Selection of Permanent Magnet Materials and Application of Magnetic Reed Sensors

Selection of Permanent Magnet Material for Magnetic Reed Sensor

Generally speaking, the selection of magnet for magnetic reed switch sensor needs to consider different application factors, such as working temperature, demagnetization effect, magnetic field strength, environmental characteristics, movement and application. The main features for the most popular types of hard magnetic materials as follows:

Rare Earth Neodymium-Iron-Boron Magnet

1. Highest energy product

2. Very high remanance and coercivity

3. Relatively low price

4. Better mechanical strength than magnet Samarium Cobalt

Rare Earth Samarium Cobalt Magnet

1. High magnetic energy product

2. Suitable for high performance applications

3. High demagnetization resistance

4. Excellent thermal stability

5. High corrosion resistance

6. The most expensive magnet

7. Used in temperature up to 350 ° C 

Alnico Magnet

1. Cheaper than rare earth magnets

2. Maximum operating temperature to 550 ℃

3. Minimum temperature coefficient

3. Low coercivity

4. High residual induction

Ferrite or Ceramic Magnet 

1. Brittle

2. Cheapest among those four magnet materials

3. Working within 300 ° C

4. Grinding required to meet strict tolerances

5. High corrosion resistance

Main Applications of Magnetic Switch Sensor

1. The speed sensor on the bicycle is used with cylindrical Neodymium magnet.

2. Magnetic reed switch is unique in fluid transmission system. The magnetic switch can be directly installed on the cylinder block. When the piston with the SmCo magnet ring moves to the position of the magnetic switch, the two metal reeds in the magnetic switch are pulled in under the action of the magnetic field of the magnetic ring to send a signal. When the piston moves away, the tongue spring switch leaves the magnetic field, the contact automatically opens and the signal is cut off. In this way, the position of cylinder piston can be detected conveniently.

3. Another kind of magnetic reed switch is the new magnetic proximity switch, magnetic switch sensor, also known as magnetic induction switch. It has a plastic shell, which encapsulates the reed switch in the black shell and leads out the wire. The other half of the plastic shell with a NdFeB hard magnet is fixed at the other end. When the hard magnet is close to the switch with wire, it sends out the switch signal. The general signal distance is 10mm. This product is widely used in anti-theft doors, household doors, printers, fax machines, telephones, and other electronic instruments and equipment.

4. The refrigerator door uses a reed switch for door closing detection. The permanent magnet is mounted on the door and the magnetic reed sensor is connected to a fixed frame hidden behind the outer wall of the refrigerator. When the door is opened, the reed sensor cannot detect the magnetic field, causing the LED bulb to light up. When the door is closed, the magnetic sensor detects the appropriate magnetic field and the LED goes out. In this application, the microcontroller in the device obtains a signal from the reed sensor, and then the control unit activates or deactivates the LED.