Members' Profiles

Oki Sensor Device
CorporationPerhaps you are familiar with the reed switch. So
named because its electrodes resemble the stems of a reed,a reed switch has a very simple construction with two or
three reed electrodes sealed in a small glass tube (Fig. 1).
OFFreedContact point

Takao Yano
Inert gas

Managing Advicer

Glass tube

ONNN

SSS

The reed switch is also used in the float sensor todetect fluid levels. In combination with a magnet, thisswitch has many other applications, as well. In particular,
the float switch is indispensable for detecting the flowrate of gas and water, and in automotive applications that
require high reliability.
Another method frequently used for operating thereed switch consists of winding a coil around the switch
and applying a current to the coil to generate a magnetic
field. A reed switch wrapped by a coil and covered with aprotective resin or the like is called a reed relay.
A major application for reed switches is an IC tester. In
addition to their reliability-they can endure hundreds ofmillions of on/off operations-the reed switch is used for its
good high-frequency property. The reed switch was
initially developed for use in a crossbar telephoneswitchboard. Later the diameter of the switch was reduced
from its initial 30 mm or more to its current minimum of 7
mm to be provided in keyboards and the like.
In recent years, however, electronic equipment has
been developed with more functions and an increased
number of mounted parts, as represented by the cellular
phone. Hence, there has been much demand to makeeach part lighter and more compact.
Similarly, there have been numerous calls to improvethe efficiency of accommodating parts in industrial
equipment and automobiles, in order to mount a large
number of parts in a smaller space. At present it isbelieved theoretically that the reed switch can be
reduced to a minimum of 5 mm in diameter.
Today, reed relays utilizing micromachine technology(MMR: micromachined relays) are being developed. Ourcompany is also developing reed switches using
micromachine technology as a core product for theensuing period.
By taking advantage of the feature of reed switches(the open and closing of contact points throughmagnetism), we can provide more compact microsize
reed switches with high integration. It is our hope that
we can fill the needs of a wide-range of users by
producing reed switches, not just for current
applications, but also for markets that cannot yet utilize
reed switches; and to uncover and create new
applications.

NFig. 1 Operating principles of the reed switch

Unfortunately, the reed switch is not widely known
because people are not exposed to it much. However, byencapsulating the electrode contacts in a glass tube andfilling the tube with inert gas, the electrodes are notgreatly affected by external factors, such as temperatureand humidity and corrosive gases. This feature allows thereed switch to be used in various fields.
Since the reed switch is turned on and off only by
variations in a magnetic field applied externally, theswitch does not require power necessary for turning otherswitches on and off. All that is required is the reed switch
and a magnet. When a magnetic field is brought near thereed switch, an induction field is generated around thereed electrodes, which are formed of a ferromagnetic
material. As a result, the contact points on the twoelectrodes are magnetized as a north pole and a southpole and contact each other through mutual attraction.
A reed switch can be used, for example, to detect theopening and closing of a door, such as the door of a houseor a refrigerator, by mounting a magnet on the door ordoor frame and a reed switch on the other. When the door
is closed, bringing the magnet close to the reed switch, thecontacts in the reed switch meet and close the circuit.

Float

Reed switch

MagnetFig. 2 Float sensor

7