Glossary of Angle Detection

AKM Angle Sensors

Definition of Technical Terms

This page explains commonly used terms in the technical information for AKM's angle sensors.

AKM's rotation angle sensors can be used in combination with magnets in order to easily assemble non-contact encoders that are resistant to dirt, water, oil, and other contaminants. High angular accuracy can be achieved using the angle error calibration function built into the AK745x series.

Click here for technical information about rotation angle sensors, including a magnet selection guideline and the calibration function.

Off-Axis Configuration

An Off-Axis is a configuration where the sensor center is not located on the rotational axis as shown in the figure. This configuration enables the end of shaft to be used freely, so that it is available for dual shaft motors and hollow shaft motors. 

The AK7454 and AK7455 support Off-Axis configuration.

Shaft-End Configuration

A shaft-end configuration is where the magnet center and sensor center are aligned on the axis of rotation as shown below.

* Bz=0 if there is no misalignment in the Shaft-End

Sensor element

This is the element that actually detects the magnetic field within the IC package. The position of the sensor element will differ for each product. Please refer to the datasheet for each product for details on sensor element position. (Click Here for each Datasheets) In the Magnet Selection Guideline, the sensing element is also referred to simply as "sensor".

Gap

The sensor air gap is defined as the distance between the magnet surface and  the sensor element. The package air gap is defined as the distance between the magnet surface and  IC package surface. Since the distance from the IC package surface to the sensor element position is different for each product, the package air gap used in the explanation for each product is sometimes referred to simply as "the gap."

In the Magnet Selection Guideline, (a technical document common to the AK74xx series of rotation angle sensors), the sensor air gap is also referred to simply as "the gap".

Magnetic Field (Bx, By)

Bx and By are the magnetic field components detected by the AK74xx, which are parallel to the surface of the IC.

* Bz=0 if there is no misalignment in the Shaft-End

MAG and Operating Magnetic Field Range

MAG is defined as  MAG = √ (Bx2+By2 +Bz2)

The magnetic flux density range needed to detect the rotation angle is called the operating magnetic field range. The operating magnetic field range of the AK74xx is from 30 to 70 mT for a shaft-end configuration. If there is no mounting misalignment in the shaft-end configuration, MAG becomes a constant value.

To account for the variation in mounting tolerances and ambient temperatures, it is recommended to install the sensor in a position where MAG is 50mT when there is no mounting misalignment.

Misalignment

Ideally, the centers of the magnet and the sensor should be aligned on the rotational axis in the shaft-end configuration. Misalignment is defined the distance from the sensor's center to the axis of rotation.

Diametral and Axial Magnets

There are two types of magnetization directions: diametral and axial.

A diametral magnet is magnetized across the circumference of the circular face of the magnet, as shown in the lower left figure. An axial magnet is magnetized in the direction perpendicular to the circular face of the magnet as shown in the lower right figure.

AKM's rotation angle sensor detects (transverse) magnetic fields that are oriented parallel to the chip surface.  Because of this, the rotation angle sensor is generally used with a diametral dipole magnet.

Diametral Magnet
Axial Magnet

Sintered Magnets

A sintered magnet is manufactured by pressing magnetic powders into a specific shape and then cured with intense heat. Sintered magnets typically include ferrite magnets, samarium cobalt magnets and neodymium magnets. These magnets can be found in standard shapes such as a cylinder and a rectangular solid.

Neodymium and Ferrite Magnets

Permanent magnets can largely be classified into two types of ferrite magnets : samarium cobalt (SmCo) and neodymium iron boron (NdFeB) . In Magnet Selection Guideline, sintered neodymium magnets and sintered ferrite magnets are introduced as magnets to be used in conjunction with the AK74xx series.

Ferrite magnets are characterized by low cost and high productivity. Neodymium magnets are more expensive than ferrite magnets, but they offer higher performance with a high residual magnetic flux density.