“Magnet interaction effects on reed switch operations can be understood by looking at the magnetic lines of flux and the way the magnet works.”
A surface mounted reed switch and magnet interaction shown in 3-D.
A reed switch is an electromagnetic switching device. Two ferromagnetic blades are housed in a hermetically sealed glass envelope. It has a very simple overall structure and a temperature coefficient of expansion of glass that exactly matches NiFe reeds. Reed switch operation happens when brought into proximity of a permanent magnet. The attractive polarity of the magnet magnetizes the reed contacts.
Magnet Interaction Effects
First, the magnet interaction effects the reed switch when a permanent magnet
(as shown below) is brought into the proximity of the switch. What happens is the individual reeds become magnetized with the attractive magnetic polarity as shown. Second, the external magnetic field’s strength or magnetic force of attraction causes the reed contact to close. Finally, since any residual magnetism on the reed blades would affect the opening and closing behavior. Therefore, the reed blades are annealed and processed removing any magnetic retention.
Invincible lines of flux cause the reed switch and magnet interaction.
Magnetic Lines of Flux
The magnetic lines of flux are the invisible energy forces created by the magnet that react to open and close the switch contacts. Once the magnet crosses the pull-in lines the contacts close. As long as the magnet stays within the pull-in boundary the contacts will remain closed. Similarly, when the magnet crosses the drop-out lines the contacts will open.
The Way the Magnet Works
A magnet interaction effects the reed switch contacts in a few different ways. The first way is positioning the magnet perpendicular to the reed switch. Then moving the magnet downward and back up so it will travel through the lines of flux. Consequently, the contacts will open and then close again. The next way of making the contacts react is by having the magnet parallel to the reed switch and moving it up and down or side to side depending on where it is parallel to the reed switch. In other words, up and down movement of the magnet parallel to the switch will open and close the contacts. Likewise, moving the magnet side-to-side on either side of the switch will also cause the contacts to open and close. The last way the magnet works is rotating it 90-degrees and centered over the center lobe of the reed switch. Many applications use this approach to count rotations of mechanisms, that in turn translate the rotations to specific functions.
Magnet interaction occurs by rotating the permanent magnet 90-degrees. The reed switch operates multiple times as a result of the change in polarity.
How a Reed Switch Operates Using a Magnet
Reed sensors control on and off function using a reed switch and a magnet. Examples of reed sensor applications range from control circuits and fluid level monitoring and detection in coffee pots to car parts. Without the magnet, reed switch’s would not operate, and without a moving mechanism to attach to, the magnet would not move through the reed switch’s sphere of influence, which is what causes the magnetic flux to interact with the sensitivity lobe arrays, which then creates the switching function.
A liquid level sensor application showing multiple reed switch and float detection points.
Reed switch sensor applications are increasing every day. Knowing the details behind how they work
can offer much insight into their proper operation. Understanding their influence with each other is key to a successful reed sensor application. The Standex team is standing by to fill the ever-changing needs of customers across industries, and across the world, through our Partner, Solve, Deliver®
approach. Get in touch with our team
to learn more about our carefully engineered solutions.
For a deeper understanding of how a reed switch works download our Reed Technology Databook.
This databook will provide a deep dive into what a reed switch is and how a reed switch works which includes extensive examples of various applications, features, and benefits.