We’ve done a test of the reed contact on our SimplePack Plus. You can find information about the reed sensor we’re using here.
The purpose of this testing was to find out:
- Best magnet type to use
- Best magnet shape to use
- Best magnet strength to use
- The best way to place the magnet
Best magnet type to use
We have chosen the best permanent magnet type. Some use cases can be covered more efficiently with temporary magnets, but this implementation is rather advanced, so if you want to know more, write to us to email@example.com!
The magnet type to use is definitely Neodymium Iron Boron (NdFeB) as it is the strongest when it comes to power: size ratio. Even though NdFeB magnets are generally more fragile than other types of magnets, the accessibility (and lower cost) make them the ideal solution in case of mass deployments. The magnet type to choose is generally based upon your use case, but we went straight for the kill and chose NdFeB as the best type to use because most use cases that are covered by the reed sensor or a combination of the reed and other sensors in SimpleHw devices include monitoring door/rolldown/covers opening and closing.
If you have a different use case, please read this and decide what’s best for you.
Best magnet shape to use
As above, in general, the best magnet shape depends on the use case. And please note that not only the shape matters, but also the direction of the magnetization matters (which means that the two magnets of the same shape can have completely different induction lines and magnetic field form, more here.
You have to choose the magnet shape according to the desired functionality, but generally, we have found that block magnets generally perform the best. You can look at the comparison of the magnets we tested down below in the table.
Best magnet strength to use
This depends on whether you want the device to actually touch the magnet or for the device to come within close proximity to it. We recommend the second option which requires a stronger magnet but has less room for error. Feel free to check out the table below where you can find what magnet shape & strength activated the reed counter at what distance.
The data in the table in the magnet strength column is the pull strength of the magnet (the highest possible holding power measured in kilograms). It‘s the force required to pull the magnet away from a flat steel surface where the magnet and the surface have full surface-to-surface contact. The results are the distance from the reed sensor that activated it.
|Cylinder||Height 20 mm, diameter 10 mm||5 kg||8 mm|
|Cylinder||Height 40 mm, diameter 10 mm*||5 kg||19 mm|
|Cylinder||Height 40 mm, diameter 10 mm||10 kg||28 mm|
|Disc||Height 2 mm, diameter 25 mm||3,2 kg||3 mm|
|Disc||Height 10 mm, diameter 25 mm||8 kg||8 mm|
|Block||40 x 10 x 5 mm||7,5 kg||20 mm|
|Block||40 x 10 x 7 mm||9,2 kg||25 mm|
|Block||40 x 10 x 10 mm||15 kg||31 mm|
|Block||40 x 20 x 10 mm||20 kg||45 mm|
*this cylinder magnet was magnetized in a different direction than the one below it
Best way to place the magnet
This is a case by case matter. With the information above, you should have a better understanding of how to implement the device in order to properly fit your use case. You should consider what you want the device to report and based on that, find the best way to attach it where needed. Also, the direction of magnetization is an important thing to consider.
Want to know more about the testing we have done?
- Newsletter No 6. In testing, we believe.
- Heat testing in the oven
- Cold Testing in the freezer
- PoC testing. Real-life use case.
Simple Hardware Team