AMR Sensors (Magnetic Sensors）Glossary: AMR sensors (magnetic sensors)

A-B-C

Active magnetic field

• This is the strength of the magnetic force where the AMR sensor turns on (or off), and it is specified in units of mT (millitesla).
• The ON sensitivity (Hon) is the magnetic force that turns on the sensor which was off with a weak magnetic field, the OFF sensitivity (Hoff) is the magnetic force that turns off the sensor which was on with a strong magnetic field, and H stands for the magnetic flux density.

AMR

Analog output

• In most AMR sensors, the output is Hi/Lo digital output and is used for switch applications, but some sensors include products consisting of elements only, and the output voltage is output as an analog signal. These sensors are not for all-purpose applications.
• Consider a digital output type with an internal processing circuit.

Chattering

Current consumption

• This is the current used by the AMR sensor to operate.
• This is the current used when it flows to the IC circuit and magnetic resistors in the sensor.
• The current consumption depends on the supply voltage. A larger supply voltage results in a higher current consumption.

D-E-F

Elements

• Elements refer to the analog outputs.
• In the sensor, analog output is used to detect how the magnet approaches the sensor and the rotating position of the magnet.
  The analog output can provide higher resolution results depending on the performance of the signal processor.

Ferromagnetic metal

• The magnetic resistor section of the AMR sensor is a thin film of alloy consisting of nickel, iron, copper, and other substances, and this alloy is ferromagnetic metal.
• In ferromagnetic metal, the electrical resistance changes based on an external magnetic field.
• When ferromagnetic metals are subjected to an external magnetic field, at the molecular level, rotation in the 3d-band electron orbital plane occurs, and combined with the interaction of the inherent spin orbit of the electrons, this causes distortion in the 3d-band electron distribution (d-band wave function is distorted). As a result, the electrons seek energy stability, and this incites a change in the conduction electron probability of occurrence in the 4s-band, which is a different electron orbit, and this state is manifested as a change in electrical resistance.

G-H-I

Hoff

Hon

M-N-O

Magnetoresistance effect

mT

Non-contact

• Non-contact indicates that operations can be performed without direct contact.
• For AMR sensors, boards with installed sensors are contained in the product, and this enables usage for the following applications.
  • Sensors that are not directly visible.
  • Switches that are easily adaptable into a waterproof structure
  • Switches that you do not want to reveal to the user
  Their properties allow an extremely wide range of applications, such as enabling operation from outside the sensor when the case is made of materials where magnetic forces pass through.
• Locations that use reed switches have contacts, but AMR sensors do not have any contacts. In locations with harsh operating environments, such as those subjected to impacts or vibrations, AMR sensors can provide higher reliability. In some cases, the same magnet as the reed switch can be used without any modifications.

P-Q-R

Permalloy

Resistance value

• AMR sensors use resistors that change based on the magnetic force.
• Resistance values vary by the product, but they can range from several hundred Ω to several hundred kΩ. They change by up to 3% based on the size and direction of the magnetic force.
• Whereas higher resistance values have the advantage of reducing the current consumption, they result in longer current paths, and so larger sizes are required for the element. Narrow elements can lead to process stability issues and the inability to obtain sufficient changes.
  Murata Manufacturing's AMR sensors exemplify our cutting-edge techniques for developing and providing sensors with compact sizes and low power consumption.

Response frequency (drive cycle)

S-T-U

Sensitivity

Temperature characteristics

V-W-X

Variation in sensitivity

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