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Magnet Information
In general, there are four families of magnets available commercially. Factors such as operating temperature, demagnetizing effects, field strength, environmental characteristics, and available space for movement etc. need to be considered before selecting a magnet for a reed switch or reed sensor application. An overview of each of the families of magnets is given below.
Highest energy product
Very high remanance and coercivity
Relatively low priced
Mechanically stronger than SmCo
Some grades can be used up to 230°C
Not recommended in Hydrogen atmosphere
Bonded types can be machined but not tapped
High energy product
Suitable for high performance applications
High resistance to demagnetization
Excellent thermal stability
High corrosion resistance
Most expensive magnet
Can be used up to 300°C
Prone to chipping - should not be used as a structure
Cheaper than rare earth magnets
Highest working temperature of 550°C
Lowest temperature coefficient
Low coercivity when compared to other types
High induction levels
Brittle
Poor thermal stability
Cheapest of all types
Can be used up to 300°C
Needs grinding to meet tight tolerances
High corrosion resistance
|
Cost |
Ferrite |
AlNiCo |
NdFeB |
SmCo |
|
Energy |
Ferrite |
AlNiCo |
SmCo |
NdFeB |
|
Operating Temperature |
NdFeB |
Ferrite |
SmCo |
AlNiCo |
|
Corrosion Resistance |
NdFeB |
SmCo |
AlNiCo |
Ferrite |
|
Resistance to Demagnetization |
AlNiCo |
Ferrite |
NdFeB |
SmCo |
|
Mechanical Strength |
Ferrite |
SmCo |
NdFeB |
AlNiCo |
|
Temperature Coefficient |
AlNiCo |
SmCo |
NdFeB |
Ferrite |
|
Property |
CGS Unit |
SI Unit |
Conversion Factor |
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Magnetic Flux |
Maxwell |
Weber |
1 Weber = 106 Lines |
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Flux Density (B) |
Gauss |
Tesla |
1 Tesla = 104 Gauss |
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Magnetomotive force |
Gilbert |
Ampere-turn (AT) |
1 Gilbert = 0.796 AT |
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Magnetizing force field (H) |
Oersted |
Ampere-turn / metre |
1 Oersted = 79.577 AT / m |
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