US3317869A

US3317869A - Reed switch having large current carrying capacity

Info

Publication number: US3317869A
Application number: US469507A
Authority: US
Inventors: Richard A Funke
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1965-07-06
Filing date: 1965-07-06
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02

Description

R. A. FUNKE May 2, 1967 REED SWITCH HAVING LARGE CURRENT CARRYING CAPACITY 2 Sheets-Sheet 1 Filed July 6, 1965 IN V EN TOR. RICHARD A. FUNKE R A. FUNKE 3,317,869 REED SWITCH HAVING LARGE CURRENT CARRYING CAPACITY May 2, 1967 2 Sheets-$heet 2 Filed July 6, 1965 Patented May 2, 1967 3,317,869 REED SWITCH HAVING LARGE CURRENT CARRYING CAPACITY Richard A. Funke, Milwaukee, Wis, assignor to Allen- Bratlley Company, Milwaukee, Wis, a corporation of Wisconsin Filed July 6, 1965, Ser. No. 469,507 Claims. (Cl. 335-154) This invention pertains to an electrical switch which is responsive in relay fashion to an externally applied magnetic field.

While not so limited, the switch of this invention can be included within the reed switch classification. Reed switches are generally of a small construction and essentially consist of magnetic reed members which have terminals at their free ends and overlap at their other ends to perform the dual function of magnetic gap and electrical contacts. These magnetic members are usually enclosed by a non-magnetic material. By applying a sufiicient external magnetic field at the region of the gap, the magnetic members are attracted so as to close the switch. The well-known status of this switch in the art obviates the need for further discussion.

The switch of the invention is related to the above-described reed switch classification in that a similar small Switch construction accommodates an external magnetic field to close magnetic members; but in the invention, the magnetic gap and the electrical contacts are separated. As in the reed switch, the switch of the invention is preferably enclosed. Further significance resides in the fact that the switch of the inventon has overcome the current capacity limitations of the above-described reed switch by means of switch structure which will be described hereafter. The capacity limitation of the switch is primarily a function of size with switches comparable in size to the above-mentioned reed switch handling at least three (3) amps break, five (5) amps carry and thirty amps make at 120 volts All.

An object of this invention is to provide a magnetically responsive electric switch which is capable of closing on or making at a maximum current with respect to switch size.

A further object of this invention is to provide a magnetically responsive switch with a maximum contact force for switch size; which contact force is constant essentially throughout the break or opening of the electrical contacts.

A further object of this invention is to provide a magnetically responsive switch which incorporates a snap action during the make and break of the electrical contacts.

A further object of this invention is to provide a magnetically responsive switch which includes a wiping action between the electrical contacts during the make and break periods.

A still further object of this invention is to provide a magnetically responsive switch in which shims are used in combination with a spring so as to insure desired switch performance.

A still further object of this invention is to provide a hermetically sealed switch which is responsive to an external magnetic field and is capable of closing on or making at a maximum current for its size.

A still further object of this invention is to provide a magnetically responsive, hermetically sealed switch in which the magnetic gap is separated from the gap formed by the contacts to thereby overcome current capacity limitations which are a part of a switch combining said gaps such as found in reed switches.

A still further object of this invention is to provide a sealed switch utilizing a selected atmosphere in order to prevent sticking between the contacting members of a magnetic gap within the switch.

These and other objects of this invention will become apparent from the following description of a preferred switch embodiment. It must be noted that this embodiment is used only for purposes of explanation with the scope of the invention set forth in the appended claims.

FIGURE 1 is a cross-sectional, side View of the switch in its normally-open position.

FIGURE 2 is a cross-sectional, side view of the switch in FIGURE 1 showing the first step of switch closing, viz the electrical contacts are closed while the magnetic gap remains partially open.

FIGURE 3 is a cross-sectional, side view of the FIG- URE 1 switch showing the closed position, viz both the electrical contacts and the magnetic gap are closed.

FIGURE 4 shows a modification of the FIGURE 1 switch in which normally closed contacts have been added adjacent to the magnetic gap to thereby provide a form C switch.

Since the construction of the switches shown in FIG- URES 1-3 is the same and since the construction of the switch in FIGURE 4 is similar to thatrswitch shown in FIGURES 1-3, the following description of the elements making up the switch of the invention will be applicable to each of the figures and corresponding reference numerals will be used in each figure.

The elements of this switch are enclosed by tube 1 which is made from a non-magnetic material such as glass, which tube 1 forms seals at either end, thereof, about leads 2 and 3-.

Pole piece 8 is secured to the internal end of lead 2 and is made of a magnetic material such as No. 45 Permalloy. Pole piece 8 thus becomes the element which mechanically connects the armature assembly 9 to the lead 2. Included in armature assembly 9 is a resilient or spring member 10 which acts in cantilever fashion to support and bias the armature piece 11. In order to control the spring force of spring member 10, inner shim 12 is located between pole piece 8 and spring member 10 while outer shim 13 is correspondingly located on the opposite side of spring member 10. Each of the

shims

12 and 13 are preferably made from a substantially non-magnetic material such as stainless steel.

The armature piece 11, which is secured to the free end of the spring member 10, is shown in an S-shape so as to complete the magnetic gap 16 between pole piece 8 at one end of the armature 11, and at the same time to provide a surface for movable contact 17 at the other end of armature piece 11. In order to enhance the current carrying characteristics of the switch at the magnetic gap 16, when this gap is closed as shown in FIGURE 3, the adjacent surfaces 19 of pole piece 8 and armature piece 11, which make up the gap 16 may be plated, for example with gold. As in the case of pole piece 8, the armature piece 11 is made from a magnetic material such as No. 45 Permalloy. Completing the elements of armature assembly 9 is spring support 18 which is a plate adjacent spring member at the contact 17 end thereof. Support 18 is principally used to aid in the mechanical union of the armature piece 11 with spring member 10.

The fixed contact 22 is adjacent movable contact 17 and secured to the lead 3. Each of the

contacts

17 and 22 uses a material which becomes a matter of design in accordance with the requirements for the switch; while the shape of one or both of the surfaces on the

contacts

17 and 22 is preferably curved as shown in FIGURES 1-4. Examples of contact materials are tungsten, silver and cadmium including combinations thereof.

To operate the switch of this invention when in the position of FIGURE 1, i.e. the normally-open position, an external magnetic field supplied, for example, by a coil or a permanent magnetic field adjacent to and preferably surrounding the tube 1, is applied at the area of the magnetic gap 16. The resulting magnetomotive force must be sufficient to overcome the spring force of spring member 10 after which the armature piece 11 pivots on spring member 10 since armature piece 11 is attracted magnetically to pole piece 8 at the magnetic gap 16. This spring force of spring member 10 can be equated to its retractile force or that force necessary to be overcome and thereby close the contacts 17 and 22 (FIGURE 2) and can then be equated to the contact force between

contacts

17 and 22 when considering the spring force necessary to fiex spring member 10 and thereby move the armature 11 from the FIGURE 2 to the FIGURE 3 position, i.e. complete closure of the magnetic gap 16.

In order to further control the particular magnetomotive force necessary to move armature 11, the inner shim 12 may be varied in length so as to select a desired pivot point for and effective length of the spring member 10. The force to be overcome in spring member 10 is thereby adjusted. Still further control is affected by varying the length of outer shim 13 to thereby apply necessary restriction to flexure of spring member 10 which is a function of spring force. The roll of

shims

12 and 13 will be further discussed below.

As will be seen in FIGURE 2, the steps of switch closing call for the

contacts

17 and 22 to close before the magnetic gap 16 has closed. Thus, switch closing consists of a continuous closing motion comprising two sequential steps, the second of which is shown in FIGURE 3. In order that this two step closing along with its purpose will be more clear, indicator lines have been added to the contacts in FIGURES 2 and 3, i.e. indicator line 25 has been added to contact 17 and indicator line 26 has been added to contact 22. The apparent continuity between each

indicator line

25 and 26 in FIGURE 2 illustrates the relative position of the

contact

17 and 22 at the first step of the closing process, i.e. when the

contact

17 and 22 first meet. The

same indicator lines

25 and 26 are shown by FIG- URE 3 as a discontinuous path after the magnetic gap 16 has closed.

It is evident that the switch closing motion between the positions shown in FIGURES 2 and 3, which motion constitutes the second step of the closing process, has caused the movable contact 17 to slide along the surface of fixed contact 22. This relative contact movement or contact wiping is made available through the resiliency or flexure of spring member 10 and becomes an important feature of this invention. This importance is especially evident when higher currents are to be carried by the switch since contact wiping establishes a shear as well as tension force on welds should they exist between the

contacts

17 and 22. As is well-known in the art, these welds become more probable as the current carried by a switch increases.

Once the gap 16 has been closed, the reluctance of the energizing magnetic circuit is reduced such that less magnetomotive force is necessary to retain the switch in the closed position of FIGURE 3. This phenomenon permits practical application of well-known latching permanent magnets (not shown) adjacent the gap 16 so as to hold the switch closed after removal of the closing mag- 4 netomotive force. By using polarized signals, the switch, latched by permanent magnets, can be opened by inducing a flux which opposes the latching flux to thereby neutralize the necessary latching magnetomotive force.

Opening of the switch shown in FIGURE 3 results from the sufficient removal of the external magnetic field holding the switch closed and consequently a reversal of the two step closing process described above. That is, without a sufiicient magnetomotive force, the spring force of spring member 10 pivots the armature piece 11 so as to first open the magnetic gap 16 and slide contact 17 along contact 22 until the position of FIGURE 2 is reached; after which, the continued pivotal movement of armature piece 11 separates the contact 17 from fixed contact 22. and returns the switch to the position of FIGURE 1. Control over this spring force of spring member 10 can be obtained by not only varying the length of outer shim 13 to thereby vary the pivot point and the degree of available flexure of spring member 10, but also by varying the width and thickness of the spring member 10.

It is important in a switch of this kind to have contact force between contacts,

e.g. contacts

17 and 22, sufficient to insure low contact resistance when the switch is in the closed position of FIGURE 3. This desired contact force is accomplished through the particular structure of this invention including spring member 10 biasing armature piece 11 which connects the separate magnetic gap 16 and the electrical gaps between

contacts

17 and 22. Specifically, when contact 17 first meets contact 22 during switch closing, a contact force therebetween is established and is proportional to the magnetomotive force at gap 16 which force has been transferred to contact 17 through armature piece 11 pivoting with spring member 10. Further movement of armature piece 11, viz. closure of gap 16 and sliding of contact 17 upon contact 22, increases the contact force between

contacts

17 and 22 proportionally to that increase in magnetomotive force at gap 16 which is necessary to overcome the spring force of spring member 10. Once the gap 16 closes, the maximum contact force between

contacts

17 and 22 has been established.

Since the contact force is a function of spring force, the material used in spring member 10 becomes a significant design variable as does the length of

shims

12 and 13. For example, the length of inner shim 12 varies the effective length of spring member 10 and the pivot point for armature piece 11 to thereby determine spring force.

'The length of outer shim 13 affects the spring force during the first step of closing by controlling the flexure of spring member 10 and during the second step of closing by varying the external force, e.g. magnetomotive force at gap 16, necessary to flex spring member 10 as contact 17 slides along contact 22. With this available spring force adjustment, the switch of this invention may be readily designed for desired as well as maximum contact force, which versatility is considered to be a significant contribution.

Besides providing for a contact force whenever

contacts

17 and 22 are closed, the switch construction of this invention furthercauses the contact force to remain constant essentially throughout the opening or break period of the switch. It is to be recalled that the magnetomotive force necessary to retain the magnetic gap 16 in a closed condition is both substantially less than that force which is necessary to close the gap 16 and proportional to the contact force. Upon the initiation of switch opening, collapse of that external magnetic field which was necessary to close the switch will not influence the magnetic gap 16 (and consequently contacts 17 and 22) which remain closed during the initial and substantial portion of field collapse. However, once the spring force of spring member 10 overcomes the decreasing magnetomotive force of the collapsing field, the magnetic gap 16 opens and the contact force at

contacts

17 and 22 diminishes to zero contact force as

contacts

17 and 22 separate. The period of time during which the

contacts

17 and 22 remain closed after the opening of the magnetic gap 16, Le. the increment of time during which armature piece 11 moves from the position of FIGURE 3 to that of FIGURE 2, is insignificant when compared with the time during which the switch remains closed while the external field collapses. Thus, it can be said that the contact force remains constant essentially throughout the opening or break period of the switch.

It should be noted that the use of latching magnets to bias the gap 16 closed would reduce the relative time for field collapse from the initiation of switch opening until the

contacts

17 and 22 open since the magnetomotive force of such a magnet is more nearly that of the magnetomotive force necessary to overcome the opposing spring force of spring member 10. Nevertheless, the rela tive time increment during which gap 16 opens is again such that the contact force can be said to be constant essentially throughout the break period.

The relationship between the magnetomotive force and the contact force available through the cantilever construc tion of armature assembly 9 also results in a snap. action or a positive closing which is significant, particularly under higher current carrying conditions. By selecting an external magnetic field at gap 16, which is sufiicient to move the armature piece 11 through the two closing steps shown in FIGURES 2 and 3, the armature piece 11 will move toward closing with a snap motion and will not come to rest until the switch is closed as in FIGURE 3. This snap closing action is very important as it assures positive closing as well as reducing contact bounce and the undesirable elfects therefrom at closing; the latter being aided in the case of this invention by the wiping action between

contacts

17 and 22. Snap action also exists upon switch opening or the break period as the armature moves away from a closed position wtih a snap action. This snap action thereby aids in the assurance of separation between

contacts

17 and 22 and is available through the unique armature assembly construction which provides necessary spring force in spring member 10.

Achieving snap action upon switch closing requires that the magnetomotive'force exceed the spring force at all times during the closing of gap 16. As has been pointed out above, the spring force is a function of desired contact force. Thus, there becomes evident a necessary compatibility of spring and shim construction with magnetic gap size and magnetomotive source size in orderto achieve desired results. Herein lies a still further contribution of the invention in that the gap between

contacts

17 and 22 may be independently varied in order to aid in achieving both the desired snap action and contact force. For example, before sealing the tube 1 around lead 2, the lead 2 and predajusted assembly 9 can be moved so that a contact gap size can be selected which will complement the particular characteristics of the armature assembly 9. Variation of the necessary magnetomotive force may also enter into this contact gap selection. This means simple switch assembly and adjustment are available for a switch structure which incorporates an advantageous plurality of structural variables.

One method of switch assembly includes sealing one lead, e.g. lead 3, with tube 1. The opposite end of tube 1 remains open. Armature assembly 9 is adjusted so as to provide both a selected magnetic gap 16 and a selected spring force in spring member 10 (by means of

shims

12 and 13 as outlined above). Assembly 9 with lead 2 is then inserted into the open end of tube 1 so as to establish a contact gap between

contacts

17 and 22.

Before sealing the tube 1 and lead 2, it is possible to .establish desired switch performance, e.g. both the desired snap action and contact force as described above, by adjusting the gap size between the

contacts

17 and 22 through movement of the assembly 9. It is important that the contact gap be properly selected since, for example, a contact gap which is too small could prevent snap action while a contact gap which is too large could deny closing between

contacts

17 and 22. It should be noted that contact force would be necessarily increased with the final closing of magnetic gap 16 should the

contacts

17 and 22 be too close; but this increased contact force exists at the expense of other desired characteristics such as snap action. Moving the assembly 9 in a selected magnetic field there about until snap action occurs, i.e. both the contact gap between

contacts

17 and 22 and the magnetic gap 16 close, has been used to successfully determine the desired contact gap. The tube 1 is then sealed at the lead 2.

It should be noted that the separation of the magnetic gap 16 from the gap between the

electrical contacts

17 and 22 increases current capacity of the resulting switch construction. Specifically, the

contacts

17 and 22 can be made of material which will accommodate a higher current without interfering with the magnetic conductivity necessary to close the switch. Furthermore, the use of a separate magnetic gap 16 in the switch of this invention permits shunting the spring as a current carrying conduit when the switch is in its closed position. As has been pointed out above, the surfaces 19 on pole piece 8 and armature piece 11 which are immediately adjacent to the magnetic gap 16 are preferably plated so as to enhance the electrical conductivity when the magnetic gap 16 is closed. The availability of such a shunt permits hitherto unavailable flexibility in selecting the material to be used in spring member 10. As has also been pointed out above, the flexibility is important when selecting a spring to provide desired contact force. A further advantage is illustrated in the fact that without the shunt it would be necessary to use an alloy such as beryllium-copper in spring member 10 so as to carry the higher current; but the use of berylliunncopper causes disadvantages such as increased time and expense in manufacture which is not the case when a material such as spring steel is used. Moreover, spring steel has the advantages of higher strength and fatigue life.

The embodiment of FIGURE 4 is included to illustrate one of the many variations to which the switch of FIG- URES 1-3 is susceptible. As is evident, those parts of switch in FIGURE 4 which are common to the switch structure of FIGURES 1-3 have identical reference numerals. Added to this previously described structure is contact 31 which is secured to the armature piece 11 and a contact 32 which is secured to a third lead 33 so that a form C switch evolves with lead 2 acting as a common.

The switch of FIGURE 4 operates in the same manner as previously described for FIGURES 1-3 but with contacts 31 and 32 being separated with the pivoting movemerit of armature piece 11 and closing again when the armature assembly 9 returns to its normally-open position.

With the exception of leads 2 and 3 which are round in cross-section, the remaining elements, viz pole piece 8, shims 12 and 13 plus the armature assembly 9, are each esssentially rectangular in cross-section.

The selection of the atmosphere to be found within a sealed switch utilizing an enclosure such as tube 1 depends upon several variables including the particular material to be used in the electric contacts, e.g. 17 and 22. Because of the research and development which accompanied the switch of this invention, it can now be concluded that the particular atmosphere selected for a sealed switch can affect and thereby prevent sticking between the abutting surfaces at the magnetic gap 16. This sticking generally results after repeated closing and opening of the magnetic gap and is especially significant in atmospheres of hydrogen, the inert gases such as helium, neon, argon, krypton and xenon, and in an atmosphere made of a vacuum.

This concept of properly selecting an atmosphere for a sealed switch to thereby prevent sticking at the magnetic gap is exemplified by an atmosphere comprising hydrogen to which nitrogen is added in order that the sticking will be eliminated. Additionally, an atmosphere made of a vacuum diminished by nitrogen, has satisfactorily prevented magnetic gap sticking. Additives other than nitrogen may be used, such as oxygen, sulfur and compounds thereof; but as with nitrogen, the use and amount of such additives must take into account the effect these atmospheres will have on switch performance, e.g. the atmospheres arc suppression capabilities and tendency to form harmful films on the contact surfaces. In this regard, nitrogen contents of at least about 1% by volume in hydrogen, the inert gases or a vacuum have successfully eliminated magnetic gap sticking without substantially affecting switch performance.

The use of gases such as hydrogen or the inert gases for the atmosphere to be enclosed within tube 1 provides 7 additional advantages in that higher pressures, eg 1 to 15 p.s.i.g. can be used. These higher pressures result in corresponding increases in breakdown voltages. On the other hand, lower pressures can provide desired advantages through the less destructive arcing which results.

With modification, the switch of this invention will accommodate still higher current capacity; For example, parallel leads with a common connection to the switch or a lead made of concentric sections with the inner section capable of accommodating higher current would improve current capacity. Selected materials for parts such as spring member 10 and armature 11 will also permit increased current capacity for the switch.

I claim:

1. A sealed switch which responds to a magnetic field comprising:

(a) magnetic means electrically connected to a first lead,

(b) armature means carrying a first contact means and forming a magnetic gap with said magnetic means,

(c) said armature and magnetic means being responsive to said magnetic field at said gap, 7

(d) second contact means associated with said first contact means and electrically connected to a second lead,

(e) resilient means biasing said armature means to a gap-open position,

(f) said resilient means electrically connected to said first lead,

(g) said magnetic means and armature means acting to electrically shunt said resilient means when said gap is closed, and

(h) substantially non-magnetic means interposed between said first lead and said resilient means.

2. The switch of claim 1 wherein said non-magnetic means comprise shim means.

3. A sealed switch which responds to a magnetic field comprising:

(a) magnetic means electrically connected to a first lead,

lb) pivoted armature means carrying a first contact means, forming a separate magnetic gap with said :magnetic means and pivoted at a selected point between but including said first contact and said ((c) said armature and magnetic means being responsive to said magnetic field at said gap,

(d) second contact means associated with said first contact means and electrically connected to a second lead, and

(e) cantilever resilient means with a spring force biasing said armature means in a gap-open position to thereby cause said armature means to mechanically transfer magnetomotive force derived from said field to said contacts as a contact force, said magnetomotive force being proportional to but greater than said spring force.

4. A sealed swtich which responds to a magnetic field comprising:

8 (a) magnetic means electrically connected to a first lead, (b) armature means carrying a first contact means forming a magnetic gap with said magnetic means and pivoted at a selected point between but including said first contact and said gap,

(c) said armature and magnetic means being responsive to said magnetic field at said gap,

(e) resilient cantilever means carrying said magnetic armature means at a point separated from said gap to bias said armature means in a gap-open position,

(f) said resilient cantilever means connected to said magnetic means by intermediate non-magnetic shim means,

(g) said shim means located adjacent said resilient cantilever means to establish a pivot point intermediate said first contact and said gap and thereby cause said armature means to mechanically transfer magnetomotive force derived from said field to said contacts as a contact force, and

(h) said magnetic means and magnetic armature means acting to electrically shunt said resilient means when said gap is closed.

5. The switch of claim 4 wherein said resilient means is connected to said magnetic armature means so that said first contact will move along the surface of said second contact after said contacts have closed.

6. The switch of claim 5 wherein said resilient means carries said magnetic armature means so that contact surfaces of said first and second contacts meet at an angle.

7. The switch of claim 4 wherein said shim means include means to vary the spring force of said resilient means.

8. A sealed switch which responds to a magnetic field comprising:

(a) magnetic means electrically connected to 'a first lead,

(b) pivoted armature means carrying a first contact means and forming a separate magnetic gap with said magnetic means,

((1) second contact means associated with said first contact means and electrically connected to a second lead,

(e) cantilever resilient means with a spring force biasing said armature means in a gap-open position to thereby cause said armature means to mechanically transfer magnetomotive force derived from said field to said contacts as a contact force, said magnetomotive force being proportional to but greater than said spring force, and

(f) shim means adjacent said resilient cantilever means so as to determine an armature pivot point and said spring force.

9. A sealed switch which responds to a magnetic field comprising:

(a) magnetic means electrically connected to a first lead,

(b) pivoted armature means carrying a first contact means, forming a separate magnetic gap with said magnetic means and pivoted at a selected point between but including said first contact and said (c) said armature and magnetic means being responsive to said magnetic field at said gap,

(e) cantilever resilient means biasing said armature means in a gap-open position to thereby cause said armature means to mechanically transfer magneto- 9 motive force derived from said field to said contacts as a contact force.

10. A sealed switch which field comprising:

(a) magnetic means electrically connected to a first lead,

(e) cantilever resilient means biasing said armature means in a gap-open position to thereby cause said armature means to mechanically transfer magnetomotive force derived from said field to said contacts as a contact force, and

responds to a magnetic (f) shim means adjacent said resilient cantilever means so as to determine an armature pivot point.

References Eited by the Examiner UNITED STATES PATENTS 1,185,240 5/1916 Petersen 200-87 2,481,003 9/1949 Curtis 200-87 X 2,485,024 10/1949 Vale et a1. ZOO-87 2,993,104 7/1961 Zimmer 200-87 X 3,005,072 10/1961 Brown 200-87 3,018,353 1/1962 Mitchell 200116 3,070,677 12/1962 Lowry 20087 3,147,538 9/1964 Perkins 20087 X 5/1965 Juptner 29-155.55

BERNARD A. GILHEANY, Primary Examiner.

I. I. BAKER, Assistant Examiner.

Claims

1. A SEALED SWITCH WHICH RESPONDS TO A MAGNETIC FIELD COMPRISING: (A) MAGNETIC MEANS ELECTRICALLY CONNECTED TO A FIRST LEAD, (B) ARMATURE MEANS CARRYING A FIRST CONTACT MEANS AND FORMING A MAGNETIC GAP WITH SAID MAGNETIC MEANS, (C) SAID ARMATURE AND MAGNETIC MEANS BEING RESPONSIVE TO SAID MAGNETIC FIELD AT SAID GAP, (D) SECOND CONTACT MEANS ASSOCIATED WITH SAID FIRST CONTACT MEANS AND ELECTRICALLY CONNECTED TO A SECOND LEAD, (E) RESILIENT MEANS BIASING SAID ARMATURE MEANS TO A GAP-OPEN POSITION, (F) SAID RESILIENT MEANS ELECTRICALLY CONNECTED TO SAID FIRST LEAD, (G) SAID MAGNETIC MEANS AND ARMATURE MEANS ACTING TO ELECTRICALLY SHUNT SAID RESILIENT MEANS WHEN SAID GAP IS CLOSED, AND (H) SUBSTANTIALLY NON-MAGNETIC MEANS INTERPOSED BETWEEN SAID FIRST LEAD AND SAID RESILIENT MEANS.