US3302142A

US3302142A - Load responsive switch apparatus

Info

Publication number: US3302142A
Application number: US357009A
Authority: US
Inventors: Piechotta Josef Max
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-03-26
Filing date: 1964-03-26
Publication date: 1967-01-31
Anticipated expiration: 1984-01-31

Description

Jan; 31, 1967 J, PlECHOTTA I 3,302,142

LOAD RESPONSIVE SWITCH APPARATUS Filed March 26, 1964 2 Sheets-Sheet 1 43 11c. 29 POWER Q SOURCE 40 i I I I 9* i i 0 t l 331' 25 v I I I 26 I l I l 30 D 42 If n T 4/ 44 7 I I l 46 INVENTOR.

1 J09? MAX PIECHOTTA 2/ 0 BY ndrus Star 2 20 7 i K ATfomvEYs Jam 1967 J. M- PIECHOTTA LOAD RESPONSIVE SWITCH APPARATUS Filed March 26, 1964 2 Sheets-Sheet 2 I'NVENTOR.

JOSEF MAX PIECHOTTA BY find/"us Star/g2 United States Patent 3,302,142 LOAD RESlPONSIVE SWITCH APPARATUS Josef Max Piechotta, 2138 S. 18th St., Milwaukee, Wis. 53205 Filed Mar. 26, 1964, Ser. No. 357,009 2 Claims. (Cl. 335128) This invention relates to an electrical load responsive switch apparatus and particularly to such a switch apparatus for operating an indicator or recording means in accordance with the operating timeof an arc welding unit or the like. This application is a continuation-in-part of applicants copending application entitled Load Responsive Switch Apparatus filed December 10, 1962 with Serial No. 243,565.

In arc welding and arc cutting shops, a record of the actual welding time during a given base period may be maintained for various reasons. The record may be employed for supervisory purposes, efficiency studies, calculation of wages or for any other purpose desired. Many different indicating systems have been heretofore suggested. For example, US Patent 2,340,114 discloses an indicator for use in a welding circuit for recording the operating time therein. In accordance with that patent, a generally conventional relay is employed to open and close the circuit.

Indicators for shop practice must of necessity be rugged, reliable units which can withstand the atmospheric conditions as well as the conventional shop handling and use inherently encountered in the shop. Further, in large shops Where a relatively great number of small individual machines are in use, the recording and pickup structure should be of a relatively simple and eflicient design to minimize cost of installation, maintenance and servicing.

The present invention is particularly directed to a very rugged and reliable switch structure of a relatively simple and inexpensive construction and installation.

In accordance with the present invention, a magnetic member generally defining a channel-shaped passageway is provided with a movable portion overlying or spanning the opening to the channel-shaped member. The movable portion is resiliently coupled to directly actuate a suitable switch. A portion of the main load conductor, preferably in the form of a separate metal strip, is passed through the channel-shaped portion. When the welding process is initiated, the load current flowing through the conductor establishes a magnetic field which is concentrated within the U-shaped magnetic frame and the movable portion spanning the opening thereof. At a preselected current level, the movable portion is attracted to complete the magnetic path in accordance with known phenomenon and thereby moves the switch to a closed or recording position. The resilient mounting of the switch unit allows variations of the pull-in current and thus allows adjustment of the switch unit to record only welding operations of a predetermined load characteristic.

The present invention may be constructed to respond to either an alternating or a direct current load current. In either event, the structure preferably includes a core having a U-shaped laminated core portion formed by a plurality of correspondingly figured lamination plates riveted or otherwise suitably interconnected. A relatively thin, plate-like bridge member is pivotally secured to the one arm of the U-shaped core and bridges the gap between the arms with the free end of the bridge member aligned with and overlying the end of the opposite arm of the U-shaped core portion. The laminated structure is employed to permit adjustment of the switching apparatus to preselected current ranges as well as to provide better response and action to the current levels. Within each current range, the precise triggering or actuating current isdetermined by a spring tension setting of the bridge 3,302,142 Patented Jan. 31, 1967 member as well as adjustment of the air gap between the bridge member and the core.

In providing a direct current responsive unit, the bridge member is provided with small non-magnetic spacing means secured to the inner face of the free end to positively prevent complete interengagement with the opposing face of the U-shaped core and closing of the air gap. This provides a very rapid response and breaking of the circuit by movement of the bridge plate in response to a decrease in holding current.

In an alternating current circuit, it has been found that a shorted turn should be wound about a portion of the U-shaped core immediately adjacent the free end of the bridge plate and the adjacent end of the U-shaped core. This provides very silent and reliable operation.

Applicant has found that in all cases, the AC. and DO relays can be formed with a basic similar construction with the current ranges controlled by the number of laminations employed in the U-shaped core. In A.C. circuits, looping of the load current conductor to form a winding of one, two or more turns also provides response to different current levels. In relatively high current ranges, however, the load conductor may pass directly through the U-shaped core structure and provide highly reliable operations.

The present invention thus provides a rugged and reliable current responsive switch which is of an economical construction and requires a minimum of installation, maintenance and servicing cost.

The drawings furnished herewith illustrate the best mode presently contemplated for carrying out the invention.

In the drawings:

FIG. 1 is a schematic circuit diagram incorporating a switch constructed in accordance with the present invention;

FIG. 2 is an enlarged front elevational view of a switch assembly shown in FIG.1;

FIG. 3 is a side elevational view of FIG. 2;

FIG. 4 is a view similar to FIG. 3 showing an alternative construction of a direct current responsive relay for incorporation in any suitable direct current power circuit;

FIG. 5 is a fragmentary view of FIG. 4 showing a portion of the relay similar to the illustration in FIG. 2 to clearly illustrate the present construction;

FIG. 6 is a top plan view similar to FIGS. 2 and 5 illustrating an alternative construction particularly useful and adapted to alternating current responsive circuits; and

FIG. 7 is a view similar to FIG. 4 of an alternating current relay shown in FIG. 6 and construction in accordance with the present invention.

Referring to the drawings and particularly to FIG. 1, a welding circuit is schematically shown including an electrode 1 held in spaced relation to a workpiece 2. A power source 3, shown in block diagram as a suitable D.C. (direct current) source connected by leads 4 to the electrode 1 and the work 2. A starting switch 5 is inserted in one of the leads 4 and when closed establishes a suitable voltage and power across the electrode 1 and work 2 to establish and maintain an are 6 therebetween. A switch assembly '7 constructed in accordance with the present invention is shown mounted within the power source 3 and is connected in circuit to control operation of a timer or suitable recording device 8. As more fully described hereinafter, the switch assembly 7 normally maintains the timer 8 deenergized. When switch 5 is closed to establish and maintain are 6, the current flow in the leads 4 actuates the switch assembly 7 to complete the circuit to the timer 8 and thereby make an accurate record of the welding or load time.

Referring to FIGS. 13, the illustrated switch assembly 7 includes an insulating mounting base 9 with a mounting arm or wall 10 projecting perpendicularly therefrom. In the illustrated embodiment of the invention, the wall 18 is shown as a separate member interconnected to the base 9 by suitable bolts 11. The base 9 and wall 10 may, if desired, be integrally formed. The base 9 is secured in any suitable manner within the power source 3 with the wall 10 projecting horizontally therefrom.

A generally U-shaped frame 12 formed of magnetic material has one arm secured to the wall 13 as by suitable screws 13 which pass through the wall and thread into suitably tapped openings in a side arm of the U-shaped frame 12. The frame 12 is mounted with the common web or base of the member disposed in slightly spaced relation to the base 9 as at 14 in FIG. 3. A bridging plate 15 of megnatic material spans the open end of the frame 12 with the one end of the plate 15 aligned with the inner arm 16 of frame 12 and the opposite end projected outwardly beyond the outer arm 17 of frame 12. The plate 15 adjacent the outer arm is provided with suitable edge notches 18 aligned and mating with upstanding or outwardly projecting ears 19 integrally formed on the opposite edges of the outer arm of member 12. A small U-shaped bracket 20 is bolted as by bolts 21 or otherwise secured to the exterior of the outer arm 17 with an extension of the plate 15 disposed generally centrally thereof. A coil spring 22 is disposed between the extension of plate 15 and the inner surface of the outer arm of bracket 20 and continuously urges the plate 15 to pivot on the outer edge of the arm 17. Suitable locating

bosses

23 and 24 are shown respectively on the extension of plate 15 and the arm portion of the bracket 20 to align and hold the spring 22 in place.

An L-shaped stop arm 25 is secured to the outer wall 11) by the screws 13 for frame 12 and projects inwardly over the upper edge of wall 10 and the outer or free end of the plate 15. A stop screw 26 threads through a suitable opening in the arm 25 and serves as a stop for the plate 15 for limiting the outward pivotal movement thereof under the action of coil spring 22. A lock or positioning nut 27 is threaded onto the stop screw 26 and serves as an adjustable positioning or locating member for screw 26. The frame 12 and plate 15 form a generally rectangular magnetizable member or unit having the one movable side pivotally mounted or attached to an adjacent side and with an air gap formed between the opposite and free end of the movable side and the adjacent side of the unit.

A conducting strap 28 is formed of a strip of copper or the like and is connected in series and forms a main current carrying portion of one of the leads 4. The strap 28 projects through the passageway defined by frame 12 and is secured to the base 9 by

suitable attachment bolts

29 and 30 which pass downwardly through suitable openings in the strap on opposite sides of the frame 11 and thread into suitably tapped openings in the base 9. Suitable insulating spacers 31 encircle the

respective bolts

29 and 30 between the strap 28 and the base 9 to properly locate the strap with respect to frame 12. As most clearly shown in FIG. 3, the strap 28 is located adjacent to but slightly spaced from the web portion of the U- shaped magnetic frame 12. A centrally located disc 32 is shown fixed to the base of frame 12 in alignment with strap 28.

Generally, the coil spring 22 holds the plate 15 with the free end spaced from the arm 16 of the frame 12. However, when the arc 6 is struck the current through the strap 28 establishes a magnetic field which is concentrated in the frame 12 and the plate 15. As a result, the free end of plate 15 is pulled into engagement with the arm 16 and completes the magnetic path therethrough. The movement of arm 16 actuates the switch assembly 7 and results in energization of timer 8, as follows.

L-shaped

contacts

33 and 34 are secured to the opposite edges of the wall 10 with suitable bent over portions projecting slightly inwardly. Leads 35 and 36 are connected respectively to the

contacts

33 and 34 and in series with the timer 8 to a suitable source of power for operating timer 8. A contact plate 37 is secured to the plate 15 as hereinafter described. Contact plate 37 includes a bifurcated end defining

contact carrying arms

38 and 39 extending to either side of the wall 10 and terminating in alignment with the bent over portions of the

contacts

33 and 34. When the contact plate 37 engages

contacts

33 and 34, the current path therebetween is completed and operates the timer 8.

The contact plate 37 is secured to the plate 15 in the following manner in the illustrated embodiment of the invention.

An insulating spacer 40 is mounted between

plates

15 and 37 and includes a tubular boss 41 projecting through an opening in the central portion of plate 37. A stud bolt 42 passes through the boss 41 and a clamping nut 43 is threaded thereon to clamp the spacer 40 to the plate 15. A small coil spring 44 encircles the boss 41 and is compressed between the nut 43 and the contact plate 37 to resiliently hold the contact plate 37 in position with the

contact arms

38 and 39 in alignment with the

contacts

33 and 34.

A small lip 45 is provided integrally formed on the back edge of the contact plate 37 and mates with a recess or opening 46 in the adjacent portion of the spacer 49 to guide and hold the contact plate in position.

In summary, the illustrated embodiment of the invention operates as follows. The start switch 5 is closed to establish and maintain the are 6 between the electrode 7 1 and the work 2. The load current passes through the conducting strap 28 and establishes a corresponding magnetic field in the magnetic frame 12. The magnetic forces attract the plate 15 and cause it to pivot, counterclockwise as viewed in FIG. 3, against the force of the coil spring 22 to close the gap between the free end ofthe plate 15 and the corresponding arm 16 of the frame 12. This pivotal movement of the plate 15 similarly carries the contact plate 37 until the

contact arms

38 and 39 engage

contacts

33 and 34. The final movement of plate 15 further compresses the coil spring 44 and resiliently holds the

arms

38 and 39 in engagement with the

contacts

33 and 34. As a result, a conductive path is established between

contacts

33 and 34 and the timer 8 is energized to record the welding operation.

When the are 6 is broken and the current through the strap 28 drops to zero, the magnetic field in frame 12 disappears and coil spring 22 pivots the plate 15 in a clockwise direction as viewed in FIG. 3. As a result, the contact plate 37 moves outwardly and breaks the circuit between the

contacts

33 and 34 to again deeriergize the timer 8.

The switch assembly of the present invention may also distinguish between certain welding processes and only record those employing a predetermined minimum welding current. For example, the stop screw 26 determines the spacing of the free end of the plate 15 from the adjacent arm 16 of the frame 12. As the spacing is increased a greater current is required to establish a magnetic field of suflicient strength to attract the plate 15 sufficiently to bridge

contacts

33 and 34. The tension of the coil spring 22, which opposes the pivoting of plate 15 by the magnetic field, can also be selected or set to restrict closure of the switch unit until a minimum welding current passes through strap 28.

Although not shown, other electroresponsive devices may be employed with or in place of timer 8. An indicating lamp maybe connected to indicate when welding is being done. Or, a counter may be inserted in the circuit to record the separate welding operations made.

device for recording or otherwise detecting changes in arc welding or other similar current circuits, applicant has found that the relay structure shown in FIGS. 4 and 5 provides an even more reliable and versatile relay unit for direct current circuits.

The relay of FIGS. 4 and 5 substantially corresponds to that illustrated in FIGS. 1-3 and the corresponding elements in the two embodiments are generally similarly numbered with the following description given to clearly illustrate and describe the modifications and improvements.

Referring particularly to FIG. 4, the embodiment of FIGS. 4 and 5 includes a U-shaped core 12 of a crosssection generally similar to that shown in FIG. 3. However, the core or frame 12 of FIGS. 4 and 5 is built up of a plurality of individual U-shaped laminations 47 disposed in stacked or nested relation and interconnected by a plurality of rivets 48. In the illustrated embodiment of the invention, a pair of rivets 48 is secured to the outer ends of each

arm

16 and 17 of the U-shaped frame 12 and four rivets 48 are distributed in a symmetrical relation in the base portion. A bridging plate is shown including a pair of laminations 49 interconnected by a plurality of rivets 50. The core plate 15 is pivotally mounted adjacent the arm 17 of frame 12 by an improved mounting means including a mounting shaft or rod 51 which extends through a passageway formed by a raised portion 52 in the outer lamination 49 of bridging plate or member 15. A hearing plate 53 is secured to the outer face of the arm 17 by a pair of screws 54 or the like. The plate 53 includes a pair of upstanding ears or flanges 55 which project outwardly to either side of member 15 and are provided with properly located apertures to receive the mounting rod 51; Lock pins 56 shown as conventional cotter keys are passed through appropriate openings in the ends of rod 51 to hold it in place. As in FIGS. 1 through 3, a load conductor 57 is mounted extending through the generally rectangular core unit formed by the U-shaped frame 12 and the bridging plate or member 15.

In accordance with the embodiment of the invention illustrated in FIGS. 4 and 5, the free end of the laminated member 15 is aligned with the end face of arm 16. However, in the embodiment of the invention shown in FIGS. 4 and 5, rivets 58 are secured to the member 15 and project outwardly from the innermost face thereof in alignment with the arm 16. The rivets 58 are formed of a suitable nonmagnetic material such as brass. When the conductor 57 is energized and the member 15 is attracted to engage arm 16 of core frame 12, a selected air gap is maintained therebetween.

The contact plate 37 is mounted to the bridging member 15 for selective interengagement of the contacts at the ends of

contact arms

38 and 39 with

contacts

33 and 34, as in FIGS. 1 through 3, inclusive.

Generally, the operation of the embodiment of the invention illustrated in FIGS. 4 and 5 will correspond to that shown in FIGS. 1-3. Load current in the conductor 57 creates a magnetic flux within the generally rectangular core formed by

laminated members

12 and 15 which attract the bridging member 15. At a selected level, the magnetic force overcomes that of the coil spring 22 and closes the air gap. As a result, the contacts engage and provide a conductive path between

contacts

33 and 34. When the current drops to zero or some other selected level, the magnetic field disappears or decreases sutficiently to allow the coil spring 22 to pivot bridging member 15 and open the contacts. The nonmagnetic rivets 58 or other similar spacing means which might be used assure a positive and rapid opening of the circuit to insure reliable and long-life operation of the system. The laminated core 17 including the stacked lamination 47 provides a very simple and convenient means for adjusting the current range of the relay unit. Thus, by reducing the number of laminations in the core, it will provide direct relationship with the current ranges being operated upon.

The previous embodiment-s are shown applied to a direct current circuit. A preferred construction for an alternating current relay unit in accodance with this invention is shown in FIGS. 6 and 7.

In FIGS. 6 and 7, a pair of alternating current relays 59 and 60, constructed in accordance with the present invention, is shown carried by a suitable mounting board 61 or the like. The relays 59 and 60 are similarly constructed and the relay 59 will be specifically described and corresponding elements of relays 60 identified by similar primed numbers. The relay structures of FIGS. 6 and 7 also substantially correspond to that of the previous embodiments and the elements corresponding to those of FIGS. 1-3 are similarly numbered and only the modifications are described.

Referring particularly to FIGS. 6 and 7, the AC. relay 59 includes the U-shaped frame 12 formed with a plurality of laminations 62 generally in accordance with the illustration and teaching shown in FIGS. 4 and 5. Similarly, the bridging plate or member 15 is formed of a pair of laminations 63 and is pivotally mounted adjacent the one end of the U-shaped core 12 by an adjustable pivotal mounting assembly 64 corresponding to that shown in FIGS. 4 and 5.

A contact unit 65 is also similarly mounted on the opposite or free end of the bridging member 15, as shown in FIG. 1.

In the illustrated embodiment of the invention shown in FIGS. 6 and 7, however, the switch mounting wall 10 to which the one arm 16 of the core frame 12 is secured as in FIGS. 15 is extended below the base of frame 12 to provide a suitable enlarged Winding space 66 between the base of the frame 12 and the mounting board 61. One or more insulation wraps 67 are wound upon the base and an alternating current winding 68 is wound on the base. As most clearly shown in FIG. 6, relay 59 is provided with a single turn winding 68 Whereas the corresponding winding 68' of relay 60 includes two turns.

If the relay is employed with substantial line currents, a straight through winding such as shown in the direct current relay of FIGS. 1-3 may be used. The number of turns provides a convenient and simple means of controlling the current range for which the device is operable. Further, the number of turns is minimal in most practical ranges and consequently the power consumed by the relay is inconsequential.

In FIGS. 6 and 7, a small slot or groove 69 is formed in the outermost end of the arm 16 and the mounting wall 10 is recessed immediately adjacent the outer end of the arm 16, as at 70. A conducting brass strap or ring 71 has one end disposed within the groove 69 and encircles one-half of the arm 16. The ring 71 forms a short circuited single turn which provides highly reliable and silent operation of the alternating current relay. Further, as most clearly shown in FIG. 6, the spacing rivets of FIGS. 4 and 5 have been eliminated. However, member 15 may include the rivet holes to provide versatility of assembling such that the same member 15 may be employed for both the direct current and the alternating current relays. Similarly, the modification to the mounting plate and the outer end of the arm 16 can be made without any change in the basic structure of the assembly.

Generally, the alternating current relay operates in substantially the same manner as the direct current relay with the relay pulling in accordance with the adjustment or setting of the spring 22 and the stop screw 26. Additionally, the precise current level at which the relays are actuated will be controlled by the number of turns in the windings. In operation, it has been found that the relays of FIGS. 6 and 7 are closed and opened with a rapid, snap action. Further, once the relay has been energized or closed, it is held closed without any vibration of the plate member 15 as a result of the short circuited conductor 71 on the core arm 16 of member 12.

The present invention provides a very rugged and reliable structure particularly adapted for shop practice such as welding and similar processing shops.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. A load detecting apparatus adapted to respond to the current in a load circuit, comprising a generally rectangular magnetizable member having a main laminated U-shaped frame and a movable side pivotally mounted at one end to an adjacent arm of the frame, said main laminated U-shaped frame including a greater plurality of laminations than said movable side,

a spring guide secured to the arm of the frame and defining a wall parallel to the movable side,

a resilient means disposed between the movable side and the wall and urging said movable side to pivot outwardly and establish an air gap between the free end thereof and the aligned arm of the member,

adjustable stop means adjacent the free end to preset the length of the air gap between the movable side,

a conductor passing through said magnetizable member and adapted to be connected in series in the load circuit, current in said conductor establishing a magnetic field in said magnetizable mem-ber attracting said movable side,

a pair of spaced contacts mounted adjacent the free end of the movable side,

a contact plate having contact arms aligned with the spaced contacts and superimposed over the movable side of the magnetizable member,

an insulating spacer disposed between the contact plate and the movable side and having a tubular projection extending through an opening in the contact plate,

bolt means passing through the tubular projection and clamping said spacer to the movable side of the magnetizable member,

a coil spring encircling said projection and compressed between the contact plate and the outer end of the bolt means, and

means to prevent relative rotational movement of the spacer and the contact plate on said bolt means.

2. The relay apparatus of claim 1 having nonmagnetic rivets secured within openings in the free end of the movable side in alignment with the adjacent arm of the frame and extending from the inner face to establish a selected minimum spacing between the free end of the movable side and the adjacent arm.

References Cited by the Examiner UNITED STATES PATENTS 1,108,320 8/1914 Berdon 307- X 1,503,980 8/1924 Carichoff 317-198 1,852,614 4/ 1932 Johnson et al.

1,934,264 11/1933 Hefner 340-253 2,157,844 5/1939 Armstrong et a1. 317-184 2,159,837 5/1939 Bab-b et al 317-184 X 2,341,896 2/ 1944 Bellows et al. 200-87 2,517,052 8/1950 Swinehart 200-87 2,528,744 11/1950 Fehr 340-253 2,584,901 2/1952 Miller et al. 317-184 X 2,619,569 11/1952 Savage 200-87 2,749,485 6/1956 Ober et a1 317-198 X 2,918,547 12/1959 Titus 317-198 X 3,177,480 4/1965 Sankey 340-253 FOREIGN PATENTS 1,164,591 10/1958 France.

NEIL C. READ, Primary Examiner.

D. K. MYER, Assistant Examiner.

Claims

1. A LOAD DETECTING APPARATUS ADAPTED TO RESPOND TO THE CURRENT IN A LOAD CIRCUIT, COMPRISING A GENERALLY RECTANGULAR MAGNETIZABLE MEMBER HAVING A MAIN LAMINATED U-SHAPED FRAME AND A MOVABLE SIDE PIVOTALLY MOUNTED AT ONE END TO AN ADJACENT ARM OF THE FRAME, SAID MAIN LAMINATED U-SHAPED FRAME INCLUDING A GREATER PLURALITY OF LAMINATIONS THAN SAID MOVABLE SIDE, A SPRING GUIDE SECURED TO THE ARM OF THE FRAME AND DEFINING A WALL PARALLEL TO THE MOVABLE SIDE, A RESILIENT MEANS DISPOSED BETWEEN THE MOVABLE SIDE AND THE WALL AND URGING SAID MOVABLE SIDE TO PIVOT OUTWARDLY AND ESTABLISH AN AIR GAP BETWEEN THE FREE END THEREOF AND THE ALIGNED ARM OF THE MEMBER, ADJUSTABLE STOP MEANS ADJACENT THE FREE END TO PRESET THE LENGTH OF THE AIR GAP BETWEEN THE MOVABLE SIDE, A CONDUCTOR PASSING THROUGH SAID MAGNETIZABLE MEMBER AND ADAPTED TO BE CONNECTED IN SERIES IN THE LOAD CIRCUIT, CURRENT IN SAID CONDUCTOR ESTABLISHING A MAGNETIC FIELD IN SAID MAGNETIZABLE MEMBER ATTRACTING SAID MOVABLE SIDE, A PAIR OF SPACED CONTACTS MOUNTED ADJACENT THE FREE END OF THE MOVABLE SIDE, A CONTACT PLATE HAVING CONTACT ARMS ALIGNED WITH THE SPACED CONTACTS AND SUPERIMPOSED OVER THE MOVABLE SIDE OF THE MAGNETIZABLE MEMBER, AN INSULATING SPACER DISPOSED BETWEEN THE CONTACT PLATE AND THE MOVABLE SIDE AND HAVING A TUBULAR PROJECTION EXTENDING THROUGH AN OPENING IN THE CONTACT PLATE, BOLT MEANS PASSING THROUGH THE TUBULAR PROJECTION AND CLAMPING SAID SPACER TO THE MOVABLE SIDE OF THE MAGNETIZABLE MEMBER, A COIL SPRING ENCIRCLING SAID PROJECTION AND COMPRESSED BETWEEN THE CONTACT PLATE AND THE OUTER END OF THE BOLT MEANS, AND MEANS TO PREVENT RELATIVE ROTATIONAL MOVEMENT OF THE SPACER AND THE CONTACT PLATE ON SAID BOLT MEANS.