Durable, Affordable, or Precise: Choosing the Right Magnetic Position Sensor

Author: David Marriott, Spectra Symbol CEO

In project management they say “good, fast or cheap–pick two, but never all three”. This concept, known as the Iron Triangle, gets at the idea of tradeoffs between the main factors of any given project. In engineering and manufacturing, picking the right part is more of a trade-off between the factors of durability, affordability, and precision.

Mismatching these priorities for your application can mean ending up with a part that’s overkill for what you need, wears out quickly, or puts unnecessary strain on the budget. This guide analyzes the four main types of magnetic position sensors and their rankings and trade-offs in the areas of durability, affordability, and precision.

When looking at sensors in general, Dr Iyengar of Florida International University classified them based on whether they were active or passive, referring to their power dependency, and whether they were analog or digital, referring to the type of output they provide. We borrow from this typology for classification purposes, but have added the subcategories of position measured and measurement requirements specific to position sensors. For more information, see this helpful typology by NYBSYS.

Category	Subtype	Description
Power Dependency	Active	Require external power (e.g., Hall-effect sensors)
	Passive	Generate a signal without external power (e.g., magnetoresistive sensors)
Response Output	Analog	Continuous signal, suitable for high-precision tracking
	Digital	Discrete signal, often used for limit switching or binary detection
Position Measured	Linear	Measures displacement in a straight line
	Rotary	Tracks rotational motion
	Angular	Measures tilt or angular displacement
Measurement Requirements	Contact	Physical interaction (e.g., potentiometric sensors)
	Non-contact	Uses magnetic, optical, or inductive sensing

Other Types of Position Sensors

Different types of sensors rely on distinct physical principles to detect movement and position. Each technology has its strengths and limitations, making selection crucial for specific applications. For a more comprehensive look at each type, see this helpful resource by Monolithic Power.

Inductive (magnetic-based) – Operates like a metal detector, well-suited for harsh environments and metallic targets.
Capacitive – Functions similarly to touchscreen technology, ideal for high-resolution position tracking but sensitive to environmental changes.
Optical – Provides exceptional accuracy but is highly susceptible to dust, dirt, and obstructions.
Potentiometric – Uses a resistive track and a moving wiper, offering straightforward and precise position tracking.

Magnetic Position Sensors

Magnetic position sensors use the interaction between a sensor element and a magnetic field to determine position. They are widely used in industrial automation, robotics, and automotive applications due to their durability and ability to function in harsh environments.

These position sensors can be classified into four main options: Hall Effect sensors, magnetoresistive sensors, Reed switches, and the MagnetoPot. Their capacities within our framework are as follows:

Sensor Type	Power Dependency	Response Output	Position Measured	Measurement Requirements
Hall Effect	Active	Analog & Digital	Linear, Rotary, Angular	Non-contact
Magnetoresistive	Active	Analog & Digital	Linear, Rotary, Angular	Non-contact
Reed Switch	Passive	Analog	Linear, Rotary	Non-contact
MagnetoPot	Passive	Analog	Linear, Rotary	Non-contact

Each operates on different principles and varies in precision, durability, output, environmental suitability, and cost.

1. Magnetoresistive Sensors

Magnetoresistive sensors are active sensors that measure resistance changes in response to magnetic fields, providing high-precision analog and digital outputs. The voltage output changes as the magnetic resistance changes with the magnet’s position.

They can detect linear, rotary, and angular positions with exceptional sensitivity and accuracy, making them ideal for demanding applications. There are three main types:

AMR Sensors (Anisotropic Magnetoresistive) offer higher precision than Hall Effect sensors and Reed switches, reaching sub-micron accuracy. They are durable, cost-effective, and commonly used in motor control, automotive steering angle detection, and industrial automation.
GMR Sensors (Giant Magnetoresistive) provide even greater sensitivity, often in the nanometer range, making them well-suited for robotics, medical devices, and HDD read heads. Though more expensive than AMR sensors, they offer high precision for fine position control.
TMR Sensors (Tunnel Magnetoresistive) leverage quantum tunneling effects for ultra-high accuracy, excellent stability, and low power consumption. They excel in industrial automation, consumer electronics, and advanced automotive applications but are the most expensive of the three.

Magnetoresistive sensors are highly durable and perform well in extreme conditions, making them essential for aerospace, medical devices, and high-precision manufacturing. However, they are generally more expensive than Hall Effect sensors.

2. Hall Effect Sensors

Hall Effect sensors are active sensors that generate a proportional voltage based on changes in a magnetic field. They operate on a very similar principle as magnetoresistive sensors, but inverted–you see a change in voltage rather than in resistance. Hall Effect sensors offer moderate precision (micrometer range), strong durability due to their solid-state design, and both analog and digital outputs.

Capable of measuring linear, rotary, and angular positions with non-contact operation, they are widely used in automotive applications such as throttle position and steering angle detection, as well as industrial automation.

Their resistance to dust and moisture makes them ideal for harsh environments, and they are among the most cost-effective magnetic position sensors. For more on Hall Effect sensors, see this article.

3. Reed Switches

Reed switches are passive sensors that require no external power and provide simple digital on/off output. They differ from magnetoresistive and Hall Effect sensors in that they are more mechanical than electronic and have a moving part. They use two ferromagnetic contacts sealed in a glass tube that close or connect in the presence of a magnetic field, making them ideal for detecting when a magnetic field is nearby.

This creates a very simple, on-off connection with less precision and relative position information than you would get with a Hall Effect or magnetoresistive sensor. This can be mitigated by lining up several Reed switches along a line to get a sense of their relative position, but it may be simpler to use a different sensor altogether.

While less precise than Hall Effect or magnetoresistive sensors, they are highly durable and operate reliably in extreme conditions. Reed switches are the simplest of the magnetic type sensors. Their resistance to humidity and explosive environments makes them well-suited for security systems, fluid level detection, and industrial automation.

With low cost and passive operation, Reed switches are a practical choice for applications that prioritize durability over precision.

4. MagnetoPot

MagnetoPot sensors are passive, analog-output sensors designed for linear position tracking. This sensor is less well-known and stands for magnetic potentiometer. It is a potentiometer, or a variable resistor, that is actuated with a magnet. MagnetoPots combine potentiometric and magnetic sensing principles, enabling smooth, contactless position feedback without mechanical wear.

An external magnet connects to an internal magnet within the linear path of the MagnetoPot and outputs a resistance reading in ohms. As the external magnet moves along the path, the resistance reading gives you a continuous reading. This is particularly advantageous when you need to measure something through a wall. Unlike Reed switches, which provide only binary on/off detection, MagnetoPot sensors output a continuous analog voltage signal, making them a more precise contactless position sensor while remaining more cost-efficient than advanced magnetoresistive sensors.

Their durability and resistance to environmental wear make them particularly effective for fluid-level sensing in oil, gas, and hydraulic applications. With a moderate cost, they offer a balance between affordability and performance, making them a practical choice for robust industrial positioning needs.

Conclusion

Choosing the right magnetic position sensor isn’t just about picking the most advanced option or the cheapest one—it’s about finding the best fit for your specific application. If you just need a simple on/off switch, a Reed switch might be do the trick. If precision is a priority, Hall Effect and magnetoresistive sensors offer more accuracy, with TMR sensors leading the pack for high-precision tracking. MagnetoPot sensors bring a unique blend of analog output and magnetic actuation, making them a solid choice for linear position tracking, especially when measuring through surfaces.

Sensor Type	Precision	Durability	Environmental Suitability	Cost
Reed Switch	Low	Moderate (mechanical wear)	Suitable for basic applications	Low
AMR	Moderate	High	Good temperature stability	Moderate
GMR	High	High	Strong magnetic sensitivity	High
TMR	Very High	Very High	Excellent in harsh environments	High
Hall-Effect	Moderate	High	Affected by temperature variations	Low to Moderate
MagnetoPot (magnetic potentiometer)	Moderate	Moderate (wear over time)	Limited to clean environments	Low

At the end of the day, it all comes down to the trade-offs between precision, durability, and cost. Knowing the strengths and limitations of each type of sensor and then matching those to the needs of your application can help you avoid a match that’s overpowered, wears out quickly, or unnecessarily stretches your budget.