US3215795A

US3215795A - Reed switch control

Info

Publication number: US3215795A
Application number: US249185A
Authority: US
Inventors: Lynn H Matthias
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1963-01-03
Filing date: 1963-01-03
Publication date: 1965-11-02
Anticipated expiration: 1982-11-02

Description

Nov. 2, 1965 I H. MATTHIAS 3,215,795

REED SWITCH CONTROL Filed Jan. 3, 1963 2 Sheets-Sheet 1 NI COIL l2 H INVENTOR LYNN H. MATTHIAS ATTORNEY Nov. 2, 1965 H. MATTHlAS 3,215,795

REED SWITCH CONTROL Filed Jan. 3, 19 3 2 Sheets-Sheet 2 INVENTOR LYNN H. MATTHIAS New ATTORNEY United States Patent 3,215,795 REED SWITCH CONTROL Lynn H. Matthias, Fox Point, Wis., assignor to Allen- Brarlley Company, Milwaukee, Wis., a corporation of Wisconsin Filed Jan. 3, 1963, Ser. No. 249,185 3 Claims. (Cl. 20087) This invention relates to reed switch controls and it more specifically resides in a reed switch having two magnetic reeds with relatively movable contact ends, a magnetic member disposed adjacent the contact ends to modify magnetic field patterns associated with the reeds, and operating coils located on both sides of the magnetic member which function to close the reed contacts when both coils are energized.

Reed switches comprise a pair of thin, magnetic reeds within a glass envelope. At least one of the reeds is deflectable, and the ends of the reeds overlap slightly to function as switch contacts that move between open and closed positions in response to associated operating coils or other energizing means. These switches are particularly useful in circuits utilizing numerous switching elements that must operate with a very high degree of reliability over an extended time, and they are characterized by a rapid switching operation that makes them ideal for computer devices, logic circuits and telephone circuits.

In a host of reed switch applications the switch is combined with a pair of operating coils, and the reed contacts are to close only when simultaneous independent signals are transmitted to such associated coils. Cross-point switching is a typical application of this nature. In some other applications the reed switch must also return its contacts to open position upon discontinuance of either of the signals. It then functions as an and logic circuit element for both energization and deenergization of the operating coils.

In usual construction employing a pair of operating coils, each coil encircles one of the reeds and when it is energized by a current of prescribed value it develops a magnetic flux insuflicient to close the switch. However, upon energization of both coils the resultant fiux in the vicinity of the reed contact ends closes the switch, and in the instance of an an type switch deenergization of a single coil will cause the switch to reopen. Such a device may have limited magnetic tolerances for proper operation, with the result that either excessive or deficient amounts of flux may be developed if any construction or operating parameter is altered to any considerable degree. For example, when the magnetizing force of each individual coil is small enough to be below the drop out (switch opening) value, the combined magnetizing forces obtained upon simultaneous energization of the coils may not be much greater than the minimum at which switch closing will occur. In such switches a decrease in the applied voltages may result in the switch not closing when both coils are energized, and also the switch may remain closed when one coil is de-energized if the operating voltage is slightly increased. Also, if there is a small dilference between the magnetizing force required to pick up the switch and the magnetizing force required to drop out the switch, then a relatively small increase in voltage applied to a single coil may cause switch closure. Thus, some reed switch controls have serious disadvantages.

The present invention comprises a control for a reed switch having a main operating coil for each reed in combination with a magnetic member disposed in the immediate vicinity of the reed contact ends at a position between the coils. This magnetic member modifies the magnetic field in the vicinity of the contact ends to insure retention of the reeds in their initial open position upon Patented Nov. 2, 1965 energization of only one of the main operating coils. This retention is maintained for large values of magnetizing ampere turns being applied through the single coil, so that applied voltages can increase without affecting the characteristic of retaining the switch open until signals are applied to both coils. Thus, only upon energization of both coils will the reed contacts be actuated to closed position. The presence of the magnetic member also improves switch opening characteristics, in that the applied voltage to the coils does not have to be as critically controlled in order to have switch opening occur when one coil is de energized. To further enhance a rapid, positive reopening of the reed contacts a supplementary reverse coil may be used with each main coil to reduce the magnetic potential between the reed contacts upon deenergization of either main coil. Then, extreme reliability is obtained for operation as anand logic circuit element.

It is an object of this invention to provine a reed switch control which will operate over a large range of line voltages without impairing the operating characteristics of the switch assembly.

It is another object of this invention to provide a reed switch assembly in which magnetic interaction between closely adjacent switches is reduced to levels wherein adjacent switches do not influence one another, so that a compact assembly of a plurality of reed switches may be obtained.

It is another object of this invention to provide a reed switch control which is characterized by reliable operation, and which is not handicapped by severely critical switch response characteristics.

I It is another object of this invention to provide a reed switch control that may be readily manufactured in large numbers with substantial manufacturing tolerances.

The foregoing and other objects and advantages of this invention will appear from the description to follow. In the description reference is made to the accompanying drawings which form'a part hereof, and in which there are shown by way of illustration, and not of limitation, specific embodiments in which the invention may reside. For a determination of the scope of the invention, as distinguished from the specificness of the embodiments illustrated, reference is made to the claims appended hereto.

In the drawings:

FIG. 1 is a view of a reed switch control embodying the invention with a magnetic flux diverting plate broken away and in section and with operating coils depicted schematically,

FIG. 2 is a graph of characteristics of the reed-switch of FIG. 1,

FIG. 3 is a view of a reed switch like that in FIG. 1 modified by the addition of permanently magnetized latching magnets,

FIG. 4 is a view of another reed switch control embodying the invention, and

FIG. 5 is a side view, with parts in section, of an assembly of a number of reed switch controls of the invention.

Referring now to the drawings, there is shown in FIG. 1 a sealed, glass envelope 1 preferably filled with an inert gas. A pair of long,

thin reeds

2 and 3 extend into the interior of the envelope 1 from its

opposite ends

4 and 5. The

reeds

2, 3 are of a magnetic material that has suflicient flexnre to provide for movement of the inner ends 6, 7 at the center of the envelope 1. The inner ends 6, 7 are normally open and they overlap slightly to present facing contact surfaces that will move into engagement with one another in response to magnetic forces established by associated coils. The

reeds

2 and 3 also have suflicient conducting qualities to form satisfactory switch elements for an electric circuit, and thin external ends 8 and 9 function as terminals for connection into such a circuit. In the usual manufacture of these devices, the

reeds

2, 3 have a diffused gold coating that insures long and stable electrical life, and by providing an inert gas filled envelope 1, contact failure due to dust, dirt or atmospheric contamination is virtually eliminated. The glass envelope 1 with its

reeds

2, 3 comprises what is known as a reed switch, and, as stated, is useful in telephone circuits, computer elements such as decoders and shift registers, and similar apparatus where reliable high speed switching is essential.

The glass envelope 1 extends through a close fitting opening of a magnetic plate 11 that is centered with respect to the contact ends 6 and 7. A first operating coil 12 encircles the left hand end of the envelope 1, as viewed in FIG. 1, and its ends are joined to a pair of

terminals

13 and 14. A second operating coil 15 encircles the right hand end of the envelope 1 and has one end 'joined to the common terminal 13 while its other end extends to a terminal 16. Thus, the two

coils

12, 15 can be independently energized, and if desired they can have entirely separate terminals instead of a common connection such as the terminal 13.

In the operation of the device of FIG. 1, the presence 'of the magnetic plate 11 provides a mode of operation distinctly diiferent from that heretofore had in the absence of such member. If either

coil

12 or 15 is energized, without any energization of the other, the contact ends 6, 7 will remain open, and this open condition will persist for large values of ampere-turns well above normal operating values. By proper proportioning of the magnetic plate 11 the range may extend to current values causing a destruction of the coil, so that switch closure is definitely precluded. As a consequence an unwanted closing of the contact ends 6, 7 will not occur upon energization of but a

single coil

12, or 15, and fluctuations in operating voltage will not alter this switching characteristic. The plate 11 influences the pattern of the magnetic field in the vicinity of the contact ends 6, 7 to maintain a low value of flux density between the reed ends 6, 7 that is insufficient to develop a closing force between the reeds.

For the condition of a single energized coil, for example coil 12, a substantial amount of the magnetic flux in the right hand end of the associated reed 2 will be shunted off toward the plate 11 to inhibit the passage of any critically suificient amount of flux from reed end 6 to reed end 7 that would close the contacts. Flux shunted to, or diverted by, the plate 11 will pass from the plate 11 about the outside of the coil 12 to link therewith, and since it is primarily an air flux that does not give rise to a closing force for the contact ends 6, 7 it can be termed a leakage flux.

The

coils

12 and 15 are connected to have their respective magnetic flux components in the

reeds

2, 3 add to one another. Thus, for conventional symbolic representation applied to FIG. 1, when a positive voltage signal is simultaneously applied to the

terminals

14 and 16 the magnetic flux through the center of each

coil

12, 15 will be from the right to the left, and the cumulative eifects at the reed contacts 6, 7 will produce a sufficient magnetic intensity across the open contact gap to move the contact ends into closed position. Thus, switch closure is only established by simultaneous coil energization, and by virtue of the flux diverting plate 11, the unique switch characteristic shown in FIG. 2 is obtained.

In FIG. 2 the abscissa of the graph represents ampereturns for the coil 12 and the ordinate represents ampereturns for the coil 15. The curve 17 is a plot of limiting values of ampere-turns for the two

coils

12, 15 for which switch closure is obtained, and this curve is substantially asymptotic so that there is some threshold value of ampere-turns for each coil that is required for switch closure, even though a very high value of ampere-turns is applied through the other coil. This threshold value is represented by the letter m in FIG. 2. If the two

coils

12, 15 are operated with equal ampere-turns switch operation will be along the line 18, and the point 19 is the minimum value of equal ampere-turns at which switch closure occurs. It is advantageous to have a locus for the point 19 that requires only small ampere-turn values for the two coils, and by proper dimensioning of the diverter plate 11 and positioning of the

coils

12, 15 the coordinates x and y for the point 19 can each be brought within two times the necessary minimum ampere-turns m required for either coil for switch closure.

The arrangement of FIG. 1 can be modified by the inclusion of latching magnets at each side of the diverter plate 11, as shown in FIG. 3, where a set of four small permanent magnets 20 are disposed and oriented to develop a small biasing flux that passes through the

reeds

2, 3 in the same direction as that developed by the

coils

12, 15. (Like reference numerals have been applied in FIG. 3 for parts that correspond with parts in FIG. 1.) By this arrangement the

reeds

2, 3 can be closed by applying simultaneous signal pulses to the

coils

12, 15 and the latching magnets 20 will then hold the reeds closed. To open the reeds a reverse clearing pulse can be applied to either

coil

12 or 15. The magnetic flux at the reed contact ends due to the permanent magnets 20 may be of such a value that the switch can be closed by applying a large number of ampere-turns through a single coil. However, the ampere-turns that would be required may greatly eX- ceed the ampere-turns required per coil when closing by simultaneous energization of both coils with equal ampore-turns for each. In actual practice, the ratio of the ampere-turns required for switch closure by a single coil to the ampere-turns per coil when closed by simultaneous energization has been as great as 4:1 and more. These results have been obtained for a reed switch 0.2 inch in diameter and with a magnetic flux diverting member A inch thick.

Referring now to FIG. 4, there is shown a reed relay comprised of a glass envelope 1 and

reeds

2 and 3. (Like reference numerals have again been applied to parts like those shown in FIG. 1.) Associated with this relay is a magnetic flux diverting plate 11 and a group of operating coils which differ from those in FIG. 1 by the inclusion of supplementary coils that are connected to have reverse turns for establishing magnetic flux components in opposition that-of the main coils. Thus, there is a first coil set comprising a main operating coil 21 encircling the left hand side of the envelope 1 and a supplementary coil 22 on the opposite side of the diverting plate 11 that encircles the right hand side of the envelope 1. One end of the main coil 21 is connected to a common terminal 23, shown as a negative terminal, and the opposite end of the main coil 21 is connected through a lead 24 to the supplementary coil 22 in a manner to have the respective coil windings in opposition to one another. The supplementary coil 22 has fewer turns than the main coil 21, and upon energization the magnetic fields due to the common current flowing in the two

coil sections

21, 22 will be in opposition to one another, with the field of the larger coil 21 being the larger. But, similarly as for the device of FIG. 1, the reed switch will remain open even though large currents be caused to flow through the first coil set, so that a characteristic curve is obtained which is similar to that in FIG. 2.

A second coil set comprises a main operating coil 25 encircling the right hand side of the envelope 1 and a second supplementary coil 26 on the opposite side of the magnetic plate 11. A lead 27 extends from one end of the coil 25 to a common connection with the coil 21, and another lead 28 joins the opposite end of the coil 25 with the supplementary coil 26. The winding relation between the second main coil 25 and the second supplementary coil 26 is like that of the first coils 21, 22, in that the turns of the supplementary coil 26 are of lesser number and in opposition to the turns of the main coil 25. The coils are further arranged so that the

main coils

21, 25 have their .fields add toone another.

.set the reed switch will open.

, h In operating the reed switch of FIG. 4 both the first .and second set of coils must be operated to close the reed contacts, and upon deenergization of either set of

coils

21, 22 or 25, 26 the contacts will reopen. Thus, for

example, if the first set of

coil sections

21, 22 be energized .with terminal 23 negative, the magnetic flux established This retention of open contact position results from the presence of the magnetic plate 11, and .as in FIG. 1 the pattern. of the magnetic field in the vicinity of the reed contact ends is modified by the presence of the surrounding magnetic plate 11 to prohibit the value for the magnetic flux between

reeds

2 and 3 from developing a force between the reeds sufiicient to close the switch.

. Upon energizing the second coil set, the

reeds

2, 3 will close. The magnetic flux of the second main coil 25 established in the right hand reed 3 is cumulative to that of the first main coil 21, so that for the flux path extending from reed 2 to reed 3, the magnetic intensity between

reeds

2, 3 is sharply increased and an attractive force sufiicient to close the reed contact ends 6, 7 is attained.

Now, upon deenergizing either the first or second coil The reversed supplementary coil which remains energized, such as the coil 22 in the event the second set of coils 25, 26 are deenergized, will cause a greater reduction in the magnetic forces between the closed relay contacts to ensure an .operation.

An example of the use of several reed switches with one flux diverting magnetic plate is shown in FIG. 5. A

mounting block 30 which may also serve as a terminal block, supports a pair of non-magnetic shafts 31 and 32.

The shafts 31, 32 are each threaded at one end to support a magnetic plate 33, which functions as the plate 11 of FIGS. 1, 3 and 4. A group of three glass enveloped reed switches are inserted in appropriate openings in the magnetic plate 33, and parts of the middle assembly are broken away to show one of these switches 34.

Coil assemblies

35 and 36 are placed over the reed switch '34, one oneach side of theplate 33. The particular coil assembl'ies.,35.and 36 have .coil sets, similarly as in FIG. 4, and for thecoilassembly 35 .a main operating winding 37 of one. coil set .is shown wound about a smaller sup plementary winding 38 of the other coil set. These coils are on a bobbin 39 that has one end abutting the plate 33, and its opposite end encircled by a non-magnetic assembly plate 40 that is drawn inwardly against the bobbin 39 by a non-magnetic assembly bolt 41. The bolt 41 extends through the plate 33 to a threaded engagement with a second non-magnetic assembly plate 42 which secures the coil assembly 36 in place. The

assembly plates

40, 42 also retain a second set of bobbin assemblies 43, 44 that are associated with and encircle an upper reed switch (not shown).

In some installations it may be desirable to extend the ferro-magnetic path of the magnetic plate 11, or 33, around the outer sides of the coil assemblies, and such an arrangement is shown in the lower part of FIG. 5 for the lowermost reed switch (not shown) that is encircled by a pair of coil assemblies 45 and 46. A pair of

magnetic tie rods

47 and 48 which pass through the magnetic plate 43 extend alongside the coil assemblies 45, 46. These

rods

47, 48 tie together

magnetic end plates

49 and 50, which encircle the outer ends of the coil assemblies 45, 46, and they are also encircled by magnetic tubes 51-54 which are held in tight abutting relation with the

plates

49, 50 and the plate 33. Thus, the

plates

49, 50 and the tubes 51-54, together with the

rods

47, 48 form magnetic circuits that extend from the flux diverting plate 33 around the outside of the operating coils to provide flux return paths bridging the ends of the individual reeds. In this modification stray air flux is greatly reduced so that magnetic interference between adjacent switches is correspondingly minimized. Compact assemblies can then be made without endangering reliability of performanoe.

When flux is established in a reed by an associated operating coil encircling such reed, the flux that leaks off the reed from near or at the contact end of the reed must extend back, around the coil to the opposite end of the reed. The plate 11 forms a segment of a path for this flux, which flux would otherwise be solely air flux. The low reluctance of the plate 11 modifies the pattern of the return flux by diverting substantial flux to the plate 11, and this flux diverting property of the plate 11 functions to affect the leakage flux leaving the reed. The effect upon the leakage field, then, is to reduce the working flux between the reed contact ends when one coil is energized, to thereby preclude switch closure.

The plate 11 must be of sufficient thickness, and the opening 10 must have small enough diameter, to divert enough leakage flux to sufficiently reduce the net closing forces acting upon the reeds. For general design purposes the plate 11 should be dimensioned to have sufficient diverting properties for ampere-turn values greater than any anticipated overload, but this is no particular design problem since adequate diversion is readily obtained for ampere-turn values reaching the physical limit of the coils. As an example, for a readily available 0.2 inch diameter reed switch having a contact overlap of .05 inch, a plate inch thick will provide good performance for the coil arrangements of FIGS. 1 and 4. It can be generalized for these arrangements that the width of the magnetic flux diverting member should be at least as great as the overlap of the reed contact ends. For the embodiment of FIG. 3 utilizing latching magnets the flux diverting plate should be of increased thickness, and it has been found that a 4 inch thickness gives good results for a 0.2 inch diameter reed switch.

It is desirable to proportion each operating coil to develop a magnetizing force that substantially saturates the associated reed when drawing rated current, and economical use of both the coil and reed materials may then be achieved. The reeds may also be designed to magnetically saturate with a small increase of ampere-turns over that which is sufiicient for closure. Then, increased excitation of the coil will not produce large increments of flux at the reed contact ends, so the flux diverting plate is not called upon to handle excessive amounts of flux under overload conditions of the coil and the flux through the contact ends to cause contact closure will not increase markedly.

For the device of FIG. 4 the smaller supplementary coils may be placed inside the main coils, as shown for

coils

37 and 38 in FIG. 5, or they may be placed toward the center of the envelope 1, as schematically indicated in FIG. 4. Their modifications of the magnetic field may then affect switch operation while remaining at a number of turns substantially less than the number of main coil turns. For the concentric arrangement of FIG. 5 a ratio of from two to one to four to one for the main coil turns to the supplementary coil turns has been found satisfactory for usual operation, and the axially inner ends of the coils should be set back from the flux diverting plate for about inch for a reed switch of the above discussed dimensions.

In summary, the invention provides a reed switch control, in which two signals are required for initial switch operation, making novel use of a fiuX diverting member positioned at the reed contacts to modify the magnetic field, and this in turn provides for elimination of critical operating limitations. Further, supplementary coils can be employed to insure proper opening action for an and logic circuit element.

I claim:

1. In 'a control for a reed switch having a pair of magnetic reeds which have relatively movable, facing, normally open contact ends, the combination comprising: a pair of operating coil means one encircling each of the reeds and disposed on opposite sides of the contact ends, each of said coil means establishing magnetic flux in its associated reed that passes in part across to the other reed to develop an attractive force between the contact ends, which magnetic flux is cumulative with that established by the other coil means, said reeds comprising the dominant magnetic flux paths of magnetic material through the centers of said coil means; flux diverting means disposed closely adjacent to the contact ends between the coil means that provide a region of low reluctance in the path of magnetic flux branching from the reeds in the vicinity of the contact ends; and latching magnet means disposed near the contact ends to establish magnetic'fiux that develops an attractive force between the contact ends that is cumulative with the forces established by the coil means and that is insulficient to move the contact ends to closed position when neither coil means has been energized but is sufficient to hold the contact ends against moving from closed position to open position, said flux diverting means diverting flux from passing from one reed contact end to the other upon energization of one coil means to tend to prevent contact closure, the diversion being such that the ratio of ampereturns necessary for contact closure when only one coil means is energized to ampere-turns necessary for each coil means for closure when both coil means are energized at substantially similar levels is at least approximately 3 to 1.

2. In a control for a reed switch having a pair of magnetic reeds which have relatively movable, facing, normally open contact ends, the combination comprising: a pair of operating coil means, one encircling each of the reeds, disposed on opposite sides of the contact ends, each of said coil means establishing magnetic flux in its associated reed that passes in part across to the other reed to develop an attractive force between the contact ends, which magnetic flux is cumulative with that established by the other coil means, said reeds comprising the dominant magnetic flux paths of magnetic material through the centers of said coil means; flux diverting means disposed closely adjacent to the contact ends between the coil means that provide a region of low reluctance in the path of magnetic flux branching from the reeds in the vicinity of the contact ends; and permanent latching magnet means comprising at least two magnets disposed between the coil means and on opposite sides of said flux diverting means, with opposite poles facing the flux diverting means, said means establishing magnetic 'flux that develops an attractive force between the contact ends that is cumulative with the forces established by the coil means and that is insufficient to move the contact ends to closed position when neither coil means has been energized but is sufiicient to hold the contact ends against moving from closed position to open position, said flux diverting means diverting flux from passing from one reed contact end to the other upon energization of only one coil means to tend to prevent contact closure, the diversion being such that the ratio of ampere-turns necessary for closure upon energization of one coil means to the ampere-turns necessary for each coil means for closure when both coil means are energized at substantially similar levels is at least approximately 3 to l.

3. In a control for a reed switch having a pair of magnetic reeds which have relatively movable, facing, normally open contact ends, the combination comprising: a pair of operating coil means one encircling each of the reeds and disposed on opposite sides of the contact ends, each of said coil means establishing magnetic flux in its associated reeds that passes in part across to the other reed to develop an attractive force between the contact ends, which magnetic flux is cumulative with that established by the other coil means, said reeds comprising the dominant magnetic flux paths of magnetic material through the centers of said coil means; flux diverting means disposed closely adjacent tothe contact ends between the coil means that provide a region of low reluctance in the path of magnetic flux branching from the reeds in the vicinity of the contact ends; and latching magnetic means with a biasing flux disposed near the contact ends to establish magnetic flux that develops an attractive force between the contact ends that is cumulative with the forces established by the coil means and that is insufficient .to move the contact ends to closed position when neither coil means has been energized but 'is suflicientto hold the contact ends against moving from closed position to open position, said flux diverting means diverting flux from passing from one reed contact end to the other upon energization of one coil means to tend to prevent contact closure, said flux diversion and said biasing flux being such that the ratio of ampere-turns necessary for contact closure when only one coil means is energized to ampere-turns necessary for each coil means for closure when both coil means are energized at substantially similar levels is at least approximately 3 to 1.

References Cited by the Examiner UNITED STATES PATENTS 2,187,115 1/40 Ellwood et al 20087 3,008,020 11/61 Mason '200'87 3,061,696 10/62 .Peek '20093 3,070,677 12/62 Lowry 20087 3,075,059 1/ 63 Blaha et al 200-87 3,114,008 12/ 63 Petersen et al '20087 3,141,079 7/64 Lowry 20087 BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

Claims

1. IN A CONTROL FOR A REED SWITCH HAVING A PAIR OF MEGNETIC REED WHICH HAVE RELATIVELY MOVABLE, FACING, NORMALLY OPEN CONTACT ENDS, THE COMBINATION COMPRISING: A PAIR OF OPERATING COIL MEANS ONE ENCIRCLING EACH OF THE REEDS AND DISPOSED ON OPPOSITE SIDES OF THE CONTACT ENDS, EACH OF SAID COIL MEANS ESTABLISHING MAGNETIC FLUX IN ITS ASSOCIATED REED THAT PASSES IN PART ACROSS TO THE OTHER REED TO DEVELOP AN ATTRACTIVE FORCE BETWEEN THE CONTACT ENDS, WHICH MAGNETIC FLUX IN CUMULATIVE WITH THAT ESTABLISHED BY THE OTHER COIL MEANS, SAID REEDS COMPRISING THE DOMINANT MAGNETIC FLUX PATHS OF MAGNETIC MATERIAL THROUGH THE CENTERS OF SIAD COIL MEANS; FLUX DIVERTING MEANS DISPOSED CLOSELY ADJACENT TO THE CONTACT ENDS BETWEEN THE COIL MEANS THAT PROVIDE TO REGION OF LOW RELUCTANCE IN THE PATHER OF MAGNETIC FLUX BRANCHING FROM THE REEDS IN THE VICINTITY OF THE CONTACT ENDS; AND LATCHING MAGNET MEANS DISPOSED NEAR THE CONTACT ENDS TO ESTABLISH MAGNETIC FLUX THAT DEVELOPS AN ATTRACTIVE FORCE BETWEEN THE CONTACT END THAT IS CUMULATIVE WITH THE FORCES ESTABLISHED BY THE COIL MEANS AND THAT IS INSUFFICIENT TO MOVE THE CONTACT ENDS TO CLOSED POSITION WHEN NEITHER COIL MEANS HAS BEEN ENERGIZED BUT IS SUFFICIENT TO HOLD THE CONTACT ENDS AGAINST MOVING FROM CLOSED POSITION TO OPEN POSITION, SAID FLUX DIVERTING MEANS DIVERTING FLUX FROM PASSING FROM ONE REED CONTACT END TO THE OTHER UPON ENERGIZATION OF ONE COIL MEANS TO TEND TO PREVENT CONTACT CLOSURE, THE DIVERSION BEING SUCH THAT THE RATIO OF AMPERETURNS NECESSARY FOR CONTACT CLOSURE WHEN ONLY ONE COIL MEANS IS ENERGIZED TO AMPERE-TURNS NECESSARY FOR EACH COIL MEANS FOR CLOSURE WHEN BOTH COIL MEANS ARE ENERGIZED AT SUBSTANTIALLY SIMILAR LEVELS IS AT LEAST APPROXIMATELY 3 TO 1.