US2034701A - Relay - Google Patents

Description

P. L. S. LUM

March 24, 1936.

RELAY Filed March 27, 1934 2 Sheets-Sheet l MalCh 24, P. l s. LUM .Y v RELAY Filed March 27, 1954 2 Sheets-Sheel 2 ATTORNEY Patented Mar. 24, 1936 UNITED STATES PATENT OFFICE RELAY Philip L. S. Lum, Chatham, N. J., assignor to L. A. B. Corporation, Newark, N. J., a corporation of New Jersey This invention relates to improvements in relays and more particularly to devices of this character which are adapted to be used in connection with alternating currents.

Polarized relays for direct current are very well known and in most cases make use of a magnetized piece of steel or permanent magnet to obtain polarization.

I'here are also known certain types of polarized A. C. relays, most of which however areadapted to only one special purpose and are very limited in their usefulness.

An object of the invention is to provide an alternating current relay that has extremely high sensitivity and which will respond to current impulses which are too weak to operate any ordinary relay. Another object is to provide a relay which is adapted to discriminate between currents of different signs; in other words, which will react in one way if current flows in' one direction and which will react in a different Way if the current flows in opposite direction. Generally such relays are called polarized relays as polarization of certain parts of the relay is used to obtain the desired effect of sensitivity to currents of different signs. i

Other objects of this invention, not at this time more particularly enumerated, will be clearly understood from the following detailed description of the same.

The invention is clearly illustrated in the ac-V companying drawings, in which:

Fig. 1 is a front elevation with certain parts in section showing a preferred form of relay embodying this invention; and Fig. 2 is a side elevation of the same with some portions omitted and others in vertical section.

Fig. 3 is a similar front'elevation, and Fig. 4 a similar side elevation, with parts in section, but showing another form of relay according to this invention.

Fig. 5 shows a schematic circuit diagram of a i relay connected for use. Fig. 5 shows an arrangement of multiple contacts for relay and the corresponding schematic circuit diagram, the

core and windings being omitted. Fig. 7 is a/ fragmentary side elevation of a portion of the structure of Fig. 6. Fig. 8 shows the same relay connected for use as a differential polarized relay of insulating material such as bakelite, slate, marble, or the like, and 2 is a core of magnetic material built up to the desired thickness preferably out of insulated laminations in a similar way as transformer cores are constructed. The 5 laminations are held together by rivets 3 and the whole core is mounted upon the base plate I by means of the screws 4 and spacers 5. Upon this core are mounted two coils 'I and 8 shown in section. 'Ihese two coils are electrically'connected 10 in series and their sense of winding is such that the fields created by each coil are in the same direction and therefore ladd up. The free terminals of the coils I and 8 are connected respetively to terminal posts 9 and I0. 15

A clamp II is mounted on the core 2 by means of screw 6 and serves the purpose of holding a thin spring steel hinge I2 which is connected rigidly to the clamp II by means of screws I3. An armature I4 is rigidly connected to the free 20 end of the spring hinge I2 by means of rivets I5, and can swing freely in the free space within the hollow core of the bobbin I6.' This bobbin is made of insulating material and is mounted rigidly on the core 2 by means of screws -I 'I 25 and I8. A pin I9 is fixedly inserted into the free end of the armature M and this pin is slotted at its free end. Into this slot is .inserted a nonmagnetic spring leaf 20 that is riveted to the pin I9 or soldered to it. The free end of this spring 30 leaf 20 is provided with a double sided contact 2I which protrudes on both sides of the spring leaf. Adjacent to this contact 2|, but separated from it by an air gap, are two stationary contact screws 22 and 23, each of which is mounted in a 35 threaded hole of the posts 24 and 25 respectively. The posts 24 and 25 are mounted on the base plate I and are split at their outer end portions and through the axis of the threaded hole so that the contactscrews 22 and 23 will be gripped, due 40 to the spring action of the two halves of the slotted posts and held safe against vibrations.

'I'he bobbin I6 carries one or more windings, the impedance of which depends on the purpose for which the relay is intended. If the source of supply for these windings is of high tension but of very small current capacity, the number of turns would be high and the diameter of the wire used very small so as to insure high impedance of the coil and high number of turns. If the supn ply, however, is of low voltage but of relatively high current capacity, a few turns of heavy wire would be used, Depending upon the purpose of the relay, whether itis to be used as a simple polarized relay or as a differential polarized relay,

one or more coils can be used on bobbin I6. .I

, have shown two coils 32 and 33 as this' will provide the possibility of using the relay in different combinations. These coils are hereinafter referrcd to as operating' coils. The ends of the coils are brought to terminals 26, 21, 28, and 29 so as to be available for outside connections. Terminal 30 has been connected with the metal frame 2 of the relay. i

It will be understood that the armature I4 can move to the right and to the left until the contact 2| touches either contact 22 or contact 23 and that if further forces are acting onthe armature, the spring leaf 20 by flexing will allow the armature to keep on moving until it is blocked by the insu# If now an alternating current is sent through the coils I and 8 which are hereafter called the polarizing coils, an alternating flux will be set up in the core 2 and in the air gap between the pole ends 3| and 3 I The highest eld concentration will be directly between the tips of the pole ends and will bulge out from their normal to the axis of coils 'I and 8. It is obvious, therefore, that the free end of the armature I4 will be located in the bulging or extending part of the magnetic eld and that this field will exert a longitudinal pull upon the armature, trying to pull it into the air gap between the poles 3| and 3|', but without moving it sideways. That part of the pole ends 3| and 3l which faces the armature is recessed cylindrically as shown and in such a way that the armature I4 can never come into direct contact with the core.

If now an A. C. ,of equal frequency and phase as the polarizing A. C. is introduced into the operating coils 32 and 33 so as to magnetize the armature I4, the armature will move sideways in a definite direction depending upon the direction of flow of current in coils 32 and 33. If we assume that both these coils are connected in series and so as to add up `their eect upon the armature I4, and if we further assume that tip 3| at a given moment is a north pole while tip 1 3| at the same time is a south pole, and that the free end of the armature I4 at the same given moment assumes north polarity, then the armature will move toward the tip 3| under the influence of the two different magnetic fields cre- Y ated by the two different currents.'

It is easily understood that the magnetic ux created in the armature by the current through the coils 32 and 33 has to pass through the core 2 in order to complete its path. Therefore, this ux will add to the field of coil I and subtract from the eld of coil 8, thereby unbalancing the center of pull of the main magnetic field between the tips 3l and 3`I' and shifting this center towards tip 3|. Inasmuch as during the next half cycle all polarities in all coils change at the same time, the armature will, during the next half cycle, be moved in the same direction as in the rst half cycle. Its inertia will be suilicient to prevent it from snapping back into the zero position, provided the frequency of the currents is high enough to make one-half cycle short as compared to the mechanical time constant of the armature and spring.

Inasmuch, as during its motion the armature does not approach the tip 3| but stays substan` tially at the same distance therefrom, there would be no increase of the magnetic ux and no resulting acceleration to the armature. This means that the armature will not snap over, but will move gradually and assume a definite point of rest, in which the force of the unbalanced or shiftedmagnetic field is equal to the restoring forces of the spring hinge I2. The eiect of the spring hinge I2 can be compensated for to any desired extent by shaping the pole ends 30 and 3| so that there is a slight decrease in the distance of the armature from the poles the more the armature moves out. If this decrease is made too much the resulting increase in magnetic flux density will overcome the restoring forces of the spring entirely and the armature would ybe accelerated from its normal position, resulting in a snap action of the armature. The snap action of the armature results in quick motion but the operating current through coils 32 and 33 would have to be decreased considerably before the armature would snap back into its normal position.

If, on the other hand, the shape of the pole ends 3D and 3| is such as to compensate for only part of the spring action, the position of the armature will depend entirely upon the amount of current through the coils 32 and 33, or the angular motion of the armature under the iniiuence of the operating current would beA a function of the sign as well as the amplitude of the current, because it is easily understood that a reversal of the current through coils 32 and 33 u will move the armature toward pole end 3|. the poles are shaped so that the free space between the free end of the armature and the poles tends to increase, the motion of the armature under the influence of a rising operating current will be such that the armature will not move beyond a certain point, i. e. the point at which the increase of spring tension is greater than the increase in total magnetic force. v

These characteristic actions of the relay can be used to advantage if it is desired to obtain from the relay indications not only of the sign of the iiow of current through the operating coil but also of the amount of current at any given moment. Fig. 6 shows how this can be done.

The armature I4 is designed the same way as rin Figs. 1 and 2 but the pin I9 carries five contact springs instead of only one, the leaf 2U. Spring leaves 34, 35, 36, and 31 have been added. 'Ihese spring leaves are all free at one end and spaced apart from each other and are all connected together to the pin I9 at the other end.

Spring 20 as before carries a double sided contact 2| but the other springs carry single contacts as shown. Opposed to each of the contacts are contact screws, so that the contact car-` ried by leaf 34 can make connection with contact screw 38; 35 with 39; 36 with 40; and 31 with 4I. Contact screws 22 and 23 are in the same place as before but they are now mounted in insulating pieces or brackets 42 and 43, respectively, together with the other contact screws. Split metal bushings 44 have been inserted into the insulating brackets 43 and 42 and from each of these bushings extends a wire to provide for outside connections. The brackets 42 and 43 are mounted on the base plate I by means of screws 45.

The action of this multi-contact armature under the influence of a rising operating current through coils 32 and 33 is now as follows: If we assume that the direction of the operating current is such as to cause armature I4 to move to the left in Fig. 6, contact 2| will be the first to make contact with its adjacent screw 22,

aos-w01 while the contact on leaf will connect with contact screw 39 after the armature has moved a little further. At that time both the contacts 2| and 35 are engaged. If the current still continues to rise, the contact 34 would encounter contact 38 and all three contacts at that time will be engaged together. If the operating current now gradually decreases, contacts 38-34 will open rst, then contacts 39-35 and then contacts 22-2I. As soon as the operating current reaches zero, the armature will be in its normal position and if the operating current now reverses its sign and increases again, the same procedure to the right of Fig. 6 will take place in similar sequence.

Irrespective of the number of contacts upon the armature, it should be understood that, having an armature which moves to a certain extent proportional to the sign at the amplitude of an operating current, the response of the armature will be immediate upon the change of the amount of current. As explained before, the pole ends could be shaped so that `the armature would move with a snap or with acceleration resulting in quick make and break, but appreciable changes of current would be necessary to move the armature out of its once assumed position. It either would go the full way or not at all, and after it has gone the full way the current would have to be reduced considerably in order to allow the spring to move the 'armature back. However, with the armature moving nearly prov portional to the current a snap action is impossible and the armature will respond immediately, and this response will be a function of the amount and direction of the current.

Figs. 3 and 4 show another preferred form oi the relay. In al1 essentials except the armature it is constructed as that shown in Figs. l and 2. The armature 46 is not hinged to the core 2 as before but pivoted as shown. The

laminations of the core 2 extend .all the way through the operating coils 41 and 48 in the shape of an extension 49. Two flat metal strips or plates 50 and 5| are shaped so as to extend slightly beyond the core V49 and carry atA their extreme end two y"screws 52 and 53 respectively. 'I'hese screws are held against rotation by means of check nuts 54 and 56 and extend beyond the plates 5| and 50. Their inner ends are hard-` ened and countersunk and between these two points swings the armature 46 which is fastened to the needle point pivot 55. If correctly adjusted such bearings have substantially the least possible friction of all known bearings and pro- .vide a very satisfactory means of attaching the varmature 46 to the core 49. Due to the comparatively large cross-section of the core 49 a 'rather high magnetic fiuxcan be generated in the armature by a comparatively weak alternating current through the coils 41 and 48. A- pin 51 is inserted into the free end of armature 46 andcarries a spring leaf contact 58 which is similar as described for Fig. 1 and Fig. 2. There is no mechanical centralizing force on the'armature 46, as there is no spring hinge and no other restoring spring. The centralizing force for this armature is provided for bythe magnetic field between vthe pole ends 3| and 3|', which are shaped so that in its normal or zero position the end of the armature is nearest to the pole ends but sufficiently far away from both to beI only under the influence of that part of the field which bulges out and curves away from the pole tips. If this were not the case the `armature coils, while the midpoint would try to assume a position either nearest to one or the other pole tip and would not have a normal zero position. The poles are shaped so that the distance of the free end of the armature from the poles increases with increasing angle of motion. In case of operating currents of varying amplitude the armature will follow the shift of maximum pull of the polarizing field and its angular motion will be proportional to the sign and the amplitude of the operating current. This type of relay also can be provided with multiple contacts as shown in Fig. 6.

It is also possible to construct a relay of the above described characteristics by using separate cores for the different magnetic circuits and by connecting these cores in such a way, that the ux will be conducted to the desired points. Such a relay is shown in Figs. 9 and 10. The polarizing coils'96 and 97 are mounted on pole pieces 98 and 99, which in turn are riveted to the U-shaped steel yoke or core frame |00. The operating coil |0i is mounted on the same core frame |00 which frame in effect becomes an extension of core 98-99. The armature |02 is suspended substantially midway of its length between pivot screws H3 and H4 and can swing within the hollow operating coil |0l. If this armature l0? and the spring leaf contact H5 carried thereby are suspended so that the same is completely balanced, the assembly will be substantially vibration-proof,

The contacts are arranged at that end of the armature, which is not influenced by the polarizing coils, but their action is identical with those of the aforedescribed relays. Terminals |03, |04, |05, |06, |01, and |08 are provided and fastened to the base |09, which is made of insulated material. Terminals |03 and |06 serve the polarizing coils, and terminals |04 and |07 serve the single operating coil, but their wire connections are concealed in the base and not shown. Terminals |05 and |08 are fastened to the contact carriers ||0 and and serve for the secondary circuit. The frame |00 serves as the electr'cal connection for the center Contact on the arma'- ture and a wire may be fastened under the nut ||2 holding this .frame to base |09. This type of relay also may be provided with multiple contacts as shown in Figs. 6 and 7. Although, only one operating coil is shown in Figs. 9 and 10, as anyone skilled in the art will readily see, two lsuch coils could be wound on the same bobbin, if desired.

Fig. 5 shows one of the many possible uses for the polarized relay.- In a diagrammatic way the solid iron core of the relay is shown as a solid line 59 and the armature is shown at E0.. 6| and 62 are the polarizing coils and 63 and 64 are the operating coils. As shown in the diagram, an A. C. supply is represented by the two lines 65 and 66. The polarizing coils 6| and 62 are energized from the supply through a. variable resistance 61, the purpose of which is to vary the iield strength in the air-gap in order to obtain perfect balance of the magnet'c circuits. The operating coils 63 and 64 are shown as connected in series so that their respective elds are adding up. The slider of a potentiometer 69 is connected to one free terminal of the operating 'l0 of the same potentiometer is connected to the other free' terminal of the operating coils. 'Ihe potentiometer itself is energized from the supply lines 65 and 66. In the position shown, where the slider 68 is directly on the midpoint l0 of the potentiometer,

no current is flowing through the operating coils. Therefore, the amature will remain in its neutral position.

If now the slider 68 is moved slightly toward one side of 'the potentiometer, a current will flow in a certain direction through the operating coils and thereby cause the armature to leave its central position. If we assume that the polarities of the polarizing and the operating coils are such that the armature will move toward the left, contact 1I will connect with contact 12. 'This will close a secondary circuit which goes from the negative terminal of battery 19 through the amature 89 and the contact spring, through contacts 1I and 12 and from there to the lamp 15 from where the circuit is closed by the return wire to positive terminal of battery 19. Lamp 15 will glow as long as contacts 1l and 12 are touching. If the slider 68 is moved further out in the same direction as before, the` current through coils 63 and 89 will increase and the armature will try to move further to the left. This will ex the contact spring and contact 1I will slide slightly over contact 12. By reversing the motion of the slider it will gradually approach again point 10 and at this point the armaturewill have broken the contact and be back at its neutral position. Continuation of the motion of the slider in this direction, which means toward the other side of center point 18, Will reverse the direction of ow o current through the operating coils and thereby move the amature now to vthe right. At a certain position of the slider 68 the armature will have moved far enough to make contact 1I touch contact 13 whereby the lamp 16 is lighted. i

It is, therefore, possible by means of this relay, to indicate at a remote point the motion of the slider 68 with respect to the center point 10 on the potentiometer 89. The slider may be connected to an important operating part of some industrial installation, for instance a valve or a float on the surface of some liquid or anything which normally has a neutral position. Any departure from this neutral position would be indicated at any` given remote point by the lights I5 and 16 which naturally could also be duplicated by parallel lights so as to have indications at diierent points.

The possibilities of uses for the proportional motion of the armature with respect to the amount of current flowing through the operating coils can be best demonstrated by Fig. 6 which contains also a schematic wiring diagram for the use of this relay to control a number of remote indicating lamps. These lamps are used in a similar manner as shown in Fig. 5, but instead of having one lamp for each direction of current in the operating coils, three lamps for each direction are used here in such a manner, that the number of lights burning simultaneously denote the quant'ty of current flowing. The electrical connections for the coils of the relay proper are identical with those shown in Fig. 5. But instead ofA using but one lamp 18 in Fig. 7, there are three lamps 89, 8l, and 82 in Fig. 6, and for lamp 15 in Fig. 5 there are substituted three lamps 11, 18, and 19 in Fig. 6,. Lamps 88, 8l, and 92 are shown connected to contact screws 23, 48, and 4 I while the lamps 11, 18, and 19 are respectively connected to contact screws 22, 39 and 38.

The electrical connections of the relay itself, the major part not being shown in Fig. 6, are, as mentioned, identical with those of Fig. 5. It will be clearlv understood that if the armature is un- Yterminal of the battery aolsavoi der the inuence of a slowly rising control voltage caused by motion of a slider similar to slider 88 in Fig. 5, which voltage tends to move the armature in Fig. 6 toward the left, that contact 2l will be.

the i'lrst to make connection with contact 22 and at that time start a current to flow from the negative terminal of battery 83 through the armature and the contact spring 28, through contacts 2i and 22, through lamp 11 and from there through the common connection 89 back to the positive 83. If the current through the operating coils of the relay further increases, the armature will move further to the left and cause contact spring 35 to make contact with the screw 39, thereby energizing lamp 18 also. Both lamps 11 and 18 are now glowing. Further increase of the operating current will move the armature I9 still further to the left until contact spring 38 connects with contact screw 38 and thereby lights also lamp 19. Gradual decrease of the current through the operating coils of the relay will move armature I 4 back toward its neutral position and first open the contact between 38 and 38, then the contact between 35 and 39, eachtime extinguishing one lamp. Finally the contact between 2 land 22 will be brokenv and all lamps will be out.

If now the current through the operating coils isreversed by moving the slider similar to slider 68 in Fig. 5 beyond the center point towards the other end of the potentiometer 89 and starts to increase from zero in the opposite direction, the armature I4 will move toward the right and consecutively close the three contacts associated with the screws 23, 40 and 4I. 'I'his in turn will consecutively energize lamps 80, 8|, and 82, so that finally all three lamps are lighted. It is therefore possible, by means of the polarized relay, to indicate at a remote point the position of the slider 68, at least in so far as the six lamps will show definitely, that the slider has reached lor passed a vcertain point. Anybody skilled in the art can imagine the numerous possibilities of connecting the control slider 68 with some important manipulation which has to be watched or known.

As shown in Fig. 8, which again shows a schematic wiring diagram of the relay, it also can be used as a dilerential polarized relay. In this case the operating coils 63 and 64 are connected in such a way that their fields oppose each other. If the total number of ampere turns and the impedance of the coils are identical, no' magnetization of the arma-ture will result as long as the currents owing through each coil are equal in amplitude and opposite in direction of ow. As shown in Fig. 8, the common connection between coils 63 and 84 is connected to line 65 of the A. C.

supply. 'Ihe free end of coil 64 is connected to the control slider 89 on potentiometer 98, while the free terminal of coil 83 is connected to the slider 92 on potentiometer 93. Both potentiometers are energized from the common A. C. supply 66 and 69. As long as the sliders 89 and 92 are positioned so that the potential between slider 89 and point 94 is equal to that between slider 92 and point 99, the currents through coil 63`and `coil 84 will be equal and opposite and their eiect on the armature will be zero. If slider 89 is now moved toward the terminal 95 of potentiometer. 90, the current through coil 64 will decrease while the current through coil 63 stays constant. In

y coil.

the more the armature would be moved out of its central position toward one side. Reversal of the motion of slider 89 will bring the amature back progressively toward the neutral point, and as soon as the potential between 89 and 94 becomes again equal to that between 92 and 94, the armature will have reached its zero position. If the slider 99 is now moved toward the terminal 96 of potentiometer 90, the armature would be moved off its neutral point toward the other side. Motion of the slider 92 would have a similar eect. The secondary circuit, controlled by the contacts ll, 12, and '13, could be similar to that in Fig. 5, and therefore is omitted in Fig. 8. 'I'his relay also could be equipped with multiple contacts, as shown in Fig. 6.

From the foregoing description of the secondary circuits of the relay it is obvious how the differential relay also could be used to control lights or other apparatus or any other suitable instruments which it is desired to control by means of the motion of the sliders 89 and 92. It is obvious, however, that the differential polarized relay allows the comparison between two A. C. currents or different sources but of equal frequency and phase and to find whether the current to be compared is higher or lower than the standard of comparison and to actuate from the relay means to indicate. directly or indirectly such differences.

It is also evident, that the relay of Fig. 5 will vrespond to a change of phase between the current in the operating and the current in the polarizing coils. If the phase angle is the armature of the relay will be in its neutral position, or very near that position. If the phase angle is either zero or the armature will be at one or the other extreme end of its possible sweep. Angles of phase in between the just mentioned angles will result in intermediate positions of the armature, which therefore could be used as a phase angle indicator, so that it could signal any departure of the 90 phase angle of one current against another current, if such a problem should come up.

'I'he relay in Fig. 8 could serve a similar purpose, by signalling the change of the phase angle of the current in one operating coil against'the phase angle of the current in the other operating As the armature in Fig. 8 will be at its neutral position only, if the two currents are of opposite phase, any change of the phase angle of one o f the currents would immediately actuate the relay. 'I'his can be utilized where it is important to watch the power factor of an important circuit.

It is also evident that the functions of the operating coils and the polarizing coils can be exchanged without materially changing the characteristic action of my relay.

II oneconsiders direct current as a special case of alternating current, namely as an alternating current with zero frequency, it becomes evident, that the above described relay, will be universally adapted for all types of current, without any change of their operating characteristics.

As manyv changes could be mad'e in the above construction and many apparently widely different embodiments of this invention could be made withoutk departing from the scope thereof, as defined by the following claims, it is intended that all matter contained in the above description or shown in the accompanying' drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a relay, a core having an airgap, means to maintain a magnetic field of selected fixed average value in and around said airgap, an armature mounted on said core and adapted to move entirely exteriorly of but adjacent to said core airgap and to be normally held in a central position, means to produce in said armature a magnetic eld variable as to sign and intensity so as to cause motion of 4said armature from its central position, said motion being proportional to the sign relationship of said last named field to that of the core eld and to a function of the intensity of said armature field.

2. In a relay, comprising a core having pole extensions providing an airgap therebetween, polarizing windings on said core, a source of potential energizing said windings to maintain a magnetic eld of selected fixed average value in and adjacent vto said core airgap, a movable armature mounted on said core having its free end adapted to move entirely exteriorly of but adjacent to said airgap and to be influenced by said field so as to assume a normally central position close to the point of highest field intensity, operating windings to independently magnetize said armature from. a source of supply having substantially the same phaseand frequency as said first named source, means to vary the magnetizing current through said operating windings to produce in said armature mechanical reactions proportional to the sign of said current and to a function of its amplitude.

3. A relay comprising a core and a movable armature mounted on said core, said core having an airgap adjacent and normal to one movable end of said armature, said armature being positioned exteriorly of said airgap and never entering the same polarizing windings on said core energized from a current supply to produce a magnetic 'iield in and adjacent to said airgap, operating windings independently energized from said supply to magnetize said armature7 means to vary the current through said operating coils as to sign and value to produce mechanical motion of said armature substantially proportional to the sign and the value of said current, and a plurality of contact means associated with said armature, certain of said contact means being carried by said armature and adapted to cooperate with others of said contact means arrangedso as to be engaged successively depending upon the extent of motion of said armature, and adapted to operate secondary circuit means.

4. A relay, comprising a core having an airgap between two pole extensions thereof, an armature movably mounted on said core and adapted to move entirely exteriorly of and adjacent to said airgap, polarizing windings on said core, operating windings surrounding but not obstructing said armature, means independently associated with each of said windings to impress thereon polarizing and operating potentials of substantially equal phaseand frequency to produce in the armature reactions substantially proportional to the sign and the amplitude of said operating potential, a plurality of fixed contacts, and a plurality of contacts associated with said armature and adapted to successively engage with said plurality of fixed contacts arranged on either side of said armature, said contacts being ,adapted to operate secondary circuit means.

5. In a relay of the character described, core means having an airgap therein, a winding on said core means adapted to be energized so as to establish an alternating magnetic field within said airgap, an armature associated with said core means having a portion disposed to move adjacent to but outside of said airgap, said armature never entring said airgap, said armature being normally held in a neutral position by the magnetic field in said airgap, and winding means surrounding said armature and adapted for producing alternating flux therein to thereby cause said armature to depart from its neutral position.

6. In a relay of the character described, a core having an airgap therein, winding means on said core adapted to receive alternating current for establishing an alternating magnetic field of selected fixed average value in said airgap, an armature arranged to move adjacent to but outside of said airgap so as never to enter the same, said armature 'being normally held in a plane extending substantially at right angles to said airgap and midway of the width thereof, and windingA means surrounding said armature and adapted to be supplied with alternating current, said armature being electromagnetically associated with said core whereby i'lux set up in said armature by said last named winding means will pass through a portion t of said core, thereby causing said armature to move from its normal position, the extent of movement of the armature from its normal position depending upon the characteristics of the current passing through said last named windingmeans.

7. In a relay of the character described, a core having an airgap therein, winding means on saidcore adapted to receive alternating current for establishing an alternating magnetic field of selected iixed average value in said airgap, an armature arranged to move adjacent to but outside of said airgap so as never to enter the same, said armature being normally held in a plane extending substantially at right angles to said airgap and midway of the Width thereof, winding means surrounding said armature and adapted to be supplied with alternating current, said armature being electromagnetically associated with said core whereby flux set up insaid armature by said last named winding means will pass through a portion of said core, thereby causing said armature to move from its normal position, the extent of movement of the armature from its normal position depending upon the characteristics of the current passing through said last named winding means, contact means carried by and movable with said armature, and stationary contacts positioned for selective engagement by said movable contact means.

8. In a relay of the character described, core means provided with an airgap therein, a winding on saidcore means adapted to be supplied with yalternating current for establishing an alternating magnetic eld of substantially constant average value in said airgap, an armature movably associated with said core means and arranged to have one end movable adjacent but outside of said airgap so as never to enter the same, said armature being normally held by said field in a plane extending at right angles to said eld and substantially midway of the width of said airgap, winding means surrounding said armature and adapted to be supplied with alternating current,

said armature being electromagnetically associated with said core means, whereby flux set up in said armature by alternating current passing through said winding means will extend within said core means, said flux cooperating with the iiux set up by said core means winding, when an appreciable component of the current passing through said winding means is in phase with the current passing through said core -means winding, to cause movement of said armature from its normal position, the extent of movement of said armature being a measure of such current component. t

9. In a relay of the character described, core means provided with an airgap therein, a winding on said core means adapted to be supplied with alternating current for establishing an alternating magnetic i-leld of substantially constant average value in said airgap, an armature pivoted substantially at its center of gravity upon said core means and arranged to have one end thereof movable adjacent but outside of said airgap, said armature never entering said airgap, contact means carried by the other end of said armature, stationary contact means for cooperating with said armature contact means, said armature being normally held by said eld in a plane extending at right angles to 'said field and substantially midway of the width of said airgap, winding means surrounding said armature and adapted to be supplied with alternating current, said armature being electromagnetically associated with said core means, whereby ux set up in said armature 10. In a relay of the character described, core means having an airgap therein, winding means on said core means adapted to be energized by alternating current for establishing an alternating magnetic eld of substantially constant average value in said airgap, an armature movably associated with an extension of said core means and arranged to have one end movable adjacent but outside of said airgap so as not to enter the same, and normally held by said field in a plane extending at right angles to said field substantially midway of the width of said airgap, winding means surrounding said armature and adapted to be supplied with alternating current, the phase of which is normally in quadrature with the phase of said first named alternating current, so that departure of the phase relations of said currents from quadrature will cause said armature to move from its normal position and to assume a new position depending upon the amount of change of phase angle between said

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