Optical vs Magnetic vs Capacitive: How Different Linear Encoders Work

Linear encoders are essential components in industrial automation, CNC machines, semiconductor manufacturing, robotics, and metrology systems. These devices measure linear displacement with high precision and convert it into readable signals. Depending on the application requirements—such as resolution, cost, environment, and durability—three primary types of linear encoders are widely used: optical, magnetic, and capacitive.

This article explores how each of these technologies works, compares their strengths and weaknesses, and guides you in selecting the right linear encoder for your application.

What Is a Linear Encoder?

A linear encoder is a sensor-device combination that converts linear position into an electronic signal, which can be processed by digital readouts (DRO), programmable logic controllers (PLC), or motion controllers.

Linear encoders are crucial for:

• Position feedback in CNC machines

• Motion accuracy in linear actuator systems

• Closed-loop control in linear motors with encoders

• Measuring devices in laboratories or metrology equipment

Types include:

• Incremental linear encoder

• Absolute linear encoder

• Sealed linear encoder for harsh environments

Optical Linear Encoder: High-Resolution Accuracy

How Optical Linear Encoders Work

An optical linear encoder uses a light source and a photodetector to read the position from a glass or metal linear encoder strip patterned with transparent and opaque lines. Movement over the strip generates light/dark signals, which are translated into position.

How optical linear encoders work:

• A light source (LED) illuminates a scale

• Light passes through or reflects off the scale

• A photodetector converts this pattern into pulses or position data

Key Features

• Resolution: Offers high resolution, up to nanometers

• Accuracy: Exceptional, due to light-based detection

• Applications: Semiconductor tools, precision CNC machines, coordinate measuring machines (CMM)

Pros

• Extremely precise

• Immune to magnetic interference

Cons

• Sensitive to dust, oil, or condensation

• Requires clean environments

Magnetic Linear Encoder: Rugged and Reliable

How Magnetic Linear Encoders Work

A magnetic encoder linear system consists of a magnetic strip (scale) and a readhead with magneto-resistive or Hall sensors. As the encoder moves along the magnetic strip, the magnetic field changes, which is detected by the sensor.

How magnetic linear encoders work:

• Magnetic poles are embedded in a strip

• Sensor detects changes in the magnetic field

• Signal is converted to position data

Key Features

• Resolution: Moderate to high

• Durability: Excellent in harsh industrial settings

• Applications: Heavy machinery, injection molding, automotive automation

Pros

• Resistant to dirt, oil, and water

• Can be used in extreme temperatures

Cons

• Slightly lower resolution than optical

• May suffer from magnetic field interference

Capacitive Linear Encoder: Cost-Effective and Compact

How Capacitive Linear Encoders Work

A capacitive linear encoder operates using changes in capacitance between two elements. As one element moves, the variation in capacitance is detected and translated into position.

How does a capacitive linear encoder work:

• A grid pattern moves relative to a stationary sensor

• Capacitance varies as the pattern changes

• Signal is processed into position data

Key Features

• Resolution: Moderate

• Size: Very compact

• Applications: Consumer electronics, compact automation systems, linear slide tables

Pros

• Compact and low-cost

• Not affected by magnetic fields

Cons

• Susceptible to moisture and electrical noise

• Lower accuracy than optical encoders

Comparative Overview

Specialized Encoder Systems and Variants

Incremental vs Absolute Linear Encoders

• Incremental encoders produce pulses and require a home reference.

• Absolute encoders provide exact position immediately on power-up.

Line Driver Encoders

• Line drivers transmit signals over long distances with noise immunity, especially in sealed linear encoder setups.

Linear Motor with Encoder

• For direct-drive systems requiring high dynamic response and accuracy, pairing linear motors with high-resolution linear encoders is standard.

Linear Actuator with Encoder

• A linear actuator with encoder provides feedback for position control in robotics, lab automation, and precision dispensing.

Linear Encoder Integration

How to Connect a Linear Encoder with PLC

• Identify encoder type (analog, digital, or serial)

• Use compatible PLC input modules

• Use line driver if the encoder signal needs long-range transmission

How to Use a Linear Encoder

• Mount securely and align with motion path

• Power the sensor and connect to the controller

• Calibrate or home the system as needed

How to Test a Linear Encoder

• Use an oscilloscope or encoder tester

• Confirm expected pulse output or position data

• Check for drift or instability under motion

How to Make a Linear Encoder (DIY)

• Use basic optical strip + IR sensor for prototyping

• Not recommended for high-accuracy needs

What Does Line Encoding Mean in This Context?

Though line encoding in digital communication differs slightly, in linear encoders, it often refers to how position signals are encoded (e.g., quadrature, serial output, analog sine/cosine), impacting how they interface with PLCs or motion controllers.

Cost Considerations: Linear Encoder Price

Linear encoder price varies depending on:

• Technology (optical > magnetic > capacitive)

• Resolution

• Brand and sealing

• Interface (TTL, HTL, BiSS-C, etc.)

Expect pricing to range from:

• $30–$80 for capacitive encoder strips

• $100–$300 for magnetic encoder kits

• $300–$1000+ for optical high-resolution encoders

Which Linear Encoder Is Right for You?

Each linear encoder type—optical, magnetic, or capacitive—has distinct advantages tailored to specific environments and budgets:

• Choose optical linear encoders for high-precision and clean-room applications.

• Choose magnetic linear encoders for industrial, outdoor, or rugged environments.

• Choose capacitive linear encoders for compact or cost-sensitive devices.

When selecting, consider:

• Accuracy and resolution needed

• Environment conditions (dust, oil, humidity)

• Interface and control system compatibility

Need Help Choosing the Right Linear Encoder?

Whether you're integrating a linear optical encoder in a CNC system or need a magnetic encoder linear solution for heavy-duty automation, expert guidance can help avoid costly mistakes.

Contact our engineering team for a tailored recommendation.
Need samples or quotes? Ask about our latest linear encoder price list!