US2689883A

US2689883A - Impulse-repeating electromagnetic relay

Info

Publication number: US2689883A
Application number: US250974A
Authority: US
Inventors: John I Bellamy
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; International Telephone and Telegraph Corp
Priority date: 1951-10-12
Filing date: 1951-10-12
Publication date: 1954-09-21
Anticipated expiration: 1971-09-21
Also published as: DE936218C; FR67801E; FR1068971A

Description

Sept. 21, 1954 J. l. BELLAMY 2,689,883

IMPULSE-REPEATING ELECTROMAGNETIC RELAY Filed Oct. 12, 1951 RIG. 1

44 45 43 4042 I 4| 25 9 37 47 33" i r al INVENTQR M a. WWW

Patented Sept. 21, 1954 IMPULSE-REPEATING ELECTROMAGNETIC RELAY John I. Bellamy, Wh-eaton, Ill., assignor, by mesne assignments, to International Telephone and Telegraph Corporation, a corporation of Maryland Application ctober12, 1951, Serial No. 250,974

4 Claims. 1 This invention relates to animpulse-repeating electromagnetic relay, and it primary object is to provide a relay of that kind which will respond with improved faithfulness over a Wide range of.

series and shunt resistance conditions of the signal line over which the impulses are received.

Thisapplication is a continuation in part of my prior application for Electromagnetic Relays, Serial Number 687,629, filed August 1, 1946.

GENERAL DESCRIPTION A simple, reliable, and economical form'of electromagnetic relay widely used in telephone switchboards and in related fields is based on a U-shaped magnet structure, made up. of an. L- shaped magnetic return plate and an electromagnet which lies parallel to the longer arm of the return plate, with one end secured to the shorter arm. An armature, mounted on the free end of the return plate and attractable to the electromagnet upon energization thereof, controls one or more sets of contact bladesmounted on the return plate.. Among other uses, such a relay is used as a. a line relay to repeat direct-current control impulses into local circuits.

Reference is made to Telephony, Including Automatic Switching, by Smith; Frederick. J. Drake and Co., 1924. Figure 203 of that publication. shows a line relay LR of a selector switch and of a connector switch controlled successively by series of impulses received over a line froma calling telephone. Adjustment of Automatic Apparatus, startin on page 3'71 of that publication, points outthatthe pulsing mechanism of the telephone calling device is adjusted to give a normal impulse speed (frequency) of about ten per second; that a ratio of'about 65 percent break of the impulse contacts is common; andthat, in one example, the extreme test limits of the line-resistance range over which a line relay can successfully repeat the impulses at a rate of fourteen per second (see paraditions, comprising, (1) a line of-minimum line resistance, but withpoor insulation and conseqnent high line leakage, and (2) a line of maximum line resistance, but with good insulation "and consequent low line leakage. As the noted Chapter XXIII; Testing and 'tacts.

publication makes clear, a line relay adjusted to meet both extremes operates early and restores late under the first extreme condition, while it operates late and restores early under the second extreme condition. On analysis, this appears to be the necessary consequence of a relay of the noted character, wherein the armature is acted upon by an electromagnet which supplies a variable operating force in but a single direction, and is opposed by the fixed restoring-spring load of the contact-blade assembly.

For the first noted extreme condition (a line of minimum series resistance and maximumleakage), the armature of a relay having a correct basic adjustment (armature stroke and residual air gap) requires a heavy restoring force to insure that it restores with reasonable promptness when the line is opened at the impulse con- The magnetic structure of the relay is then at its highest point of magnetic saturation, and thehigh magnetic energy tends to dissipate slowly because of the shading effect of the low shunt resistance. Moreover, eddy currents and the residual tendencies present in the magnetic structure tend to cause the armature of a highly saturated relay of this type to restore late unless the restoring spring force is substantial.

When the same relay, soadjusted and with the noted necessarily heavy restoring-spring load, is used for the second noted extreme condition (a line of maximum series resistance and negligible leakage), the armature restores more quickly because the flux level of the magnetic structure is, much lower. This action, coupled with the fact that the high series resistance causes the armature to operate much later on the closure of the impulse contacts, causes a very'large change in the break-make ratio of the repeated impulses. In practice, the restoring-spring force is so regulated that the departure from the most desirable-ratio is shared about equally between the two extremes of line conditions. Then the most desirable break-make ratio of the repeated pulsesoccurs when the connected line has a combination of series and shunt resistances falling about member in the form of a branch pole member having a shading device thereon. The branch pole member acts upon the armature in opposition to the normal tractive pole member, whereby the armature is operated by the main, unshaded pole member at the beginning of an impulse, and restored by the action of the auxiliary, shaded pole member at the termination thereof. By this arrangement, (1) the range of line conditions over which the relay can repeat impulses of tolerable ratio is increased, and (2) the impulses repeated by the relay over the extreme range of known relays are of a comparatively uniform break-make ratio.

Other objects and features will appear as the description progresses.

The drawings Referring now to the drawings, comprising Figs. 1 to 6,

Figs. 1 to 3 show respectively a side, top, and front view of relay RI, comprising the preferred embodiment;

Fig. 4 shows a partial side view of relay R2, comprising a desirable modification of relay RI of Figs. 1 to 3;

Fig. 5 shows a typical circuit use of relay R| (Figs. 1 to 3); and

Fig. 6 shows a modification of Fig. 5 which uses relay R2 (Fig. 4).

Preferred embodiment (Figs. 1 to 3) Referring now to Figs. 1 to 3, relay RI, the preferred embodiment, includes an L-shaped magnetic return plate 2, having the core 6 of the electromagnet fixed thereto by screw 1. Spoolheads 1 and 9 are fixed with core 3 to define a space for windings 3, separated by washer 50. Four winding terminals I!) are fixed with spoolhead 9. The spoolheads ii and 9 are preferably of a similar half-circular and half-square shape, as shown for the spoolhead 8 in Fig. 3. The circular half of spoolhead 9 is uppermost, While the square half of spoolhead 8 is uppermost, providing a sturdy surface which rigidly supports the front end of member 2 and holds the electromagnet against rotation.

Armature 5 is supported on pivot rod I8, which passes through ears 2| of the armature and ears ll of bracket [5, secured to member 2 by screws H5. Bracket I5 is preferably of magnetic ma terial to provide a comparatively large area of return air gap between armature 5 and part l5, and thence through member 2. Strip IQ, of nonmagnetic material, is secured to part l5, as by rivets 20, to act as a front stop for armature 5 in its forward motion toward the main, tractive pole member 4.

The contact mechanism of the relay is contained in assembly of Figs. 1 and 2, including clamp plates 34 and 43, secured together by clamp screws 44, and retained on member 2 by screws 45.

The contact assembly includes two columns, 3| and 32, of contact blades. Each column includes a lower fixed contact blade 31, an intermediate, traveling contact blade 39, and an upper, fixed contact blade 4 The

fixed contact blades

31 and 4| are preferably of substantially greater thickness than the traveling contact blade 39, the thickness of which is accentuated in the drawing to avoid crowding of the lines.

Actuation of the contact mechanism is accomplished by the T-shaped rear arm 22 of the armature 5, through the medium of the relatively 4. thin actuating blade 35 and the overlying insulating actuator 41.

The fixed contact blades 3'! and 4| are each provided with windows 48 (Fig. 2), to permit actuator 41 to move freely therethrough. Each contact blade has a rear terminal portion 33 for the attachment of a conductor thereto. The contact blades are maintained insulated from each other and from the clamp plates 34 and 43 by insulating plates 36, 38, 40, and 42.

The normal position of armature 5 is determined by back-stop arm 23, which rests on the nonmagnetic plate 25, retained in position beneath the assembly 3!).

Bending of actuating arm 22 of the armature to bring the movable contact elements to the desired position (with armature 5 fully operated and resting against stop member I3) as well as the bending of back-stop arm 23 to determine the normal position of armature 5, is facilitated by slots 24 through the

arms

22 and 23 for receiving a suitable adjustment tool.

Movement of armature 5 responsive to energization and deenergization of the windings 3 is controlled jointly by the main, actuating pole member 4 and the auxiliary, restoring pole member 5|. Member 5| is encircled by a conducting shading device 52, composed of a desired number of laminations of a conducting material such as copper.

Pole members

4 and 5| are secured to the front end of core 6 by screw II, which passes through enlarged or vertically slotted openings in

parts

4 and 5| to permit vertical adjustment of these i parts before the final tightening of screw II.

For most uses of the relay, the tractive face of pole member 4 is a substantial distance below the upper face of front stop member Is, to leave a substantial residual air gap between

parts

4 and 5 with the armature 5 in its operated position, and part 5| is suiliciently high that about the same air gap normally exists betwen it and the upper surface of armature 5. It will be understood that armature 5 is maintained in that position in the illustrated embodiment by the relatively light spring load imposed by parts 39 and 35.

When a substantial current flow occurs in windings 3,

pole members

4 and 5| are both magnetized and each attracts armature 5. Conducting shading member 52, however, delays the passage of flux through member 5|, with the result that armature 5 is effectively attracted by member 4 and moves to operated position against the upper-face of stop-member l9 before the flux through pole member 5| can reach an effective restraining value. Incidental to this armature movement, actuating arm 22 raises actuating spring members 35 to thereby raise actuators 41. Contact blade 3| of each column (3|, 32) is thereby lifted out of engagement with its fixed contact member 31, and is brought into effective engagement with its fixed contact member 4|.

When the current flow through the windings 3 is subsequently terminated,

pole members

4 and 5| are consequently demagnetized, but the demagnetization of pole member 5| is delayed by the shading action of member 52, with the result that armature 5 is thereby attracted to its illustrated restored position, in aid of the restoring force exerted by spring members 35 and 39.

Reversed-action embodiment (Fig. 4)

Referring now to Fig. 4, the relay R2 shown therein is exactly similar to the relay RI of Figs. 1 to 3 except that Shading member 52 has been shifted from restoring pole member I to actuating pole member 4.

When the windings 3 of relay R2 are energized to magnetize pole members 4 and 5I, member 5| becomes magnetized immediately, while the passage of flux through pole member 4 is delayed by the action of the conducting shading member 52. As a result, armature 5 remains in normal position.

When the current flow through the windings of relay R2 is discontinued, pole member 5I demagnetizes with comparative promptness, while shading member 52 delays the demagnetization of pole member 4 for an interval. During this interval, armature 5 is operated by member 4. If the windings remain currentless until the effect of shading member 52 has died away, armature 5 is then restored by spring action.

In the normal intended use of relay R2, hereinafter described, the establishment of current flow through the windings of the relay is followed by a series of impulses in the form of momentary current interruptions. As a consequence, the armature of the relay is attracted to pole member 4 upon the first interruption and remains so attracted until the current flow is resumed, whereupon it is magnetically restored by the overpowering action of pole member 5|, remaining thus restored until the next interruption occurs.

Circuit use of relay R1 (Fig. 5)

Referring now to Fig. 5, a simplified typical contemplated use of the relay R! of Figs. 1 to 3 will be described.

506 represents the control station, which may comprise a dial telephone, with 5") representing the normally open hookswitch contacts and 5 representing the impulse contacts of the dial calling device. Conductors 5I2 are the usual line conductors in a two-wire signalling system, such as the conductors of a dial telephone line. LS represents a partially illustrated line switch of the type indicated in Fig. 203 (opposite page 268) of the cited publication, the arrangement being such that any one of a number of lines such as 5I2 can be switched into connection with the relay RI. Each lineswitch LS may have access to a number of the digit recording circuits, and each such circuit may be accessible to a number of lineswitches LS. The symbols 5 I I indicate multiple connections to the contact banks of other lineswitches LS.

Relay RI (of Figs. 1 to 3) cooperates with the associated hold relay 52I in controlling a stepping switch SSI. In a dial telephone system, the stepping switch is used to extend the conductors of a calling line to, or toward, the conductors of a called line, but for simplicity of disclosure the switch SS is illustrated as controlling the lighting of display lamps 550.

Stepping switch SS includes a brush 521 having the illustrated normal position and having ten oif-normal positions in which it engages its associated contacts 1 to 1c respectively.

It is advanced by stepping magnet 523, and is returned to normal by the usual restoring spring (not shown) upon the operation of release magnet 526.

Station 500 may be at some distance from the apparatus controlled therefrom, or it may be a station comparatively close to the apparatus. The resistors 5I3 and 5M represent the distributed wire resistance of the line 5I2, and resistors 5I5 and 5 I 6 represent distributed leakage between the wires of the line, such as may result from wet, broken, or missing insulators; contact between bare line wires and tree branches; or moisture in a cable.

Parts 8, fl, and 22 may each have a 1-inch width; core 6 may be three eighths inch in diameter; and the other parts may be generally in proportion according to the scale used in the drawing. With this proportioning, each of the windings 3 may comprise about 4000 turns of No. 34 enameled copper wire, having a resistance of approximately 200 ohms. With a battery of about 50 volts, such as is commonly used in the central exchange of a dial telephone system, the relay RI has been found to repeat dial impulses satisfactorily, without change of adjustment, over lines 5I2 ranging from substantially zero to 1800 ohms series resistance, represented by resistors 5I3 and 5M on the drawing, and with leakage (shunt resistance) ranging between infinity and 3600 ohms, represented by resistors 5 I 5 and SIB.

Operation of Fig. 5

When digit information is to be transmitted from station 500 of Fig. 5, hookswitch contacts 5H3 are first closed; impulse sending contacts 5I I are then caused to open momentaril a number of times to deliver a series of break impulses over the line M2; and hookswitch contacts {Sill are later opened when the transmitted registration is to be cleared out.

Upon the closin of hookswitch contacts 5I0, and if the lineswitch LS is controlled as is the one shown in Figure 283 of the cited publication, the usual operations of switch LS occur to extend the calling line 5I2 to an idle circuit such as the one illustrated. Ehereupon, the two windings 3 of line relay RI are energized in series over line 5I2, by current supplied from the ungrounded negative pole of a grounded current source (not shown) assumed to be of approximately 50 volts in accordance with the usual signalling and dial-telephone practice.

As the current rises in the windings 3 of relay RI, there is an in-phase rise of flux through pole member 4 of Fig. 1, and a much slower rise of flux through pole member 5! because of the retarding action of shading member 572. As a consequence, a greater tractive force is exerted on armature 5 by the pole member 2 than is then exerted by the shaded pole member 5i. Armature 5 therefore moves promptly into engagement with its front-stop member It, being then nearer to member 4 than to member 5|. By the armature movement, contact blade I9 is moved away from member 31 and into engagement with member 4 I, as previously described. The engagement of parts 39 and EI closes a circuit for hold relay 52 I, which relay thereupon operates. At its contact arm 528, it disconnects contact member 3? from the release wire 524 and connects it to the stepping wire 522, in preparation for transmission of impulses to stepping magnet 523.

On each momentary interruption of the line current incident to the noted operation of impulse-sending contacts EI I (as upon the restoration of the usual telephone calling dial) armature 5 of the relay RI is promptly restored, the action being enhanced, as previously noted, by the prompt cessation of flux in pole member 5 as compared to the flux in pole member 5!, which persists by virtue of the retarding action of shading member 52.

At the end of each momentary interruption impulse, the resumption of normal current flow 7 through thewindings 3 of relay RI causes armature 5. of the relayto reoperate as described for the initial closure of the line circuit.

On each restoration of relay RI, the circuit of hold relay 52! is opened at

contact blades

39 and 4!, but relay 52! remains operated during the series of impulses because of its slow-releasing, as by having the indicated copper sleeve surrounding its core, between the core and the winding, as is commonpractice in the art. As a result, relay 52 I remains operated continuously throughout the transmission of a series of impulses.

On each momentary restoration of line relay RI, with hold relay 52! remaining operated, an impulse of current is transmitted to stepping magnet 523 over wire 522, through

contact members

39 and 31, and the front contact of member 528. Stepping magnet 523 responds by advancing wiper 52! one step for each impulse received, engaging a separate one of itscontacts 1 to 10 on each step. Since wiper 52'! is grounded, the lamps 1 to 10 in group 550 are momentarily lighted successively during the receipt of impulses. The lamp which corresponds to the contact on which member 52'! stands at the end of the series of, impulses remains lighted as a display signal of the value of the digit transmitted and registered.

Off-normal contacts 525 become closed on the firststep of wiper 521.

When the registration is to be cleared out, hookswitch contacts 5 I are again opened and are allowed to remain open. When this occurs, line relay RI restores and remains restored, hold relay 52 I restoring shortly thereafter.

During the interval required for relay. 52! to restore following the restoration of relay RI, an additional, and somewhat prolonged, impulse is transmitted over wire 522 to stepping magnet 523. Wiper 52! is thereby advanced to the next contact, extinguishing the lamp previously lit as a display signal, and lighting the next succeeding lamp. If desired, this action can be avoided by adding one or more control relays, as is done in the signalling art.

When hold relay 52! restores, the circuit of stepping magnet 523 is opened, and a circuit is closed for release magnet 52%, from ground at contact blade 39, through contact blade 37, back contact 528, and oiT-normal contacts 525. Theresulting operation of release magnet 526 causes brush 521 to be restored to its illustrated normal condition. Off-normal contacts 525 now open the circuit of release magnet 526, leaving the circuit of Fig. in its illustrated normal condition.

Reversed-action embodiment (Figs. 4 and 6) Referring now to Fig. 6, the use of the reversedaction relay R2 of Fig. 4 in a typical circuit arrangement will be described.

Fig. 6 is like Fig. 5 except that relay R2 is substituted for relay RI, and the associated control circuit is revised accordingly. Relay R2, because of its described reversed action, does not require a normally closed contactmember such as 3'! of Fig. 5. Instead, it uses two pairs of normally

open contact members

39 and 4!, termed 39R, MR, and 39L, 4|L in the respective columns 3! and 32 of Fig. 2.

Upon the closure of a circuit for relay R2, as over the line 5 I 2 of 5, the current builds up in the windings 3 of relay R2, but no movement of the armature (5) thereof occurs for reasons herebefore given, wherefore the contact members of the relay remain in their illustrated normal open condition.

Upon each momentary interruption of the line, as at impulse contacts 5! I, the resulting cessation of current flow in the windings 3 of the relay R2 causes the armature (5) to be operated by the delayed action of pole member 4, bringing the The armature of relay R2 comes to rest in its illustrated restored condition when the line remains closed at the end of the transmission of the series of interruptions impulses, leaving the contact members of Fig. 6 in their illustrated open condition.

Upon each noted momentary closure of the contactmembers of relay R2, a circuit is momentarily closed by

contacts

39R and 4 IR, over impulse wire 622, through contacts 628, for stepping magnet 623. By the action of magnet 623, wiper 62'! is advanced step-by-step over its associated contacts to light a desired lamp 650.

As a further result of each momentary closure of the contacts of relay R2, contacts 3.9L and 4 IL close a circuit over wire 624 for release magnet 526. Release magnet 526, as is indicated by the notation "S. 0., is a slow-operating electromagnet, preferably being so arranged by having a winding of considerable inductance and having the usual armature-restoring spring (not shown) adjusted to apply substantial restraining tension. As a consequence, release magnet 626 does not respond to any of the momentary impulses delivered to it along with, and incidental to, the noted delivery of stepping impulses to magnet 623.

When the, display lighting of one of the lamps 1 to 10 in group 550 has served its purpose, the opening of the calling line, as at hookswitch contacts 5H3, causes a cessation of line current. Thereupon relay R2 is operated to close its contact members as previously explained. Since the. line current is not resumed at this time, armature 5 soon restores, at the end of asubstantial fraction of a second for example.

During the interval when relay R2 is operated following the notedopening of the calling line,

release magnet 625 operates because the length of the impulse then deliveredthereto over wire 624 exceeds the slow-operate period of the magnet. Upon operating magnet 626open-circuits stepping magnet 623 at its contacts 628. Magnet 626 remains operated, and wiper 621 is thereby restored to its illustrated normal position. Release magnet 626 soon becomes deenergized, upon the previously noted restoration of relay R2 when. the current in shading member 52 of'Fig. 4 diesout. The apparatus of Fig. 6 is thus again in its illustrated normalcondition.

Performance considerations the design-o1" the relay and the adjustment thereof.

One important design consideration is armature lightness. The armature should be relativelylight (having a small effective mass, or-

moment of inertia) compared to the available operating force, whereby that force provides a high acceleration according to the general formula that acceleration equals the force divided by the mass (A= /M). Then, the movement of the armature from either of its stop positions to the other can occur readily within the short interval allowable for such movement. In this respect, the armature 'can very likely be improved by narrowing its width forward of the screws [6 (see Fig. 2), and by correspondingly narrowing the width of pole members :3 and iii, accompanied if necessary by an increase in the thickness of the pole members. Lightness of armature 5 is further promoted by constructing it of a magnetic material having maximum permeability and having a high saturation value, whereby its cross-sectional area can be correspondingly reduced.

In the illustrated embodiment, however, the armature 5 has not been specially shaped for maximum lightness, nor has the use of a magnetic material better than commercially available annealed ingot iron sheet (about one sixteenth inch thickness) been found necessary for the successful use of the relay under the conditions hereinbefore described. Annealed ingot iron is satisfactory for the remaining magnetic items, and soft cold-rolled steel has been used successfully for these items. Whatever the arma ture shape or material, best results are obtained when the armature itself comprises the most restricted portion (highest reluctance per 'unit length) of the magnetic circuit, and comprises the portion of the circuit which first reaches saturation when the windings 3 develop sufficient magneto-motive force.

For the most favorable response over a given range of operating conditions, the armature should have a short stroke. That is, the relay should be so adjusted that the normal position and the operated position of armature 5 are as close together as the demands of the contact members (Bl, 39, M) reasonably permit. This arises from the fact that the joint control exercised by the pole members 4 and El (in operating the armature 5 positively in each of the two directions of movement as the force differential shifts in direction) is best exercised when the armature is never so much closer to one pole member than to the other that the nearer pole unduy restrains the armature from starting its travel toward the distant pole. In all forms of the device which applicant has constructed and tested, the operating range is very limited if the stop positions are such that the armature comes into contact with either pole member, and particularly the unshaded pole member. With the armature contacting a pole member, it is very difficult to adjust the device so that the armature will move to the other pole member unless the pole members are brought much closer together than the drawings indicate. The armature stroke then becomes so small that the resulting movement is less than the requirements of the illustrated type of contact members.

The shading efjectiveness of shading member 52 may vary between rather wide limits, such from 506 to lGGU mhos for the circuit use illus trated in Figures 5 and 6. Considerably higher conductance valuesof the shading device can be used for interruption impulses of ten per second, so long as the line current and the flux through the shaded pole member have both reached substantially a steady-state condition before the starts, and for low-frequency interruption-im pulse situations wherein the initial interruption closely follows the initial line closure, best results are obtained with the illustrated structure when the conductance of shading member 52 does not exceed 500 mhos. Under the noted circumstance, of only a very fleeting impulse, the passage of flux through the shaded pole member is so retarded by a shading device of high conductance that the energy stored in the shaded pole member is insufficient to cause the armature to be urged toward that pole member with suflicient vigor when the current flow in interrupted.

Applicant is aware that certain prior structures, including the disclosures in certain references of record in his prior patent application hereinbefore identified, have employed an armature controlled jointly by an unshaded pole member and an opposed shaded pole member, but no such prior structure, so far as applicant is aware, is capable of attracting its armature in one direction from a first position to a second position responsive to each flow (or sharp rise) of direct current, and of attracting the armature back to its first position responsive to each cessation (or sharp drop) in direct current. In making the foregoing statement, applicant takes the position that any half cycle of alternating current, considered alone, comprises a direct-current impulse that rises to full value and ceases during the period of the half cycle of current.

The several factors governing the ability of a structure of the disclosed character to operate the armature as hereinbefore described includ the following:

1. Armature lightness and bias, which govern the ease with which the net magneto-tractive force, available incidental to a rise or a fall in current, can move the armature from its presently occupied position to its other position;

2. Armature sensitivity to flux differential, which is governed by the distance by which the armature in either stop position, is separated from the nearer tractive pole face as compared to its distance of separation from the other tractive pole face;

3. Total flux range, which is limited by the amount of flux which substantially saturates the structure; and

4. Amount of shading or the conductance of shading member, which determines, for any rate of change of total flux, the distribution of such rate of change between the two pole members.

When a device of the disclosed-character has the foregoing factors favorably related according to the description hereinbefore given, it operates in the described useful manner. Eut, when one or more of the factors is too far out of proportion with the others, the device cannot perform according to the invention. For example, if the shading conductance is too low compared to the flux range and to the armature lightness and sensitivity, the armature cannot change positions responsive to any single impulse of direct current, or half cycle of alternating current, of any strength or sharpness of rise or fall. If the rise or fall be comparatively gradual, then the flux change is gradual, and the flux differential. is insufficient to generate a net force differential great enough to withdraw the armature from its nearer pole member. On the other hand, if the rise or fall of current be abrupt, the flux. change is abrupt, but its duration and range are so cur-- tailed by the flux range of the structure, that any resulting net magneto-tractive force is too fleeting to attract the armature away from the nearer pole and move it-to its stop position closer to the other pole. On repeated tests, a device so misproport'ioned responded to 60-cyc1e alternating current even though it would not respond toany direct-current pulses oi any magnitude or rate of change. A partial explanation seems to reside in the fact that the first portion of any half cycle of an established alternating current erases the residual magnetism left in the structure by the preceding half cycle, leaving the structure momentarily demagnetized. It was also noted that the armature, while humming or buzzing because of its relative lightness, stayed at or near the unshaded pole, and did not approach the shaded pole. When a sufiiciently large restoring spring tension was applied to cause the armature to approach the shaded pole, it remained there continuously, giving no response to the alternating current. It was further o'bserved that lower frequencies of alternating: current had no more effect on the device in question than direct-current pulses all of one polarity.

I claim:

1. In a quick-acting impulse responsive device, a relatively light armature and means rendering it reciprocable between two' positions", an electromagnet for operating the armature, pole means forone pole of the electromagnet divided into two branches ending in pole faces so disposed as to exert opposite tractive forces on the armature in directions toward. the two armature positions respectively-shading means for one branch delaying flux change therein with respect to flux change in the other branch incident to the rise and to thefall of current in the winding of the electromagnet responsive to the application and termination of an impulse of direct current to the winding, means included in the said parts and means for rendering the transient resultant of'the opposite tractive forces capable of moving the armature from one of its positions to the other responsive to each said rise of current in a series, and rendering it capable of moving the armature back to its said one position responsive to each said fall of current of the series.

2. In a quick-acting impulse-responsive device as set forth in claim 1, means biasing'the armature to move to one of its positions when magnetically free to do" so, said transient resultant forc "hen in one direction acting with the biasl 2 ing means to move the armature to its last said position, the said transient resultant force when in the other direction acting against the biasing means to move the armature to its opposite position.

3. In a signal system, impulse-responding means for responding individually to the impulses of series of direct current impulses received over a pulse-transmission line, said impulse-responding means comprising an electromagnet having a winding connected in series with said line, an armature operatively associated with the electromagnet, means defining a first position and a second position for the armature, the electromagnet having a main pole member having a pole face so related to the armature as to attract the armature to its second position responsive to each of said impulses of a series, and means for restoring said armature from its second position to its first position responsive to the cessation of each of the impulses, said restoring means including an auxiliary pole member comprising a branch of the main pole member and having a pole faceso related to the armature as to attract it in opposition to the main pole member,v and a conducting shading member surrounding the auxiliary pole member and delaying flux change therein with respect to flux change in the main pole member, and means included inthe foregoing whereby the effect of. the restoring means is prevented from reaching full value on the receipt of an impulse until after the armature has movedfrom its first position toward its second position, and means included in the foregoing whereby the effector the restoring means is continued beyond the end oi. the received impulse to restore the armature from its second position to its first position.

4.. In a. signal system according to claim 3, means for applying a biasing force to move the armature to one of its positions when it is mag netically free, the impulse-controlled movement of the armature to its said one position being aidedv by said biasing force, and the impulsecontrolled movement of the armature to its other position occurring. against said biasing force.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 863,667 Struble Aug. 20, 1907 1,158,898 Conrad Nov. 2, 1915 1,421,269 Lucas June 27', 1922 2,513,400 Carson et al July 4, 1950