Magnetic encoder is widely used in applications requiring precise position(Relative or absolute value), speed, and direction sensing. They work by detecting changes in magnetic fields, typically generated by a magnet attached to a rotating or linear target. Below is an overview of the different types of magnetic encoder chips and different type of magnetic as moving part.
1. Types of Magnetic Encoder Chips
1.1 Hall Effect chips
Principle: Measure the voltage generated across a conductor when exposed to a magnetic field (Hall effect).
Applications: Rotary encoders, linear encoders, and motor control.
1.2 Magnetoresistance Effect chips
The magnetoresistance effect refers to the characteristic of a material’s resistance value changing when an external magnetic field is applied. The magnetoresistance effect is mainly divided into:TMR,AMR,GMR.
| Type | TMR | AMR | GMR |
| Full Name | Tunneling Magnetoresistance Sensor | Anisotropic Magnetoresistance Sensor | Giant Magnetoresistance Sensor |
| Operating Principle | Quantum tunneling effect (ferromagnetic/insulator/ferromagnetic sandwich structure) | Resistive anisotropy due to ferromagnetic material lattice orientation | Spin-dependent scattering (alternating magnetic/non-magnetic multilayer structure) |
| Sensitivity | Ultra-high (up to 10mV/V/Oe) | Moderate (~3mV/V/Oe) | High (~8mV/V/Oe) |
| Cost | High | Low | Medium |
| Key Features | Ultra-high sensitivity, nanoscale precision, low temperature drift, strong directional sensitivity | Cost-effective, wide temperature range, excellent linearity | Wide dynamic range, strong noise immunity, stable multilayer structure |
| Measurement Limit | Zero-field/ultra-weak field precision measurement | High-field/high-robustness environments | Wide-range/high-frequency dynamic fields |
| Failure Mode | Zero-field drift self-calibration | Stable saturation under overload | Automatic filtering of ultra-high-frequency signals |
| System Integration | Ideal for ultra-low-power implantable devices | Suitable for safety-critical systems | Compatible with high-speed digital interfaces |
The following is a comparison of the magnetic resistance ratios of three types of magnetoresistance effect:
2.Different type of magnetic rings as moving part for magnetic encoders
The magnetic ring material used for magnetic encoders can be magnetic materials such as ferrite, neodymium iron boron, samarium cobalt, etc.This type of magnetic ring can be divided into:
- Single pole magnetic ring
- Multi pole magnetic ring
- Multi pole dual code track magnetic ring
- Irregular magnetic ring
2.1 Single pole magnetic ring
A single pole magnet is a magnet with a pair of NS poles. The magnetic field generated by it only has one cycle.
2.2 Multi pole single track magnetic ring
The following figure shows the magnetic field distribution of a 128 pole planar magnetized magnetic ring, along with the magnetization principle diagram of the magnetic ring:
128 poles, then 64 pairs of NS poles, will produce 64 sine wave periods. In a rotary encoder, only relative angle changes can be obtained after one rotation. This type of magnetic encoder is mainly used as incremental encoders and cannot obtain absolute position data within one revolution.
In the appllication of motion control, in order to obtain the direction of rotation, a waveform with a phase difference of 90 degrees needs to be generated. Therefore, another Hall chip needs to be placed at the angle of 90 degrees.
2.3 Multi pole dual track magnetic ring
In order to measure the absolute position of a circle, a cursor scheme is needed. It can achieve higher resolution and also measuring absolute angles.
The cursor scheme uses two magnetic tracks for measurement, each consisting of multiple NS poles magnetized. The mystery lies in the number of NS pole pairs in the inner and outer circles.
If the outer ring is 32 pairs of magnetic poles and the inner ring is 31 pairs of magnetic poles, the magnetic induction intensity difference between the inner and outer rings is different. This difference makes it as the data source of absolute position.
2.4 Irregular magnetic ring
In some typical applications, a customized magnetization is needed in order to achieve higher performance.
3. OBT multi pole magnetic ring products
OBT Rubber Seal specializes in providing customized multi-pole magnetic rings which could work with a wide range of motion control systems. These multi-pole magnetic rings are produced as combination of ferromagnetic rubber and metal.
If you are interested in our multi-pole magnetic ring products, please contact us for more information and quotation.
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