US1680667A - Electromagnetic device - Google Patents

Description

Aug. 14, 1928. y f A. M. CURTIS ELECTROMAGNETIC DEVI GE 2 Sheets-Sheet Filed oo t. s. 1922 3 llllllllllllllllllllllllllllllllllllhm 4:v Opera/7h; Car/enf PatentedA Aug. 14, 1928.

UNITED STATES PATENT OFFICE.

AUSTEN M. CURTIS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC COMIANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF YORK.

ELECTROMAGNETIC DEVICE.

Application filed October 3, 1922. Serial No. 592,028.

This invention relates to an electromagnetic device and in particular to a sensitive relay especially suitable for use in connection with high speed telegraph lines.

It is the principal object of the invention to provide a relayof high sensitivity and one in which the residual magnetism of the magnetic circuit is reduced to the lowest point possible.

A preferred embodiment of the invention is described and illustrated in the following specification and accompanying drawing in which Fig. 1 is a plan view. Fig. 2 is a side elevation of the relay shown in Fig. 1. Figs. 3 and 4 are typical wave forms illustrated to aid in explaining the operation of the relay under various service conditions, and Fig. 5 shows graphically the contact pressures obtained with such a relay for given operating currents and also the residual effect due to various operating currents when employing different materials for the magnetic circuit. Recent developments in the design of long submarine cables have increased the need for a telegraph relay which is accurate and reliable when operated at high speeds with weak operating currents. According to this invention a very great improvement is 0btained bythe use of a new material for the `magnetic: circuit. An investigation has shown that there have been obtained by the use of this material unexpected improvements in the operation of relaysnot only of the type particularlyadapted for use with submarine cables but of types suited for more general use. In sending telegraph messages at high speed over long loaded telephone lines, as is customary in composited systems, the presence of the loading coils makes it necessary to keep down the amplitude of the telegraph current impulses in order to prevent making the lines noisy by producing what is commonly called Morse thump. Accordingly on such lines a relay is required of much higher sensitivity than is required on unloaded lines where it is not necessary to limit the amplitude of the current impulses. Again, in the operation of long submarine cables, the sending voltage is made as high as safety permits volts being the safe limit for ordinary operation for long cables) and with the sending voltage thus fixed, the l speed of sending is limited to that which will permit the receiving of legible signals.

In telegraph systems employed on long Submarine cables, particularly those designed to operate in connection with a printing telegraph receiver, it is very important to provide an accurate receiving relay which is con stant in adjustment. In suchv systems the wave forms of the received signal currents differ quite materially from the wave forms of the ordinary land telegraph lines. In such a cable the high frequencies are attenuated to a much greater extent than the lower frequencies and as a result the wave forms of the current pulsations instead of being square topped are rounded to more nearly approach a sine wave form. With a square top wave form the steepness of the wave front makes the point of operation of the relay quite certain, whereas with a rounded wave form the current wave does not forl some time reach the necessary amplitude to operate .the relay and the time of operation therefore will depend more or less upon the slope of the wave. Since the timev of opera- V tion of the relay is delayed somewhat it is desirable to provide a relay which will operate on currents of very small amplitude. When operating with signal impulses having a rounded vlave form, the time of operation is morel uncertain, as explained below, and, moreover, the time of contact closure also is less as a result of the comparatively slower movement of the armature. 4A square-topped wave having a steep front insures rapid acceleration of the armature and therefore a short period of armature travel, whereas with a rounded wave form the acceleration of the armature is less rapid and the period of contact closure correspondingly decreased.

lThe rounded wave form also produces the same uncertainty in the time of the release of the relay and makes it desirable to provide a magnetic circuit in which the residual effect is as nearly negligible as possible. The uncertainty in the time of operation and time of release of a relay operating on a currentl of rounded wave form, as well as the shorter period of Contact closure, results in distorted signals, which are especially serious when Yusing printing telegraph apparatus. If the signal is received on a tape, as for exam le, by means of a Siphon recorder, it is possi le for the receiving operator to diligently study the tape andl decipher the intended signal characters even though considerably distorted, but if a printing mechanism is employed aI substantially undistorted signal is required'in order that an intelligible message may be printed. Therefore in ordervto permit operation at high speed on such acable, the requirements call for a relay which is sensitive and uniform both in operation and in release.

The unsatisfactory operation of a relay on currents having rounded wave forms may be overcome to a large degree by increasing the current strength in case circuit conditions permit such a procedure. However, if this is done and the material of the magnetic circuit is worked at a correspondingly higher flux density, the residual magnetism becomes greater and further increases the `uncertainty of the point of operation of the relay.

In order to obtain eiiicient operation in cable circuits the use of the Gulstad vibrating circuit is often resorted to. When using the relay of this invention in this circuit, which is described in detail in the Electrical Review of London, volume 42, page 751, June 3, 1898, and volume 51, page 247, August 22, 1902, only sufficient current need be supplied over the line to control the action 'of a pair of windings since the circuit contemplates the use of local batteries to furnish'the operating current for the relay. By' the use of this circuit theoperation of the relay is materially im roved, especially in cable service. Not on y does the relay operate on2smaller line currents, but also there is much less distortion of the signals. However, with this circuit it is necessary to maintain the magnetic circuit of the rela highly balanced, since after the balance 1s upset the armature becomes biased, thus destroying the trigger action of the circuit andimpa'iring the operation of the relay. Such magnetic biases are likely to occur when the relay receives an abnormalvalue of current and the portion of the resulting iux which remains upsets the balanced action of the polarizing flux in the armatureof the relay. In accordance with this ini vention there is brought about a decrease in.

the residual magnetization of the relay employed in the Gulstad circuit resulting in an increased elciency in thel operation of the relay.

In the relay which illustrated in Figs.

1 and 2, thege is provided a mounting yplate 6 of non-magnetic material having lugs l to which are secured the L-shape pieces 8 and 9. VThe armature 10 is rigidly clamped between the rearends of the pole pieces by means bfscrews 11, 11, thin non.- magnetic shims 12, 12 being inserted as stop-pins 5-5 of brass or other non-magnetic material are v secured to the armature as shown. Attached to the free end of armature 10 are the contact springs 16, 16, the other ends of which are adapted, upon movement of the armature, to engage contact screws 17 17 supported upon suitable brackets 18, 18 which are insulated from the mounted plates by means of suitable insulating members 20, 20. The free ends of springs'16, 16 are adapted to be in sliding engagement with each other in order to overcome any tendency to chatter when the springs make contact with the contact screws. permanent magnet 21 is mounted on the lower side of mounting plate 6 and is joined in magnetic circuit with the pole pieces 8 and 9 by the magnetic members 22 and 23. The gaps at the rear of the magnetic circuit are equal and fixed, while the working air gaps at the front of the magnetic circuit nmay be very accurately adjusted by turning the adjusting screws 14, 15 which are provided with ine threads. In the operation f the relay, the armature is deflected or bent under the influence of the forces set up in the front magnetic air gaps by the polarizing and operating fluxes thus making and breaking contact with the contact screws 17, 17. The strength of the permanent magnet 21 is such that the pull exerted thereby upon the armature 10 is practically suiicient to counteract the stiness of the armature which is therefore substantially in equilibrium. f

The permanent magnet is preferably made from tungsten steel and the path of the polarizing iux through the magnetic circuit is from one limb of the permanent magnet through the `contact 'block 22 to the front end of pole piece 8. Here the iux divides into two paths, one is back through thc pole piece, across the two non-magnetic shims 12, 12 and the clamped end of armature 9 into polepiece 9 and thence to the other limb of the permanent magnet, through block 23. The other path is into the adjusting screw '14 across the working air gaps and the free end of armature 10 to adjusting screw 15 thence into pole piece 9 and returning to the other limb of permanent magnet through contacting block 23. It will be seen that both lthe amount and the direction of the polarizing A U-shapedv flux through the armature depends upon the position of the free end of the armature and the working air gaps. When the armature is exactly midway between the adjusting screwsfthere yis no polarizing fiux through the armature in the direction of its length since it connects two points of equal magnetic potential, but as it moves toward one adjusting screw, the polarizing flux flows through the armature in a positive-direction, whereas when it moves toward the opposite adjusting screw, the polarizing flux reverses and flows through the armature in a negative direction.

The paths of the operating flux, or that flux which is generated by currents traversing the operating windings, is out from the front end of armature 10 across the two working air gaps in parallel into the adjusting screws 14, 15, through the non-magnetic shims 12, 12 to the rear end of the armature. There is a third path for this operating flux through the permanent magnet, but due to the high reluctance of the permanent magnet as compared to that ofl the pole pieces, practically none of the fiux returns by this path. -It will be seen from the above that this relay differs from most all other types of polarized relays in that when the relay operates to deflect the armature from oneside to the other, both the operating flux and the polarizing flux reverse through the armature which accounts for the fact that the relay is highly sensitive to the magnetic characteristics of the armature. When employing silicon steel as the material for the armature 10 and a high grade of magnetic iron for the pole pieces 8 and 9 and the contact blocks 22 and 23 the relay operates on a very small current, but when -operating at high speed, the residual effect of the magnetic circuit slows down the operation and causes distortion. Thisresidual effect was first somewhat decreased by restricting the cross section of la portion of the .,armature, as shown at 25, but the operation bf the relay both as regards sensitivity and speed were"- still limited by the remaining residual effect. Tn 'fact it has beendetermined by careful tests that this remaining residual magnetism increases the minimum operating current approximately 8.7 times.

In Figs. 3 and 4 are shown typical wave forms representing respectively a squaretopped signal impulse usual in land telegraphy and a rounded top signal impulse as vpresent in long submarine cable systems.

The time scale for these curves is about fifty cycles per second, thus giving a single impulse in about onehundredth of a second. The position of the armature in relation to the contact members is shown by the lowerv curve in each of Figs. 3 and 4. At 25 the armature breaks contact at one side and swings across, and at 26 makes contact with the other side. Tt is inevitable that, due to temperature and other conditions, there will be-more or less uncertainty in the value of current at which the armature of the relay starts to move. Should it be assumed, for example, that in Figs. 3 and 4 operation will occuil at current values between points 27 and 28, this latter being twice the value of the former, this means that the operation will Ibedetermined within a range of time of less than half a thousandth of' a second for Fig. 3 with its square-topped wave, whereas the time range of uncertaintyl is nearly two thousandths of a second for Fig. 4. This comparison shows how the uncertainty as to ttie exact current values for operation gives much greater uncertainty for the time ot operation for the rounded top wave of Fig. 4 than for the square-topped wave of Fig. 3.

Another respect in which Fig. 4 shows at a disadvantage compared to Fig. 3 is that the time of travel of the relay armature will be longer for Fig. 4 than for Fig. 3. In Fig.

3 let it be assumed that the armature resting on one contactmoves away from that contact at 27. Some time will elapse for the armature to travel across from the position indicated at 25 to that indicated at 26, but within less than half a thousandth of a second the current will have risen to `double the value at which the break occurred, that is, from 27 to 28. This rapid increase of current produces a strong acceleration of the armature and causes it to movel quick-ly, as shown at 25 and 26. However, in Fig. 4 the elapsed time for the current to'double in value is nearly two thousandths of a second so that the travel of the armature will consume a longer time, as indicated from 25 to 26. Tt will be seen that the contact closure on one side for F ig. 3 from 26 to 29 is about twice as lon as on the other side from 30 to 31, but in iig. 4 the' corresponding closure from 26" to 29 is nearly three times as long as from 30 to 31. Moreover, this distortion of signals would be increased by the uncertainty as to the polnt of operation of the relay. Thus, if the contact broke at 33 instead of 32, the resulting signal received would be shortened to the time represented by30-31 which. is less than a third as long as from 26 to 29 whereas the signal should be half as long.

There is still another respect in which the disadvantage of the wave shape of' Fig. 4 becomes manifest compared Awith Fig. 3. The flexibility of the spring contact members '16 permits the end of the armature end of the larmature 25 may continue through several periods, but if a strong current is maintained in the coil 13, the contact will not be broken and there will be no chattering. This will be the manner of operation for the contact is made at the time indicated by the point 26, a strong holding current is maintained for as Amuch as seven or eight thousandths of a seconda During this time the oscillation of the armature is damped out by the type of contact springs employed. However, in Fig. 4 it will be seen that when the contact is made at 26', the current is already beginning to die down and a fluttering of the end of the armature may continue until the current becomes so weak that it will not hold the contactclosed, thus making it possible for a. certain amount of chattering, as at the point 35. If the dotted lines of armature travel 29 to 30 be assumed, it will be seen that closure is not effected until after the peak current is passed and the tendency for the armature flutter to ydevelop into contact chatteringwill be even more probable.

Since in long submarine cable systems the received current impulses are of the rounded Wave form, it is essential that a relay for use in such systems be capable of satisfactory operation on current impulses of that form. It therefore follows that the magnetic circuit of the relay must not only be very sensitive for operationLbut must eliminate so far as possible the eii'ect of residual magnetism which makes the operation of the relayv uncertain. The requirement of high sensitivity is particularly urgent in connection with a relay operated at high speeds since under such conditions it is necessary fo insure rapid travel of the armature, in order to obtain satisfactory closure of contacts vand only with a. relay of vhigh sensitivity is it possible to obtain suiiiciently rapid travel with the small currents available.

Although at irst glance it might seem that the residual effect of such a relay is due principally to the remanence of the material used, such is not the case,'due to the numerous gaps in the magnetic circuit andthe resulting demagnetizing effect of the poles at such gaps, but is due chiey to the coercive force or coercivity of the Ymaterial of which the magnetic circuit is composed'.

Silicon steel which has been largely used in relays heretofore not only is objectionable because of its comparative brittleness and the diiiiculty of working it, but also because it has a comparatively high coercive force. AI magnetic material known as permalloy when given a suitable heat treatment has been found to have a permeability at low magnetizing force greater than that of iron and a coercivity much below that of Fig. 3. It will be seen that afterE iron. `This material is described and claimed in patent to G. W. Elmen 1,586,884 issued June 1, 1926. Particularly good results were obtained in tests when employing a variety of permalloy prepared by fusing nickel and iron together in the proportion of 781/2 per cent nickel andQllg per cent iron, good commercial grades of these materials being suit-` able for this purpose. Good results may be obtained when the nickel content predominates'and the rest is iron or iron with small per cents of other elements which may be present as impurities or to increase the resistivity, as may be done for example by adding chromium. The fused composition is poured into a mold to bring it at once to the proper shape, or it may be brought to the desired shape after molding by bein hammered, swaged, drawn, rolled, or worke in any other simple manner. After being brought -to thel desired shape, the composition is given a hcat-treatment to develop thereinthe highest permeability possible at low magnetizing forces and the lowest possible coercive force. According to present practice, this is done by heating the desired shapes to a temperature of about 850o C., maintaining it at that temperature for a few minutes to insure a uniform temperature throughout, then cooling slowly to a temperature of about 600o C. which is just about the critical or transition temp-erature of the alloy, that is, the temperature at which the magnetic properties disappear on heating.

and reappear on cooling; and iinallylcooling from that temperature more rapidly but at adefinite rate dependent upon the ratio of nickel to iron in the alloy. A convenient method of securing the desired rate of cooling after the material has been maintained for a few minutes at a temperature of 850 C. has been found to be a rapid withdrawing of the material from the furnace and placing it in a blastof air which is controlled to secure a desired rate of cooling. The necessary cooling Will always be `at a rate inter mediate that required for annealing and that at which such strains would be set up in the material as to lower its permeability below the desired value. The results of tests on a relay of the 'type described in which'the magnetic circuit is composed of this variety of permalloy .as compared with the results of an exactly identical relay in which the armature is made from silicon steel and the pole pieces from a high grade of magnetic iron are shown on Fig. 5 ofthe drawing.

Curve A shows the contact pressures obnasdaq? yidentical with the relay of curve A in construction and adjustment. Curve A shows the residual effect or the contact pressure of the relay of curve A, immediately after the various operating currents had been removed. Curve B shows the residual coutact pressures for the relay of curve B in which the magnetic circuit is of permalloy. The contact pressures shown in curves A and B are due chiefly to the coercive forces ofthe materialsl used in the magnetic circuits although these pressures are, to a very slight degree, augmented as a result 0f the flux from the permanent magnet due to the armature being in its deflected position. The minimum direct current operating value of the relay employing a silicon steel armature and magnetic iron pole pieces was .O60 milliamperes as compared to a similaiminimum operating current for the nickel iron alloy of .032 milliamperes. For current values of the order of the minimum operating current, the relay having the nickel iron alloy magnetic circuit operates with a much higher contact pressure and therefore is more satisfactory and has less tendency to chatter. Although for operating currents above 'one milliampere. the contact pressure of the relay having the permalloy magnetic circuit is less,

4we are chiefiy concerned with the contact pressuresV at the minimum operating currents and for this reason the relay having the permalloy magnetic circuit is far superior.

In order to assure that this relay will operate satisfactorily under service conditions, it is necessary to determine the residual magnetism in the relay after operation with a maximum current which may be as high as l5 milliamperes. Referring to the curve, it will be noted that with the relay having the siliconV steel armature, the residual effect after heilig operated on a current of 15 milliamperes is approximately 4% grams whereas the residual pull under the same conditions for the permalloy relay is less than l@ gram. By thus reducing the residual effect, the operation of the relay is improved very materially and distortion of signals is overcome to a large extent.

In addition to the vadvantage accruing from higher permeability at low magnetizing forces and alowgr coercive force, the relay with permalloy is also quicker acting due to the low hysteresis loss of the material. The comparatively high hysteresis loss in an armature employing a material, such as magnetic iron or silicon steel, produces power losses which oppose the motion ofthe armature by reducing the iux density caused by a varying current, whereas in a relay employing an armature of permalloythe movement of the armature is less sluggish due to its low hysteresis loss and the relay therefore operates more satisfactorily on high speed telegraph systems.

Since, as already referred to, both the polarizing and operating fluxes reverse in the armature when the relay operates, the magnetic characteristics of the armature are of great importance. Then using permalloy for the armature and a high grade of magnetic iron for the other portions of the magnetic circuit the operation shows a decided improvement over that of a similar relay having a silicon steel armature although as would be eipected. the improvement is not as great as when the entire magnetic circuit is composed of the nickel iron,

alloy.

By the term low magnetizing force is meant a force of a few tenths of a gauss.

A particular type of sensitive relay having the improved magnetic circuit of this invention has been described above, butV the invention in' its broader aspects is not limited to any one type or form of relay being applicable wherever one or more of the advantages mentioned can be obtained.

What is claimed is:

l. An electromagnet device comprising an energizing coil, pole pieces therefor, an armature and a magnetic circuit including said armature and pole pieces composed of a material comprising nickel and iron of such low eoereivity that the armature operates at a precise current value substantially independent of its previous magnetic condition.

2. An electromagnet device comprising an energizing coil, pole pieces therefor, an armature and a magnetic circuit including said armature and pole pieces having a portion thereof composed of a nickel-iron alloy of such low eoereivity that the armature operates at a precise current value substantiallv independent of its previous magnetic condition.

3. An electromagnetic device comprising an energizing coil, pole pieces therefor. an armature, and a magnetic circuit including said armature and pole pieces having a portion thereof composed of a nickel-iron alloy of such low eoereivity that the armature is released at 'a precise current value substantially independent of the operating current value.

4. A relay to operate with precision of response at a definite input current consisting of an input winding, pole pieces therefor, relav contacts, and an armature controlling said contacts and actuated by flux developed in said pole pieces, the magnetic circuit comprising said core and armature having at least a considerable portion thereof composed of a nickel iron alloy with substantially lower eoereivity lthan iron, wherean energizing coil, pole pieces therefor, means for polarizing said pole pieces, a balanced magnetic circuit including said armature so arranged that both the polarizing flux and the flux produced by the energizing coil are reversed'in direction with movement of the armature, said armature being composed of a nickel iron alloy of such low coercivity that the armature is operated at a precise current value substantially independently of its earlier magnetic condition.A

6. An electromagnetic relay comprising an energlzlng coil, pole pleces therefor, an armature and a magnetic c1rcu1t includlng n said pole pieces and armature, composed of 'a material containing at least two members of 4the magnetic group of metals and having such low coercivity that the Contact pressure exerted by said armature due to residual magnetism is less than one fifth that under the same operating conditions in a similar relay having a silicon steel armature and pole pieces. f

7. A polar relay designed to operate on current receivedv over a high speed, long, loaded submarine telegraph cable comprising an armature, a coil for actuating said armature, and pole pieces completing a magnetic circuit through said armature, said armature and pole pieces being composed :of a nickel iron alloy having a coercivity less AUSTEN M. CURTIS. 4

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