real life begins after the sensor is installed.

Which Sensor Family Fits Your Application?

If your challenge is…	Recommended Series	Why?
Limited installation space	ELPM	Compact design, stroke lengths up to 175 mm
Limited space with high temperature stability	KTP	Compact sensor designed for applications with significant temperature variations
Cost-effective solution for long strokes	IPL	Linear potentiometric sensor with stroke lengths up to 1000 mm
Simple, reliable potentiometric solution	VLP / VXP	Cost-effective linear potentiometers with stroke lengths up to 250 mm
Long stroke applications requiring a pull rod	KTC	Pull Rod design, stroke lengths up to 1250 mm
Long stroke applications with no room for an external rod	KTF	Rodless design, stroke lengths up to 3000 mm
General industrial linear motion applications	PCM	Pull Rod design, stroke lengths from 50 to 900 mm

Important: Every sensor family above measures linear position. The real difference isn’t just the stroke – it’s the mechanical design, installation constraints, operating environment and the specific requirements of the application.

Case Studies – When the Stroke Was Right, but the Sensor Wasn’t

The following examples are based on typical engineering scenarios and demonstrate how operating conditions can have just as much influence on sensor selection as the required stroke itself.

Case Study 1 – The Stroke Was Correct, but the Sensor Wasn’t Designed for the Real World

A machine builder selected a standard pull rod linear position sensor from a generic manufacturer.

On paper, the sensor met every system requirement:

Stroke: 175 mm
Accuracy: ±0.5%
Output: 0-10 V
Protection: IP65

During development, the system performed perfectly.

Once installed at the customer’s facility, however, the operating conditions were very different:

22 hours of operation per day
Approximately 4 million operating cycles per year
Continuous vibration from the drive system
Moderate side loads developing during normal operation

After approximately 14 months, the system began showing position deviations of ±0.8 mm.

The sensor was replaced.

For about two months, everything appeared to be back to normal.

Then the same problem returned.

A detailed investigation revealed that the issue wasn’t the stroke at all.

The application required a sensor specifically designed for continuous industrial operation, with a pull rod construction capable of handling the mechanical loads generated by the machine.

After replacing the original sensor with a PCM-175, the system returned to stable operation – without any changes to the software, controller or mechanical design.

Key takeaway: Sometimes the difference isn’t the stroke length. It’s whether the sensor is designed for the real life of the machine.

Case Study 2 – The Problem Wasn’t Measurement Accuracy. It Was Space.

A medical equipment manufacturer was developing a compact mechanism requiring only 10 mm of linear travel.

The engineer selected a sensor with a 10 mm stroke, assuming that any sensor with the correct measuring range would fit.

Only during final assembly did the real problem become apparent.

Although the measuring range was correct, the sensor required an additional 18 mm of installation space behind the mounting point – space that simply wasn’t available inside the enclosure.

The result was a mechanical redesign of the assembly, project delays and additional engineering costs.

By switching to the KTP-10-L, the sensor fitted perfectly within the existing enclosure, eliminating the need for any mechanical modifications.

Key takeaway: The stroke was correct from day one. The available installation space wasn’t considered.

Case Study 3 – When Service Life Matters More Than Stroke

An automotive test equipment manufacturer was developing a suspension testing system.

The application requirements were relatively straightforward:

Stroke: 50 mm
Operating frequency: 18 Hz
Approximately 1.5 million operating cycles per month

The original position sensor was selected primarily based on stroke length and measurement accuracy.

During the first months of testing, everything performed as expected.

After several months of continuous operation, however, measurement noise began to appear, reducing the repeatability of the test results.

In this case, the issue wasn’t measurement accuracy.

It was sensor service life.

The system was upgraded to the ELPM-50, a sensor specifically designed for demanding dynamic applications.

Key features include:

IP67 environmental protection
Mechanical life exceeding 25 million operating cycles
Maximum operating speed of up to 10 m/s
Operating temperatures up to 150°C
Lightweight, robust aluminium housing

The result was a stable measurement system capable of maintaining reliable performance throughout continuous operation.

Key takeaway: When a sensor performs millions of operating cycles, the important question isn’t just how far it measures – it’s how long it can continue measuring with the same level of performance.

Quick Guide: 8 Questions to Ask Before Selecting a Linear Position Sensor

Before selecting a part number or comparing prices, take a moment to answer the following questions. In many cases, the answers will have a much greater impact on sensor selection than the required stroke itself.

1. How Does Your System Actually Move?

Is the motion truly linear, or will the sensor be exposed to side loads, vibration, shock or misalignment?

The way the machine moves has a direct impact on both sensor selection and long-term reliability.

2. Does the Required Stroke Include a Safety Margin?

Don’t select a sensor based solely on the nominal working travel.

Consider overtravel, tolerances and worst-case operating conditions that may occur during the machine’s lifetime.

3. What Level of Accuracy Is Really Required?

Not every application requires extremely high absolute accuracy.

In many systems, repeatability is more important than absolute accuracy, particularly in applications involving repetitive motion.

4. What Operating Environment Will the Sensor Face?

Consider the following:

Operating temperature
Dust and contamination
Oil and process fluids
Moisture or water exposure
Vibration and mechanical shock

Environmental conditions often have just as much influence on sensor performance as the electrical specifications.

5. Is There Enough Installation Space?

Sometimes the real limitation isn’t the stroke length – it’s the available installation space.

In some applications, a compact sensor is the best choice. In others, a Pull Rod or Rodless design may provide a better mechanical solution.

6. Is the Output Signal Compatible with Your Control System?

Verify that the sensor provides the required interface, such as:

0-10 V
4-20 mA
Ratiometric output
Digital interfaces (where required)

Selecting the correct output from the beginning can eliminate unnecessary signal converters and simplify system integration.

7. Is the Electrical Infrastructure Suitable?

Check the following:

Supply voltage
Connector type
Cable length
EMC compatibility
Electrical noise levels within the system

In industrial and mobile equipment, these factors can significantly affect measurement stability.

8. What Will the Sensor’s Life Look Like Five Years from Now?

This may be the most important question of all.

How many operating cycles are expected?
How difficult will the sensor be to replace?
What is the cost of machine downtime if the sensor fails?

Sometimes the more expensive sensor is actually the most economical choice because it reduces maintenance, service calls and production downtime over the life of the machine.

The Bottom Line

Selecting a linear position sensor doesn’t begin with a catalogue.

It begins with understanding the application.

When you consider the motion, operating environment, mechanical design and expected service life, choosing the right sensor family – whether ELPM, KTP, IPL, VLP/VXP, PCM, KTC or KTF – becomes much more straightforward.

Stroke is only the starting point.

The application determines the right sensor.

FAQ – Frequently Asked Questions About Selecting Linear Position Sensors

Is stroke the most important parameter when selecting a linear position sensor?

No.

Stroke defines the required measuring range, but it doesn’t describe the sensor’s operating conditions. Factors such as side loads, vibration, temperature, operating environment, duty cycle and mechanical installation are just as important when selecting the right sensor.

Can two sensors with the same stroke be suitable for completely different applications?

Absolutely.

Two sensors may offer the same stroke, output signal and even similar accuracy, yet be designed for entirely different applications. The sensor’s mechanical design, installation method and durability ultimately determine whether it is the right choice.

When should I choose a compact position sensor?

A compact sensor is often the best choice when installation space is limited or the machine design cannot accommodate a longer sensor. In these situations, sensor families such as ELPM or KTP may provide the most suitable solution.

When is a potentiometric position sensor the right choice?

In many applications, a linear potentiometric sensor is an excellent solution.

When the operating conditions are appropriate and there is no need for a more sophisticated sensing technology, sensor families such as IPL or VLP / VXP provide a reliable, straightforward and cost-effective solution.

What’s the difference between Pull Rod and Rodless sensors?

Pull Rod sensors use a mechanical rod that moves together with the machine and are widely used in industrial linear motion applications.

Rodless sensors measure position without an external moving rod, making them particularly suitable for long stroke applications or installations where space is limited.

Should I always choose the most accurate sensor?

Not necessarily.

Accuracy is only one part of the selection process. In many applications, long-term reliability, mechanical compatibility and durability under real operating conditions are more important than achieving the highest possible accuracy.

How do vibration and side loads affect a position sensor?

Vibration, side loads and misalignment can reduce measurement quality, accelerate mechanical wear and shorten sensor life.

That’s why real operating conditions should always be considered during the design phase – not only the required stroke.

Should price be the main selection criterion?

No.

The purchase price is only a small part of the overall system cost.

Production downtime, service calls, sensor replacement and recalibration often cost far more than the difference between two sensor models.

How do I choose the right sensor family?

The correct choice depends on several factors, including:

Required measuring range (Stroke)
Motion characteristics
Mechanical installation
Operating environment
Expected duty cycle
Output signal requirements
Space and maintenance constraints

Only after evaluating these factors should you select the most appropriate sensor family, whether it’s ELPM, KTP, IPL, VLP / VXP, PCM, KTC or KTF.

What’s the single most important question to ask before selecting a position sensor?

Instead of asking only:

“What stroke do I need?”

Ask yourself:

“Under what conditions will this sensor operate throughout its service life?”

In most cases, the answer to that question will lead you to the right sensor choice.

Glossary – Linear Position Sensors

Position Sensor

A sensor that measures the position of a moving object and converts its movement into an electrical signal that can be read by a controller, PLC or other control system.

Linear Position Sensor

A sensor designed to measure movement along a straight line (linear motion), such as the travel of a cylinder, shaft, door, electric actuator or other mechanical mechanism.

Stroke

The maximum travel distance that a sensor is designed to measure.

For example, a sensor with a 250 mm stroke can measure movement over a distance of 250 mm.

Important: Stroke defines the measuring range only. It does not determine whether the sensor is suitable for a particular application.

Accuracy

The degree to which the measured position matches the true position.

High accuracy is particularly important in applications where absolute position must be known precisely.

Repeatability

The ability of a sensor to return the same measurement repeatedly when the same movement is performed under identical conditions.

In many automation systems, repeatability is just as important – and sometimes even more important – than absolute accuracy.

Resolution

The smallest change in position that the sensor can detect.

Higher resolution allows smaller movements to be measured, but it does not necessarily indicate higher accuracy.

Pull Rod

A sensor design in which a mechanical rod extends from the sensor body and moves together with the mechanism being measured.

This is a common solution in industrial machinery, cylinders and automation equipment.

Rodless

A sensor design that measures position without an external moving rod.

Rodless sensors are particularly suitable for long-stroke applications or installations where there is insufficient space for a full rod extension.

Potentiometric Position Sensor

A position sensor that measures movement by detecting changes in electrical resistance.

Potentiometric technology is well established, reliable and cost-effective, making it suitable for a wide range of industrial applications.

Contactless Position Sensor

A position sensor that measures movement without mechanical contact between its internal sensing elements.

This design eliminates mechanical wear and is particularly suitable for applications with high duty cycles or demanding operating environments.

Side Load

A force applied to the sensor at an angle other than its intended direction of movement.

Side loads can accelerate mechanical wear, reduce service life and negatively affect measurement performance.

Misalignment

A condition in which the sensor and the moving mechanism are not perfectly aligned.

Even small alignment errors can introduce mechanical stress and reduce long-term measurement performance.

Overtravel

Movement beyond the sensor’s intended measuring range.

When selecting a sensor, overtravel and potential worst-case operating conditions should always be taken into consideration.

Duty Cycle

The frequency and pattern of operation throughout the application’s lifetime.

A sensor operating once per hour experiences very different conditions from one cycling dozens of times per minute.

Cycle Life

The number of operating cycles a sensor is designed to perform while maintaining its specified performance.

For dynamic applications, cycle life is one of the most important selection criteria.

IP Rating (Ingress Protection)

An international standard that defines the level of protection a sensor provides against the ingress of dust and water.

For example:

IP65 – Fully protected against dust and protected against water jets.
IP67 – Fully protected against dust and suitable for temporary immersion in water.

Analog Output

A continuous electrical signal representing the measured position.

Common output options include:

0-10 V
0-5 V
4-20 mA

PLC (Programmable Logic Controller)

An industrial controller used to automate and control machines and manufacturing processes.

The position sensor provides the PLC with the position feedback required for accurate machine control.

Total Cost of Ownership (TCO)

The total cost associated with owning and operating a sensor throughout its service life.

In addition to the purchase price, TCO includes maintenance, machine downtime, replacement costs, service calls and overall operating expenses.

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