REED SWITCH TECHNOLOGYIntroduction
Purpose› Discover Standex Electronics’ Reed Switch TechnologyObjectives› Explain reed switch function and unique features› Explain the structure and manufacture of a reed switch› Explain some basic switch parameters› Describe reed switch applications and basic operation

What is a Reed Switch?

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Electromechanical switching device
Consists of two ferromagnetic reeds
Hermetically sealed glass envelope
Switching occurs when brought into amagnetic field generated by apermanent magnet or electromagnetic
coilRange in size from 0.025” to 2” longWhy is the Reed Switch unique?

UniqueCharacteristics

Very simple in its
structure

Hermetic seal allows
them to exist or
operate in almost
any environment

No wearing parts

Reliable switchingfor billions ofoperations

Draws no power in
the normally openstateReed Switch Structure
Glass Tube
› Temperature Coefficient of Expansion (TCE) of
glass exactly matches NiFe reeds› Hermetically sealed› Both ends of the glass tube are heated and theglass melts and forms the hermetic sealencompassing both ends.
› During the glass sealing process the glass cavity
is usually filled with an inert gas (typicallynitrogen) or the cavity may be evacuatedcreating a vacuum. This vacuum usually supports
high voltage switching (in excess of 1000 Volts).
› Nitrogen filled

Reed Switch Structure
Reed Contacts›
Nickel/Iron (NiFe) alloy›
Under layer of gold, copper or Tungsten 0.25µm to 0.5µm›
Outer layer rhodium, ruthenium or iridium 1.0µm to 2.0 µm

Basic Switch Parameters
Pull-In (PI) refers to the point where the reed switch
contacts close

Drop-out (DO) refers to the point where the reedswitch contacts openAmpere Turns (AT) or milliTesla (mT) define therelative magnetic strength or sensitivity of theopening and closing points

Basic SwitchParameters•

Hysteresis is the ratio of thedrop out and the pull in, and ismeasured as a percent (%) ordecimalStandex to OKI AT Conversion

Reed Switch Applications
Applications››

Switching, non-contact sensing, liquid level monitoring and counting› As a Reed Sensor or Level Sensor using the externally applied magnetic
field produced by a permanent magnet when brought into proximity tothe reed switch› As a Metal Detection Sensor by detecting a ferromagnetic sheet orplate› As a Reed Relay, the reed switch is activated when the electromagnet
coil is energized producing a magnetic field around the switch
Vehicles, safety engineering, household appliances, medical devices,
telecommunications and industrial systems

Reed Switch
Operation
As a Reed Sensor•••

Switch contacts willclose and remainclosed when a magnet
is brought into
proximity with a reedswitch
Contacts will reopenand remain open oncea magnet is distanced
from the switch

Reed Switch
Operation
As a Metal Detection ReedSensor••

Switch contacts will closeand remain closed whena ferromagnetic object is
moved into proximitywith metal detection
sensor (MK02 Seriespanel or PCB mount)
Contacts will reopen andremain open once
ferromagnetic material isdistanced from the MK02
sensorReedSwitchOperation
As a Reed Relay•••

Relay power OFF –Switch contacts
remain in normallyopen state and draw
no power
Relay power ON –Coil is energized andswitch contacts
close and remain so
until coil is turned off

Reed Switch Operation
Water Flow Sensor››››

Reed Switch is secured tostationary object
Permanent magnet rotates onmoving paddle
Rotation speed varies with filter
debris volume
Water flow is detected by paddle
speed signaling filter statusindicator lights

Click to Animate

Reed Switch Operation
Liquid Level Sensor› Floats have built-in ring magnet› Float magnet slides over switch withchange in fluid level causing reedswitch to activate› Reed switch activates LED indicator

Click to Animate

Applications
Test and measurement
Security and alarmHousehold appliances
Automotive
Medical devices
Telecommunication
Industrial applications

SummaryA Reed Switch is a small
electromechanical device having two
ferromagnetic reeds hermeticallysealed a glass envelope. Whenbrought into a magnetic field, thereeds will close, creating a switching
function.

They are very simple in structure
and are hermetically sealed so thatthey can be used in almost anyenvironment. Protect from theoutside environment, the contacts
are not susceptible to wear and will
typically perform billions of reliableoperations.

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