US2074584A - Electroresponsive device - Google Patents

Description

March 23, 1937. H Q GRAVS, JR I 2,074,584

ELECTRORESPONS IVE DEVICE File@ April e, 1954 4 sheets-sheet 1 v ATTORNEY.

March 23, 19370 H. c. GRAVES, JR 2,074,584

ELECTRORESPONSIVE DEVICE 4 Sheets-Sheenl 2 Filed April 6, 1934 INVENTOR.

BY @MAL j. @om

75l ATTORNEY.

March 23, H Q GRAVESy JR ELEcTRoREsPoNsIvE DEVICE Filed April 6, 1934 4 Sheets-Sheet 3 INVENTOR.

March 23, 1937. H. C, GRAVES, JR 2,074,584

ELECTRORESPONS IVE DEVICE Filed April 6, 1934 4 Sheets-Sheet 4 INVENTOR.

BY @Ma-d @om d ATTORNEY.

Patented Mar. 23, 1937 UNITED STTES OFFIC ELECTRRESPNSIWE DEVJIGE ration of New `Hersey Application April 6, 1934i, Serial No. 719,327

32 Claims.

My invention relates to electroresponsive devices and, while the devices of my invention are of general application in the control of electric circuits, systems and devices, they are particularly suitable for effecting the tripping of automatic circuit breakers.

More specifically, my invention is directed to electroresponsive devices which, when associated with an electric control circuit or system, will substantially instantaneously eect a controlling operation in response to excessive or severe abnormal circuit conditions as, for exam ple, overloads occasioned by short circuits, and which will, in addition, effect a similar control` ling operation upon the occurrence of moderate abnormal circuit conditions obtaining for a predetermined time. Preferably, the time delay in the second-named operation is roughly dependent upon the time-intensity characteristic of the abnormal circuit condition, For example, the device may operate within a predetermined time interval in response to moderate overloads, and after only a. slightly shorter interval upon the occurrence of heavier, but less than the aforesaid excessive, overloads such as may be occasioned by motor-starting operations.

In accordance with one embodiment of my invention, an electroresponsive device suitable for controlling, either directly or indirectly, an electric circuit, system or device, comprises a conventional electromagnet with a movable armature biased to a normal position and movable, in response to energization of the electromagnet, to an operative position. The armature is additionally biased to its normal position by a movable member andLor an additional biasing spring for increasing the energization of the electromagnet required to move the armature to its operative position. Means `are provided normally interconnecting the armature and the additional biasing means. When the energization of the electromagnet attains this increased magnitude, due to short circuits or severe abnormal conditions on the controlled circuit, the armature and its associated biasing means are substantially instantaneously moved to operative position.

There is provided also additional means responsive to moderate abnormal circuit conditions and effective after a time delay to release the additional biasing means, whereupon only the normal biasing force acts upon the movable armature, and such moderate abnormal conditions effect its movement to its operative position. This time delay means preferably com- (Cl. 20h- 88) prises a thermal element and a separate heater therefor, heated in accordance with the energization of the electromagnet, as by inductively coupling the heater or its circuit with the core structure thereof. The time constants of 5 the device under different magnitudes of abnormal conditions may be modled by proportioning the magnetic core structure to saturate under certain conditions, this saturation being effective also to protect the thermal element from excessive heating or electrodynamic strains or distortion.

Both the instantaneous operation of the device, in response to excessive overloads, and the time delay operation, in response to moderate overloads, are independently adjustable. If desired, a suitable indicating scale and pointer may be associated with the adjustable connection between the thermal element and the armaturev latch to indicate the time delay for which the device is adjusted. This indicating means may also be adjustable to compensate for variations in ambient temperature.

For a better understanding of my invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and 'its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 is a view in front elevation of a three-pole automatic circuit breaker controlledby an electroresponsive device embodying my invention, while Fig. 2 is a view in side elevation of the apparatus of Fig. 1;

Fig, 3 is a view in side elevation of an electroresponsive device embodying my invention;

Figs. 4, 5 and 6 are detailed perspectives of certain of the operating elements of Fig. 3; I

Fig. 7 is an exploded view of the member ino terconnecting the thermal element and the armature latch, together with the associated indicating scale and pointer;

Figs. 8 and 9 are perspectives of the thermal element heater alone and in association with the thermal element, respectively;

Fig. 10 is a perspective of the adjustable latchreleasing link, while Fig. 11 is a cross-sectional view showing the manner of engagement of this link with the thermal operating member;

Figs. 12 and 13 are perspectives of a modied form of thermal element heater and of such a heater associated with the thermal element, respectively; while Fig. 14 is a schematic diagram of the essential elements of my improved electroresponsive device, together with their circuit connections to an automatic circuit breaker; and

Fig. 14a is a schematic diagram of certain elements of my invention applied to a direct current circuit breaker.

Referring now more particularly to Figs. 1 and 2 of the drawings, there is shown a 3-pole automatic circuit breaker, of a conventional type,

comprising a base or panel member III and three movable contact assemblies Il, one for each pole of the breaker, cooperating with suitable stationary contact structure mounted on the panel I0. The movable contact assemblies I| may be operated to circuit-closing position by any suitable automatic or manual closing mechanism, although I have illustrated, by way of example, an operating handle I2 and suitable linkage mechanism I3 including a common operating member I4 which may be interconnected with the handle I2 by the latch |5, and which may be secured in circuit-closed position by operating the links I 3| 4 to an overcenter position. The latch I5 may be released by a pivotally mounted trigger arm I6 disposed to be operated by any of the three electroresponsive devices I1, each associated with, and connected in circuit with, one pole of the automatic circuit breaker. The electroresponsive devices are effective, also, to break the several toggles |3-I4 under certain conditions as described more fully hereinafter.

The structural'features of the electroresponsive devices are shown more clearly in Fig. 3 et seq. l

Referring to Fig. 3, it will be seen that th device comprises a magnetic core structure |8 secured to a panel or base member I9 and provided with a suitable energizing coil 2|). The magnetic circuit of the core structure I8 is open at one side, and cooperating with this open portion of the circuit, or air gap, is an armature 2| journalled on a pivot 25 supported from the base or panel |9. To prevent chattering of the armature at the pivot 25, it is provided with a detent 22 resting on a knife edge or other suitable pivot 23 spring supported from a bracket 23a secured to the base I9 and maintaining the pivoted end of the armature in its attracted position and in rm engagement with the pivot 25.

The armature 2| is biased to the position shown in Fig. 3 by its own Weight and/or by additional biasing springs, if required.

Under normal operating conditions, the armature 2| is restrained by additional biasing means comprising a carriage or roughly U-shapcd bracket 24 pivoted on base I9 at 25 substantially coaxial with the pivot of the armature 2|. The carriage 24 is connected with the armature 2| through a latch 26 which is provided with a detent engaging a spring extension 2|a of the armature 2|, adjustable as by a thumb screw 2 lb.

The latch 26 is pivotally mounted in the outer end of the carriage 24, as at 29, and is biased into engagement with the extension 2|a by a spring 21 attached to an arm 28 of the latch 26. The details of the latch 26 may be seen clearly in Fig. 5. The Wedge shaped detent of the latch 26 and the spring 21 ensure a rm engagement between the upper detent surface 26h and the upper surface of the armature extension 2|a. The carriage 24 is provided with an upwardlyr projecting member 24a, Fig. 4, which may be a block of insulating material, and which forms a stop to limit the downward motion of the armature 2|. The armature 2| is normally raised 'from the stop 24a, however, by the wedging action of the latch detent, described above. The weight of the lcarriage 24 may be suiiicient to provide adequate additional bias or, in certain instances, it may be desirable to provide also an additional biasing spring 30 which interconnects a projection 3| of the carriage 24 and a member 32 threaded upon an adjusting screw 33 supported in a bracket 34 secured to the base I9. By adjusting the screw 34, the member 32 may be moved upwardly or downwardly, changing the lever arm of the biasing spring 3D about the pivot 25 of the carriage 24 and thus varying the eff-ec- `tive biasing force.

.projection 26a of the latch 26, and cooperates therewith to release the latch upon a predetermined movement thereof. When the armature 2| is so moved to its operative position, it may directly eiect the opening or closing of cooperating contacts or, as illustrated, it may strike a tripping rod 38 sliding in a suitable recess formed in the magnetic core I8, which, in turn, releases the latch I5 and breaks the toggle I3-I4 to permit the opening of the breaker contacts.

'Ihe time delay operation of the device in response to moderate overloads is obtained by means of a bimetallic thermal element 39 and its associated heater element 40, the latter comprising a closed conductive loop, substantially rectangular in form, surrounding the magnetic core member I8 and inductively heated in accordance with the energization of the coil 20. The heater element has preferably substantially a plane surface and may conveniently be a sheet metal punching. The thermal element 39 and the heater 40 are supported, in intimate contact, at their upper ends by means of spring-biased screws 40e. Preferably, the thermal element is firmly secured to the supporting insulating block 40d by shoulders on the screws 40e which pass through openings in the heater element 48. 'Ihis latter element is resiliently held in intimate contact with the thermal element 39 by the springs 40e surrounding the shoulders of the screws 40e.

The configuration of the thermal element 39 and heater element 40 may be seen more clearly by reference to Figs. 8 and 9. As shown in these gures, the thermal element 39 comprises a pair of bimetallic strips 39a and 39h substantially parallel to and in intimate contact with the outside arms 480, and 40h, respectively, of the heater element 48, and secured in intimate contact 'therewith by means of the spring-biased screws 40e. The lower free ends of the bimetallic strips 39a and 39h are interconnected by an operating strip or member 39e. The operating member 39e has an opening 39d in which is inserted one end of an operating rod 4| secured therein by a spring-pressed washer 4|c, the rod 4| being provided with a shoulder 4|a, abutting against the member 39e.

A portion of the rod 4| is formed with a spiral thread 4 Ib with which engages an operating link 42, the details of which are shown more .clearly in Figs. 10 and 11. As shown in these figures, the link 42 is provided with upstanding projections or lugs 42a and 42h of such conguration as to be threaded upon the rod 4|. The link 42 hasan opening or bore 42c disposed to engage and slide along the unthreaded portion of the rod 4|. The link 42 has also an extending proo jection 42d engaging a slot 43 in a side plate 44 which may form a part of the enclosing and protective housing of the device. It will be clear that, by rotation of the rod 4|, the link 42 will be moved longitudinally by its threaded engagelU ment, rotation about the rod 4| being prevented by the projection 42d sliding in the slot 43. The link 42 is provided also with a longitudinallyextending projection 42e disposed to strike and disengage the latch 26 upon a predetermined deection of the thermal element 39.

In order to vary the time delay in the operation of the thermal element and to compensate for variations in the ambient temperature, there is provided an adjustment for the operating link 42 shown in exploded view in Fig. '7. As there shown, an adjusting knob 45 cooperates with a member 46 having a central bore through which the unthreaded portion of the rod 4| freely slides. A pair of screws 41 are effective to secure a rm engagement between the members 45 and 46 between which are clamped an indicating dial or plate 48 and an index plate 49. The rod 4| is provided with one or more flats or non-circular surfaces at' its outer end 4|d which engage a similarly formed opening 49a in the index plate 49. The index plate 49 has a plurality of circumferentially-disposed openings 49h which cooperate with a spring-pressed index button 56a secured to the bracket 36 as by a plate 56. As indicated in Fig. 3, the knob 45 is provided with a recess 45a into and out of which the end Md of the rod 4| freely moves. The indicating dial or scale plate 48 may be provided with a projection 48a cooperating with a fixed stop 5| to limit the adjustment of the thermal element and operating as an index pointer for the scale dial 48.

In Figs. 12 and 13 are illustrated modied forms of the thermal heater, designated as alone and assembled with the thermal element 39. In this modied construction, the members 40a' and 49h' are bent into'angles in which are disposed the bimetallic elements 39a and 39h,

while the cross members of the element 40 are offset from the plane of the thermal element 39.'

By this means, a better thermal relation is secured between the heater element 4D and the thermal element 39.

In Fig. 14 is shown schematically the essential operating elements of my improved electroresponsive device, together with a circuit diagram of the connections when applied to an automatic circuit breaker, as shown in Figs. 1 and 2. From this diagram it will be seen that the coil 26 is connected directly in series with the contacts of so the circuit breaker and thus is in series with the controlled circuit.

The heater element 46 is shown as its electrical equivalent of a resistance 52 connected in circuit with a coil 53 inductively coupled to the u.; coil 26 by the magnetic core i8. The other elements are shown schematically substantially in the operative relationship of Fig. 3.

The operation of the above-described electroresponsive device will be best understood by 7o reference to Figs. 3 and 14. If it be assumed, for example, that an excessive overload occurs on the circuit controlled by the circuit breaker, including the movable contact assembly Il, the energization of the coil 20 of the electromagnet will be suicient t0 attract the armature 2i which is connected to the carriage 24 by the latch 26. The armature 2| and the carriage 24 initially move as a unitary structure, being restrained by the weight of the structure and the biasing spring 30. As soon as this unitary structure has travelled a short distance, however, the projection 26a of the latch 26 engages a projection 36a secured to the frame or bracket 36 and the latch 26 is disengaged from the armature 2|, allowing a rapid, forceful attraction of the armature 2| by the magnetic core I8, the armature 2| striking a hammer blow upon the tripping rod 38 and unlatching the circuit breaker of Figs. 1 and 2. By releasing the additional biasing means by initial movement of the armature 2|, it is then restrained only by its weight and a more effective tripping action may be obtained.

The magnitude of the overload required to move the armature 2| instantaneously to its operative position will be dependent, among other things, upon the normal air-gap between the armature and the core member I8, and upon the biasing eiect of the spring 3D. The former may be adjusted by means of the adjustable stop screw 35, while the latter can be varied by adjusting the screw 33 which moves the member 32 to vary the lever arm of the biasing spring 3U about the pivot 25.

On the other hand, if the overload upon the controlled circuit is a moderate one, it will be insutlicient to move the armature 2| to its operative position against the restraining force of the additional biasing elements. Under these conditions, however, a current will be induced in the heating coil or element 4|) which, for moderate overloads,

will be roughly proportional to the magnitude of the load current. This heater element is in intimate contact with the bimetallic strips cornprising the thermal element 39 and, after a predetermined time delay, dependent upon the thermal characteristics of the elements 39 and 40, the element 39 will be deflected by an amount suflicient to move the projection 42e of the link 42 into engagement with the latch 26 to release the latter. The overload condition will effect a suicient energization of the coil 2D to attract the armature 2| to its operative position, striking the trip rod 38 and opening the circuit breaker.

In this connection, it is to be noted that a very small unlatching force is required from the thermal element 39.k In the first place, the biasing spring of the latch 26 is connected to the lower end of the thermal element 39 so that, as it deflects to release the latch 26, the spring 2l is correspondingly released. In other words, the thermal element 39 is not loaded by the biasing spring of the latch 26 in releasing the latch.

The biasing spring 2l is effective to secure a rm engagement between the latch 26 and the extension 2| a of the armature 2| at the latching surface 2Gb, due to the wedging action of the lower surface of the latch detent, and thus renders the overload latch substantially shockproof. The magnetic attraction upon the armature 2| periodically passes through zero with the alternating flux of the core I8 so that the frictional force at the latch surface 26h due to the attraction of the armature also periodically passes through zero. It is possible. therefore, for the thermal element 39 to store energy resiliently during that portion of the cycle of alternating flux when the frictional engagement at the latch surface is greater than the unlatching force of the thermal element and to operate the latch 26 at the point of Zero ux, and thus zero frictional constant.

' l0 proportional to the energization of the coil 30 so that the time delay in the unlatchingl of the device by the thermal element 39 is roughly inversely proportional to thev magnitude of the overload; that is, the time-energization characteristic is Under. heavier overloads, however, the core member i8 is designed to partially saturate while under excessive overloads, such as short circuits, the core member I8 may be completely saturated. By way of example only, it may be f' stated that it has been found satisfactory toA design the core memberl for saturation between 175% normal rating (full load single phase current when applied to a three phase circuit) and 500% or 600% rating (corresponding to normal motor starting current) and preferably around 300% rating. As the saturation of the core member increases, the effective inductive coupling with the heating element l0 decreases with the result that the time delay in the operation of the thermal element decreases less rapidly than inversely as the magnitude of the overload, approaching a constant time Adelay as the core member i8 approaches complete saturation; that is, the time-energization constant increases in magnitude. 'I'his feature may be of advantage in connection with the starting of motors drawing a heavy saturating current.

` In addition, the time delay for any particular value of overload may be adjusted by means ol the adjusting knob and its Connected mechanism. An angular adjustment of the knob 425 rotates the threaded rod di correspondingly and moves the link l2 longitudinally of the rod 4I,

thus varying the movement required of the thermal element 39 to release the latch 23. The time delay will, of course, be' dependent directly upon the extent of the movement required of the thermal element 39. This time delay adjustment, also, is substantially uniniiuenced by vibration or shocks tothe apparatus. Since the adjustment of. the thermal element 39 is dependent upon the ambient temperature, an adjustment for such ambient temperature may be secured by loosening the screws 41 and moving the scale dial or plate 48 with respect to the other elements. The

plate 48 and the projection 48a,:ooperating with the stop 5| to limit the adjustment of the thermal element, will thus bear a different relationship to the operating rod 4l and link 42 for the same indication of the plate 48, to compensate for variations in ambient temperature.

As shown clearly in Figs. 8 and 9, the strips 39a and 39h are in intimate contact with the two sides of the heaterV coil 40 and are retainedin such relationship by the spring-biased screws 40e (Fig. 3). By forming the heater coil 40 so that is diverges from the thermal element 39 in the direction of deflection, the intimacy of contact therebetween is increased upon deflection of the thermal element. uThis intimacy of thermal contact may be increased by the modification shown in Figs. 12 and 13 in which the sides of the heater coil 40y are b-ent to extend in the direction of deflection of the thermal strips 39a and 39h. By using separate heater and thermal aovaeea by changing the heater coil to one of different resistance and thermal characteristics.

In Fig. 14a is shown a modified schematic diagram of certain elements of a circuit breaker as applied to a direct. current circuit breaker. In this case, Kthe thermal element 33 is connected directly in circuit with the circuit breaker contacts, eitherV across a shunt, or directly in se" ries, as illustrated. It will be understood that the structural arrangement of elements is similar to that of the preceding figures, and the principles of operation the same.

While I have described what I at present consider the preferred embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made Without departing from -.my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within `the true` spirit'u and scope of my invention.

What I claimis:

1. An electroresponsive device comprising an electromagnet, an armature member therefor pivoted at one end and biased to a normal position and movable' to an operative position in reelectromagnet, a pivoted armature member there-i for biased to a normal position and movable to an operative position in response'to predetermined energization of said electromagnet, a member movable co-pivotally with said armature member including a spring for additionally biasing said armature member to its normal position, a latch supported by one of said members and normally in latching engagement with the other of said members, and overload means responsive to the energization of said electromagnet for moving said latch relative to its supporting member to disengage said latch from said other member.

3. An electroresponsive device comprising an electromagnet, a pivotally mounted armature therefor biased to a normal position and movable to an operative position in response'to a predetermined energization of said electromagnet, means for additionally biasing said armature toits normal position including a pivotally mounted carriage, a latch mounted on said carriage and normally interconnecting said carriage and said armature for movement together, and time delay means responsive to the energization of said electromagnet for moving said latch relative to said carriage to release said arma-- ture.

4. An electroresponsive device comprising an electromagnet, an armature thereforbiased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means forv additionally biasing said armature to its normal position 5 including a spring, means including a disengageable member directly interconnecting said spring and said armature, time delay means responsive to the energization of said electromagnet for disengaging said member and means operable upon l a predetermined movement of said armature and said disengageable member towards said operative position to remove said additional bias from said armature.

5. An electroresponsive device comprising an l electromagnet, a pivotally mounted armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means for additionally biasing said armature to its normal position including a pivotally mounted carriage, a latch pivotally mounted at the outer end of said carriage and normally interconnecting said arrnature and said carriage for movement together, a biasing spring connected to restrain said carriage, means for adjusting said biasing spring, and time delay means responsive to the energization of said electromagnet for releasing said latch.

6. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energizetion of said electromagnet, means including a latch engaging said armature and movable therewith for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, time delay means responsive to the energization of said electromagnet for releasing said latch and means effective, upon initiation of movement of said armature in response to said increased energization of said electromagnet, independently and positively to release said latch. i

7. An electroresponsive device for an electric circuit comprising a supporting member, an operating member movable from a normal position to an operative position, means including a deflecting thermal element for controlling and imparting a time delay into the movement of said member,

means securing one end of said thermal eiement in xed position, a heating member energized upon current owthrough said circuit for heating said Athermal element, and resilient means for biasing said heating member into intimate heat exchanging relation with said thermal element.

8. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a disengageable member normally engaging said armature and movable therewith for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a thermal element effectivelto disengage said member, and a heater for saidi thermal element comprising a closed conductive-,loop surrounding the core of said electromagnet.

9. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a disengageable member normally engaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operativ-e position, a defiecting thermal element effective to disengage said member, and a heater for said thermal element comprising a closed conductive loop surrounding the core of said electromagnet and in intimate Contact with said thermal element, said heater being shaped to conform approximately to the shape of said thermal element when deflected, whereby the intimacy of contact therebetween is increased upon deection of said thermal element.

l0. In an electroresponsive device, a thermal control mechanism comprising a bimetallic thermal element, a heating coil formed by a closed conductive loop for heating said element, means securing one end of said element in intimate contact with a part of said coil, a portion of said element being movable and another part of said coil extending in the direction of movement of said movable portion of said element when heated thereby to maintain said coil and element in close heat exchanging relation during said movement of said movable portion of said element.

11. In an electroresponsive device, a thermal control mechanism comprising a substantially rectangular heating coil, a pair of bimetallic strips disposed in intimate contact with two arms of said rectangular coil and secured at one end, and an operating member interconnecting said strips at their free ends.

12. In an electroresponsive device, a thermal control mechanism comprising a substantially straight armed heating coil, and a bimetallic strip disposed in intimate contact with the straight arm of said coil, said coil being shaped to conform approximately to the shape of said bimetallic strip when deflected, whereby the intimacy of contact therebetween is increased upon deiiection of said strip.

13. In an electroresponsive device, a thermal control mechanism comprising a substantially rectangular heating coil, a pair of bimetallic strips disposed in intimate contact with two arms of said rectangular coil and secured at one end, said coil being shaped to diverger from the free ends of said strips when undeflected in such a direction that the intimacy of contact therebetween is increased upon deflection of said strips, and an operating member interconnecting said strips at their free end. A

14. In an electroresponsive device including an electromagnet, a thermal control mechanism comprising a substantially rectangular closed conductive loop surrounding the core of said electromagnet, a pair of bimetallic strips disposed in intimate contact with two arms of said loop and secured at one end, and an operating member interconnecting said strips at their free ends.

l5. In an electroresponsive device including an electromagnet having a core section saturable within the range of operation of the device, a thermal control mechanism comprising a flat bimetallic thermal element, a single closed conductive loop surrounding said saturable core section, a portion of said single loop extending parallel to said thermal element and disposed in intimate heat exchanging relation therewith.

16. In an electroresponsive device including an electromagnet having a core section saturable within the range of operation of the device, a

thermal control mechanism comprising a substantially rectangular closed conductive loop surrounding the saturable core section, and a pair of bimetallic strips disposed in intimate contact with tvvo arms of said loop and secured at one end, and an operating member interconnecting said strips at their free ends.

17. In an electroresponsive device, a thermally controlled latching mechanism comprising 10 a latch member operable from a latching position to a releasing position, a deiiecting thermal element for operating said latch member to said releasing position and a spring for biasing said latch to said latching position and for simultaneously biasing said thermal element for deflection in the direction to release said latching member, said spring after movement of said latching member to said releasing position being operative to bias said latching member to said latching position.

18. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latch engaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a deecting thermal element heated in accordance with the energization of said electromagnet, an operating member one end of which is operatively associated with said thermal element and the opposite end of which is operatively associate-d with said latch, said thermal element upon a predetermined deflection thereof moving said member, to release said latch, and a spring interconnecting said latch and said element for biasing said latch into said engagement and toward the correspending end of said member and for biasing said element and said member toward said latch so that upon deection of said thermal element the bias on said latch is not increased.

19. An electroresponsive device comprising an electromagnet, an armature therefor biased to,J

a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latch engaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a deecting thermal element heated in accordance with the energization of said electromagnet, a spring interconnecting and biasing together said .n thermal element and said latch independently of the position of said armature, and an operating `member connected to said thermal element and eifective, upon a predetermined deflection thereof, to release said latch.

20. An electroresponsive device comprising an electromagnet, an armature therefor biased t0 anormal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latch engaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a deilecting thermal element heated in accordance with the energization of said electromagnet, an operating member connected to said thermal element, and a link adjustably connected to said operating member and movable therewith to release said latch.

2l. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization able therewith to release said latch.

22. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latch engaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a delecting thermal element heated in accordance with the energization of said electromagnet, a threaded rod connected to said thermal element and movable in response to deflection thereof, an operating link engaging said threaded rod and restrained from rotation about said rod, said link being effective to release said latch upon movement by said thermal element, and means for adjusting the angular position of said rod to calibrate the device.

23. An electroresponsive device comprising a supporting frame including an electromagnet as a unitary part thereof, an armature for said electromagnet biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latchengaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a defiecting thermal element heated in accordance with the energization of said electromagnet, a threaded' rod connected to said thermal elementl and movable in response to deflection thereof, an operating link engaging said threaded rod and engaging. a slot in said frame to prevent rotation thereof about said rod, said link being movable upon deflection of said thermal element to release said latch, and an adjusting member pivotally mounted on said frame and slidably engaging said rod, whereby adjustment of said member adjusts said rod, but said rod is freely movable longitudinally with respect to said knob.

24. An electroresponsive device comprising an velectromagnet, an armature structure therefor electromagnet for releasing said latch.

25. An electroresponsive device comprising an electromagnet, an armature therefor biased to acrobat a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latch provided with a stop surface engaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, resilient means independent of said biasing means for securing a iirm engagement between said armature and said stop surface of said latch, and means responsive to the energization of said electromagnet for releasing said latch, said last-named means having a time delay in its operation de creasing substantially inversely with the energization of said electromagnet Afor magnitudes of energization below a predetermined value, said electromagnet including means for modiiyingV said time delay whereby it decreases at a less rapid rate for magnitudes of energization above said predetermined value.

26. An electroresponsive 'device for an electric circuit comprising a member biased to a normal position and movable to an operative position, operating means responsive to the energization of said circuit for biasing said member to said operative position, the magnitude of said bias being proportional to the magnitude oi the current iiowing in the circuit, means including a latch engaging said member and movable therewith for additionally biasing said member to its normal position to'increase the energization of said operating means required to move it to its operative position, time delay means responsive to the energization of said circuit for releasing said latch, and separate tripping means engaged by said latch after a predetermined movement of said member and said latch toward said operative position for positively releasing said latch thereby to remove said additional bias whereupon said operating means is eiicective to move quickly said member.y to said operative position.

27. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latch engaging said armature for additionally biasing said' armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a thermal element heated in accordance with the energization of said electromagnet, a connection between said thermal element and said latch for releasing the latter, means for adjusting said connection, an indicating scale associated with said adjusting means, and means for adjusting said scale to correct for variations in ambien temperature.

28. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, means including a latch engaging said armature for additionally biasing said armature to its normal position to increase the energization of said electromagnet required to move it to its operative position, a deecting thermal element heated in accordance with the energization of said electromagnet, a threaded rod connected to said thermal element, an operating link engaging said rod and eiective torelease said latch upon deflection of said thermal element, means for restraining said link from rotation about said rod, a pivotally mounted adjusting member slidably engaging said rod for angularlyrotating the same, an indicating scale associated with said adjusting member, and means for adjustingsaid scale to correct for variations in the ambient temperature.

29. An electroresponsive device comprising an electromagnet, an armature therefor, a disengageable member normally restraining said armature in an inoperative position, and a thermal control mechanism tor releasing said member including a thermal element, a manually operable adjusting member for said thermal element rotatable :for a single revolution for adjusting the temperature at which said disengageable member is released, a position indicating dial cooperating with said adjustable member, and a spring lock for said adjustable member.

30. An electroresponsive device comprising an electromagnet, an armature therefor biased to a normal position and movable to an operative position in response to a predetermined energization of said electromagnet, a deiiecting thermal element eective to impart a time delayinto the movement or" said armature to operative position, means securing one end or" said element in a fixed position, a member heated in accordance with the energization of said electromagnet, and resilient means for biasing said member into intimate heat exchanging relation with said thermal element.

3l. An overload trip unit for a circuit interrupter comprising an electromagnet responsive to the energization of the circuit interrupter, an armature movable by said electromagnet through a given air-gap to trip said interrupter, a latch for restraining said armature against movement, means operable with a time delay for releasing said latch during normal overload conditions of the circuit, and separate means operable without a time delay for releasing said latch upon the occurrence of abnormal overload conditions of said circuit.

32. An electroresponsive trip unit for a switch connected in a circuit subject to changes in an electrical condition comprising an electromagnet energized from said circuit and provided with an armature movable to trip said switch, a latch for restraining said armature against movement, means responsive to said condition and operable with a time delay with changes in said condition below a predetermined value for releasing said latch, and separate means responsive to said condition and operable without a time delay with changes in said condition above a predetermined value for releasing said latch.

HERBERT C. GRAVES, JR.

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