REED SWITCH BASICS PART I

Introduction
Table of Contents› What is a Reed Switch?
› Reed Switch Basic Structure› Reed Switch Lead Material - Ruthenium› Reed Switch Lead Material – Iridium› AT Ranges› Basic ParametersWhat is a Reed Switch?

›A Reed Switch is a small
electromechanical device having
two ferromagnetic reeds
hermetically sealed in a glass
envelope, and when brought intoa magnetic field the reeds willclose, creating a switching
function. They range in lengthfrom 2.0 inches long to as small as0.025 inches long.

Reed Switch Basic Structure

››

›

›

Materials
The two reed leads are made up ofNickel/Iron (NiFe) alloy (52% nickel).
To be affected by a magnetic field thereed leads must be ferromagnetic.
The three most popular materials innature and easy to anneal are
ferromagnetic: iron, cobalt, and nickel.

Reed Switch Basic Structure›››

Materials
The tips of the two reeds are either
plated or sputtered with rhodium,ruthenium or iridium, with an underlayer of either gold, copper or Tungsten
The under layer is usually 0.25µm to0.5µm with the outer layer usually
1.0µm to 2.0 µm

Reed Switch Lead Material – Ruthenium/Iridium››››

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

Reed Switch Basic Structure
Materials›››

A Glass tube is used for the outer packaging whose
Temperature Coefficient of Expansion (TCE) exactly
matches the NiFe alloy.
Both ends of the glass tube are heated and the glass
melts and forms the hermetic seal encompassing bothends.
During the glass sealing process the glass cavity is usually
filled with an inert gas (typically nitrogen) or the cavity
may be evacuated creating a vacuum. This vacuum
usually supports high voltage switching (in excess of 1000Volts).

AT Ranges››

An AT range essentially groups several ATs together
forming an AT range
The first row shows a 10 AT to 21 AT range

10111213

1415

101112131415

1011121617181920

21This represents a 10 to 15 AT range

This is a 10 to 12 AT range.

Could this be shipped to a customer as a 10 AT to 15 AT range ?

101112131415161718192021

Basic Switch Parameters›››

Most companies measure the Reed Switches in Ampere Turns(AT). Universally milliTesla (mT) is a more generally acceptedmagnetic measurement unit. MEDER is the first and only one toconvert over to mT, but continues to reference AT.
Pull-in and Drop-out are the points referred to when the contacts
close and open. AT or mT indicate the relative magnetic strength
at these opening and closing points. Also, its very convenient tospecify the closure and opening points in distance for specificapplications.
Hysteresis is another parameter that is useful particularly tomeasure liquid levels. Its simply the ratio of the drop out and thepull in, and is measured as a percent (%) or decimal.

Standex To OKI AT Conversion

Ampere-Turns (AT)›››Near term and long term we are converting over tomilliTesla. This will be very helpful for our customers,
but will not eliminate the issues described above.
If all reed switch suppliers converted to milliTesla, itwould make things much simpler.
milliTesla is the universal standard throughout theworld; therefore, unifying the magnetic
measurement system

Reed Switch Basics Part I - END
Content of part II:› How does a Reed Switch/Sensor work?
› What are a Reed Switch‘s parameters?

FOR MORE INFORMATION ON OUR CAPABILITIES,AND HOW WE CAN PARTNER, SOLVE, AND DELIVER®
TO YOUR NEEDS, PLEASE VISIT US AT
STANDEXELECTRONICS.COM