HSI Sensing Magnet Application Notes

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Magnets and ActuatorsApplication Notes


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Table of Contents

Magnet and Actuator Basics-Environmental Considerationspage 1

Magnet and Actuator Operationpage 3

Magnet and Actuator Handlingpage 7


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Magnet and Actuator Basics - Environmental Considerations

What is a magnet, and what is an actuator?

For our purposes, the most notable property o a magnet is that it generates a magnetic eld thatoperates a reed switch or proximity sensor.

An actuator is simply a magnet placed in a housing. Customers oten pair our actuators with ourproximity sensors or a magnetic sensor package. Also, many o the actuator housings provide a wayto mount the magnet onto a surace and provide environmental protection.

Basic Types

The three basics types o magnets that HSI Sensing typically uses in applications are Alnico, Ceramicand Neodymium. Each has diferent qualities and may be impacted by their surroundings.

Alnico

Alnico rod and bar magnets have high residual induction and energy product comparedwith ceramic magnets, and low coercive orce compared with ceramic and rare earthmaterials (more subject to demagnetization).

Temperature stability in high temperature applications, and a maximum workingtemperature o approximately 1000F (540C).

Ceramic

Low cost and good holding strength, block magnets ofer economical magnet power orprice-sensitive applications.

Ceramic block magnets are charcoal grey in color, and do not appear metallic. Ceramic magnets are not suited or high temperature applications (over 250 C).

Neodymium

Neodymium magnets are the most powerul commercially produced magnets. Neodymium magnets are hard and brittle and may chip or break i dropped. Neodymium disc magnets are magnetized through the thickness.

Neodymium magnets are oten assembled into products using strong adhesives such asLoctite 325. Make sure that all contact suraces are clean and dry prior to bonding.

Please use caution when handling magnetized neodymium magnets. Their exceptionalmagnetic orce may cause them to attract to metal (or to each other) sostrongly that ngers in their path could be pinched or injured.


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Magnetic Interference

In proximity sensor applications, the magnet or actuator is intended to be the singlesource o magnetic eld or operation. Countereit sources o magnetism can causeerroneous operation.

Sources o magnetic intererence: Nearby components containing iron or magnetized parts, including brackets, bolts,

washers, screws, nails, base metal, and the like. Electronic components manuactured with errous materials can generate magneticelds or become magnetized when exposed to magnetism. Such components includebut but are not limited to capacitors, batteries, motors, wire, and transormers.

Any o these components can reshape or even signicantly weaken the magnetic eld whenthey are close to the magnet. Non-errous mounting hardware is recommended.

Consider the chemical resistivity o your magnet and/or actuator housing based on yourapplications environment.


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Magnet and Actuator Operation

With a Reed Switch

With a Magnet

A reed switch is activated by a magnetic eld. Its important to realize that there are numerouspossibilities or orientation o a switch within a given magnetic eld. The diagrams on the nextpage show several basic examples o reed switch operation with the use o a moving and stationarymagnet.

The length o the magnet and the length o the reed switch both afect the magnetic eld coupling.

The physical parameters o a magnetsuch as length, width, thickness or diameterimpact the sizeand shape o the resultant magnetic eld. For example, an M-01 (.062 h/w x .50 length Alnico) mustbe very close to a reed switch to ensure operation, while an M-15 (.250 dia. x 2.25 length, Alnico) willoperate a reed switch at a much greater distance.


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With a Proximity Sensor

For proper alignment, position and location, please reer to the product specication sheet. Anexample is provided below.

Please note that a shorter magnet or actuator has a shorter eld, and a longer magnet or actuatorhas longer eld.


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FIGURE 1

FIGURE 2

CORRECT CORRECT

FIGURE 3

FIGURE 4

INCORRECT INCORRECT

CLUSTERED MAGNETS

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Magnet and Actuator Handling

Disengaging Magnetized Magnets

Individual magnets must be pulled rom the row horizontally. See images below. Do not slide magnets against each other Do not allow magnets to cluster

Connecting Magnetized Magnets

Group magnets that are magnetized, allowing the magnetic elds to attract rom end to end(orming a row). See Figures 1, 2, 3 and 4.

Do not allow magnets to cluster.


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3100 NORGE ROAD, CHICKASHA, OKLAHOMA 73018 | PHONE 405.224.4046 | FAX 405.224.9423 | HSISENSING.COM

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HSI Sensing Magnet Application Notes