Windings for magnetic latching reed relay

A magnetic latching relay includes three control windings disposed about an encapsulated reed switch having a pair of reeds constructed of a remanent magnetic material. A first winding is disposed about one reed and second and third windings are disposed about the other reed. The windings are arranged so that a current pulse applied to the first and second winding generates magnetic flux fields in the same direction that produce magnetic poles of opposite polarity at the contacting ends of the reeds and causes the contacting ends to close while a current pulse applied to the first and third windings generates magnetic flux fields in the opposite direction that in turn produces magnetic poles of like polarity at the contacting ends and causes the contacting ends to open.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to electromagnetic switching devices and 
particularly to an improved magnetic latching reed relay. 
2. Description of the Prior Art 
One type of a magnetic latching read relay includes a pair of reeds made 
from a magnetic material which, when exposed to a magnetic flux, will 
assume a magnetic state and remain in that state until exposed to a 
magnetic flux of opposite direction. The ends of the reeds overlap to 
function as a pair of normally open contacts. An example of such a relay 
is taught by U.S. Pat. No. 3,059,075 issued to R. L. Peek on Oct. 16, 
1962. 
Various arrangements of control windings have been employed with 
magnetically latched reed relays. One such arrangement is taught by U.S. 
Pat. No. 3,037,085 issued to T. N. Lowry on May 29, 1962. That arrangment 
employs the principle of differential excitation and employs two pairs of 
windings connected so that the relay is released, i.e., the contact pair 
is opened, by applying a current pulse to one pair of windings and the 
relay is operated, i.e., the contact pair is closed, by concurrently 
applying pulses of the same polarity to both pairs of windings. 
Another control winding arrangement taught by U.S. Pat. No. 3,793,601 
issued to R. J. Anger et al. on Feb. 19, 1974 operates or releases the 
reeds with a single pulse. Each of a pair of identical release windings is 
arranged over a corresponding one of a pair of reeds. The release windings 
are series connected so that a single pulse applied to the windings causes 
a magnetic field of one direction to be produced around one reed and a 
magnetic field of an opposite direction to be produced around the other 
reed. The resultant magnetic flux is such that the contact ends of the 
reeds are of the same magnetic polarity and thus separate. An operate 
winding in association with one of the two release windings is wound in a 
manner to produce a magnetic flux magnitude greater than the magnitude 
magnetic flux generated by the associated release winding and having a 
flux direction opposite to the flux direction produced by the associated 
release winding. The operate winding is series connected to the associated 
release winding so that a single current pulse flowing through the operate 
and the pair of release windings causes the contact ends of the reeds to 
have magnetic states of opposite polarity with the result that the contact 
ends of the reeds attract whereby the contact pair is closed. 
The arrangement taught by the Anger patent has an inefficiency in its 
operation to close the reed contacts in that the operate winding must 
generate a magnetic field of sufficient strength to overcome the magnetic 
field concurrently produced by one of the release windings. 
SUMMARY OF THE INVENTION 
A preferred embodiment of the present magnetic latching reed relay has 
three windings. In accordance with the principles of this invention a 
first or common winding is positioned over one of a pair of reeds 
constructed of a remanent magnetic material; an operate winding and a 
release winding are located over the other reed. The operate winding is 
serially connected with the common winding in a manner that a current 
pulse flowing through the common and operate windings causes magnetic 
fields to be produced around both reeds in the same direction. The 
resultant magnetic flux is such that the free ends of the reeds have 
opposite magnetic polarity and thus attract thereby closing an electrical 
path. The release winding is serially connected with the common winding in 
a manner that a current pulse flowing through the common winding and the 
release winding causes a magnetic flux field of one direction to be 
produced around one reed and a magnetic flux field of an opposite 
direction to be produced around the other reed. The magnitude of the flux 
produced by the release winding is greater than the magnitude of the flux 
produced by the operate winding and has a flux direction opposite to the 
flux direction produced by the operate winding. A current pulse flowing 
through the common and release windings produces a resultant magnetic flux 
such that the free ends of the reeds have the same magnetic polarity and 
thus repel each other whereby the electrical path is opened.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The read relay illustrated in FIG. 1 includes a reed switch shown generally 
at 102 which comprises a pair of reeds 106 and 108 sealed in a glass 
envelope 103. The free ends of the reeds 106 and 108 overlap and are 
coated with a highly conductive material to form contacts 120. Each of the 
reeds 106 and 108 is constructed of a remanent magnetic material 
exhibiting a plurality of stable magnetic states and which retains its 
last-set magnetic state. These magnetic states are established exclusively 
by three control windings 112, 114 and 116. A first or common winding 112 
is positioned over one reed 106. The second or operate winding 114 and the 
third or release winding are positioned over the other reed 108. 
The common winding 112 is wound in what is assumed to be clockwise 
direction from the terminal 132 to the common terminal 134. The operate 
winding 114 is wound in the same direction from the common terminal 134 to 
the terminal 136. The release winding is wound in the same direction from 
the terminal 138 to the terminal 135 which is in turn connected to the 
common terminal 134. The windings are wound so that the common and operate 
windings 112 and 114 each have m turns of wire and the release winding 116 
has n turns of wire, where n is greater than m. In the illustrative 
embodiment of the invention, the common and operate windings 112 and 114 
each have 45 turns of 34 gauge insulated copper wire and the release 
winding 116 has 68 turns of 34 gauge insulated copper wire. As is clearly 
illustrated in FIG. 2, the common winding 112 is serially connected to 
both the operate and release windings 114 and 116 so that a series 
electrical path may be established through the common and operate windings 
112 and 114 or through the common and release windings 112 and 116. The 
windings are connected so that the common winding 112 and the operate 
winding 114 are of the same magnetic sense and the release winding 116 is 
of the opposite magnetic sense. The magnetic sense of each winding is 
indicated in FIG. 2 and FIG. 3 by means of a dot. 
With reference now to FIG. 2, the magnetic fields produced during the 
operation of the relay will be described. A current pulse source 140 is 
connected to the terminal 132 and a ground 142 is connected to the 
terminal 136 so that a current pulse generated by the pulse source 140 
flows from left to right through the series combination of the common and 
operate windings 112 and 114. The current flow through the common winding 
112 produces a flux field of a first magnitude about the reed 106 having a 
first magnetic direction indicated by the arrow 170 thereby creating 
magnetic poles N and S on the reed 106 as shown. The current flow through 
the operate winding 114 produces a flux field about the reed 108 also 
having the first magnetic direction as indicated by the arrow 172 thereby 
creating magnetic poles N and S on the reed 108 as shown. The flux field 
produces about the reed 108 is approximately equal in magnitude to the 
flux field produced about the reed 108. The free ends of the reeds 106 and 
108 are of opposite magnetic polarity and therefore attract each other 
with the result that the contacts 120 close. As stated hereinabove, the 
reeds 106 and 108 are of a remanent magnetic material that retains its 
last-set magnetic state. Therefore, at the termination of the current 
pulse, the reeds 106 and 108 will retain their respective magnetic 
orientations and the contacts 120 will remain closed. 
With reference to FIG. 3 the magnetic fields produced for releasing the 
relay, i.e., opening the contacts will be described. The current pulse 
source 140 remains connected to the terminal 132. The ground 142 is now 
connected to the terminal 138 so that a current pulse generated by the 
current pulse source 140 flows from left to right through the series 
combination of the common and release windings 112 and 116. The current 
flow through the common winding 112 produces a flux field of a first 
magnitude and having a magnetic direction as illustrated by the arrow 170 
thereby creating magnetic poles N and S on the reed 106 as shown. The 
current flow through the release winding 116 produces a flux field of a 
second magnetic direction as illustrated by the arrow 174. The magnetic 
flux field produced by the release winding 116 is opposite in magnetic 
direction to and greater in magnitude than the magnetic flux field 
produced by the operate winding 114 during relay operation so that the 
remanent magnetism of the reed 108 as a result of the relay operation, is 
overcome and the reed 108 will assume a remanent magnetic orientation in 
the opposite direction. The magnetic flux field produced by the release 
winding 116 is also greater in magnitude and of opposite magnetic than the 
magnetic flux field produced by the common winding 112. As a result, the 
magnetic flux field of the release winding 116 overpowers the magnetic 
flux field of the operate winding so that the south magnetic pole S that 
it produces is displaced to the left of the midpoint of the reed switch. 
Under the conditions described above, the reeds 106 and 108 repel each 
other thereby causing the contacts 120 to open or separate. At the 
termination of the current pulse the fields generated by the windings 112 
and 116 collapse and the reeds retain the magnetic orientation illustrated 
in FIG. 3 and the contacts 120 remain open. 
In the illustrative embodiment of this invention the current pulses for 
both operation and release of the relay are 2.5 .+-. 0.5 amperes for a 
duration of 1.44 milliseconds. 
It is to be understood that the above-described arrangement is illustrative 
of the principles of this invention. Numerous other arrangements may be 
devised by those skilled in the art without departing from the spirit and 
scope of the invention.