US3602851A

US3602851A - Magnetic time delay switch

Info

Publication number: US3602851A
Application number: US25195A
Authority: US
Inventors: John R Wiegand
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-04-02
Filing date: 1970-04-02
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31

Abstract

A magnetic reed switch comprises an insulative housing in which are laterally spaced magnetic reeds. A coil of magnetic wire is wound around the housing. An adjustable clamp encircles the coil. The reeds, coil and clamp can be connected in a circuit to perform a time delay switching function which is variable over a wide range by adjustably positioning the clamp.

Description

United States Patent Patented 361m 11. Wiegnnd as: Bllfillll' $1., Valley Stream, N.Y. 11580 25,195

Apr. 2, 1970 Aug. 31, 1971 Inventor Appl. No. Filed MAGNETIC TIME DELAY SWITCH 10 Claims, 4 Drawing Fig.

us. c1. 335/146,

317/133, 335/154, 336/179 161.01 11011161/04 Field ofSearch 317/133;

[ References Cited UNITED STATES PATENTS 3,003,019 11/1961 Scheidig 335/208 3,174,008 3/1965 Mishelevich et al. 335/154 3,284,735 11/1966 Siiberg 335/208 X Primary Examiner-Bernard A-. Gilheany Assistant Examiner-R. N. Envall, Jr. AttorneyPolachek & Saulsbury ABSTRA CT: A magnetic reed switch comprises an insulative housing in which are laterally spaced magnetic reeds. A coil of magnetic wire is wound around the housing. An adjustable clamp encircles the coil. The reeds, coil and clamp can be connected in a circuit to perform a time delay switching function which is variable over a wide range by adjustably positioning the clamp.

MAGNETIC TIMEDELAY swrrcn I This invention relates to the artof time delay circuit devices and more particularly concerns a magnetic timedelay switch which is variable in time delay over a wide range.

- The most common devices currently used for performing time delay switching functions employ either a thermally activated bimetallic strip .or a solid-state circuit. The electronic time delay devices are employed where specifications are quite stringent as in military and space flight equipment. Forgeneral industrial or commercial applications bimetallic ele- I the two contacts finally separate, thereby breaking the circuit.

-' For a number of reasons it is desirable to replace this kind of device with a radically differentconfiguration. The typical delay unit is a rather inefficient device. Normally the fullpower source voltage is placed across the heatingelement, in parallel to the load. Enough energy must be pumped into the bimetallic element to very significantly raise its temperature. Furthermore, the action of opening (or closing) a set of contacts is by its very nature slow, giving the problem of possible arcing and brief periods of indeterminate switch positions.

' Mechanical means can be employed to cause the contacts to snap, and this further adds to the complexity. The assembly of this thermostatic delay requires precision, to insure that proper shape and positioning of the two metals to be joined are accurate. This does not lend itself very easily to a range of adjustments. It also does not lend itself to miniaturized packaging. Of ten the whole device is enclosed in a case with a plug-in base, such as a tube. This is too bulky for many applications, and also may require that extra wiring be run from a pushbutton or switch which is'located at a distant point more ing or direct current operation and can work off power lines of readily available voltages such as 12, 24 or 117 volts AC or DC. Production costs are significantly less than those of other types of time delay switches. The use of bimetallic strips is avoided. Also eliminated are mechanical means for snapping contacts apart or together, resistors, capacitors, rectifiers,

transistors or any other solid-state or electronic tube components. Furthermore efficiency is improved over that attainable by use of thermally responsive bimetallic strips or electronic circuit-type time delay units. A further very important advantage is that the amount'of time delay is adjustable over a wider range than is possible with comparable conventional time delay units. I

Other and further features, objects and advantages will become apparent from the following detailed description taken together with the drawing, wherein:

FIG'. I is an oblique side view of a time delay switch embodying the invention.

F IG. 2 is an enlarged cross-sectional view.

FIG. 3 is a longitudinal sectional view taken on line 3-3 of FIG. 2;

, FIG. 4 is a diagram of an electrical circuit embodying the invent-ion.

7 Referring first to FIGS. 1 2 and 3, the switch 10 comprises a tubular closed housing 11 made of electrically insulative material such as glass or a suitable plastic. The housing is axially elongated andhas a thin cylindrical wall 12 closed at

opposite ends

14, 16. Two

reeds

18 and 20 made of magnetic material are longitudinally secured in the housing at ends l4, 16. Free

inner ends

19, 21 of the reeds are laterally spaced from each other but overlap slightly axially of the housing.

Outer ends

22, 24 of the reeds extend beyond the closed, sealed ends of the housing. The reeds are flexible but sufficiently'and massive so that they do not make contact with each other for normal conditions of vibration and shock. When a magnetic force of sufficient intensity is applied the reeds can be brought together at their overlapped free ends. Removal of the magnetic influence will allow the reeds to spring-apart and assume their normal spaced position shown in FIGS. 2 and 3. In a practical application the reeds may be about 2 inches in overall length and the housing 11 may also be about 2 inches.

A magnetic wire made of iron-nickel or other suitable alloy is wound in a single layer-to form a coil25 around the housing 11 extending from one end to the other of the cylindrical wall 12. One end 26 of the coil is secured by solder 28 to end portion 22 of reed 18. The other end 29 of the coil is left free. An electrically conductive cylindrical clamp 30 encircles the coil and housing. Radially extending tabs 32 are abutted and secured together by a screw 33. The clamp'30 can be moved axially of the coiland housing by loosening the screw. Tightening the screw locks the clamp in place on the coil and housing. The location of the clamp axially long the coil determinesthe time delay action of the switch.

End portions

22 and 24 of the reeds andclarnp 30 may be further connected by

wires

32, 34, 36 to external circuitry such as shown diagrammatically inFIG. 4. Screw 33 will hold wire 36 while

solder joints

38, 39 will hold

wires

32, 34.

FIG. 4 shows a manually operated'and activated time delay circuit 50. A pushbutton switch 52 which is normally open, is

' connected to the end portions of the reeds via

wires

32 and 34 and bridges the reeds electrically when the pushbutton is pressed. When the pushbutton switch is closed, the external connected to end portion 24 of reed 20. The circuit 16 is connected by

wires

36 and 56 in series" with an external load device 60 which maybe a lamp, resistor, or the like, and

terminals

62, 63 of a suitable electrical power source 64. The load and be any device to which it is desired to apply power for a predetermined length of time after operating the, pushbutton switch 52. The impedance of the magnetic coil 25 will be small with respect to that of the load device 60.

In operation of the circuitry of FIG. 4, when the pushbutton switch 52 is closed by pressing the pushbutton, current flows from the power source 64 via

terminals

62, 63 through load device 60, wire 36, clamp 30, through a portion of coil 25 located between clamp 30 and reed end portion 22, through wire 32, pushbutton switch 52, wire 34, reed end portion 24 and wire 56. The voltage developed across the magnetic coil 25 between the clamp 30 and wire 32 small with respect to the voltage across the load 60 or that of power source 64. The electrical current flowing through coil 25 causes a magnetomotive force field to be developed along the main axis of the coil and housing. The magnetic reeds in the housing channelize the magnetic flux because of their low permeability, except for at the small discontinuity at the airgap G between the reeds. The same current also creates miniature flux paths within the .wire coil itself. The magnetomotive force field between two free ends of the reeds develops a mechanical force which tends to pull them together as indicated by arrows, A, B. As soon as the

reed end

19, 21 contact each other they effectively short circuit the pushbutton switch 52 which may now be manually released to return to its normally open position. The current passing through the reeds I8, 20, in turn,

applies a magnetomotive force to the wire coil 25. Power will now be maintained in the load via the contacting inner end portions of the reeds.

The external circuit will not remain closed indefinitely. The time duration the external circuit will remain closed and power will be supplied to load device 60 will depend on the time delay characteristic of the switch 10. This time delay characteristic depends primarily on the diameter of the wire coil 25, the position of the clamp 30 along the coil, and the impedance of the load device. The characteristic depends only secondarily on the ambient temperature of the switch 10. Despite the small percentage amount of power dissipated in the turns of coil 25 it is enough to slowly raise the temperature of the coil. This increase in temperature has its effect on a molecular level. Much of the alignment of the magnetic domains in the wire of the coil 25 is destroyed during the heating. The magnetomotive force along the main axis of the housing 11 decreases significantly. This force had originally been just sufficient to close the contacts between the inner ends of the reeds. Now, however, there is hysteresis to overcome. Since the reeds are touching, significantly less flux density still provides more than adequate force to keep the inner reed ends 19,21, pressed together and allows the current to flow between the outer reed ends 22, 24, since the necessary force is inversely proportional to the separation between the reeds. However, as long as the current is so flowing the temperature continues to rise. The change in the net magnetomotive force field will not be linear, but rather the complex interactions of the fields will cause a self-eliminating feedback type of interaction. Soon a point will be reached where the diminished flux density no longer induces a force sufficient to overcome the entire tension no longer induces a force sufficient to overcome the entire tension in the

reeds

18, 20. As the inner ends 19, 21, of the reeds begin to separate, the electrical resistance through the reeds between ends 22, 24, increases rapidly causing through collapse of the magnetic fields thereby further reducing the holding force the reed ends 19, 21, at an extremely rapid rate. The force inherent in the tension of the reeds causes the

ends

19, 21, of the reeds to snap apart. The circuit is broken and current flow stops. The switch starts to cool rapidly. The time delay cycle has been completed. The length of this cycle is the time interval between opening pushbutton switch 52 and opening of contact between reed ends 19, 2]. Throughout the entire cycle of operation the temperature never rises above 100 F. or so, so that the switch is never too hot to touch at any point. The arrangement of the circuitincluding switch 10 and pushbutton switch 52 will be very compact to occupy very small volume.

The above description of operation applies particularly to direct current operation. When alternating current is supplied by power source 64, a permanent magnet 70 will be provided. This magnet will be movably disposed adjacent the switch coil 25 to provide the magnetomotive force referred to above. The magnet may be coupled to the pushbutton switch so as to be moved into effective magnetomotive force inducing position only when the pushbutton switch is closed. When the pushbutton is opened the magnet will be withdrawn beyond its effective magnetomotive force inducing position. Otherwise operation of the circuitry will be same as described above. The voltage developed across the portion of coil 25 between clamp 30 and reed end 22 will be primarily due to the resistance of the wire of coil'25 rather than its inductive reactance when AC current is employed.

To summarize, the invention has the following desirable features:

l. The magnetic switch assembly performs a switching function with predetermined time delay.

2. The time delay characteristic can be adjusted in time duration over a wide range.

3. The time delay switch assembly can be constructed from a few simple inexpensive components.

4. The basic components of the time delay switch assembly comprise an insulative housing, a pair of magnetic reeds, a coil of magnetic wire, and cylindrical clamp.

5. The components of the assembly require only a very simple assembly procedure.

6. The time delay switch assembly may include a small pushbutton switch in a time delay switching circuit.

7. The time delay switching circuit will be compact and occupy a very small space. i y

8. The time delay switching circuit need have only two external terminals.

9. The small size, small number of terminals and simplicity of construction enable the circuit to be used in many applications heretofore unable to use conventional time delay devices.

10. The time delay switching circuit will maintain power to a load device when series connected to the load and a power source, once the circuit is activated, for a predetermined duration of time.

1 l. The device consumes so very little power that the load device consumes substantially all the power supplied by the power source.

12. The time delay switching circuit has the inherent characteristic of removing power from the load instantaneously so that there is no indeterminate state between power-on and power-off.

13. The temperature of the time delay switch assembly never becomes too hot to handle manually.

14. The time delay switch assembly can operate in any desired orientation or physical position.

15. The time delay switch assembly can be made to operate with an AC or DC power source.

16. The time delay switch assembly will operate with a wide range of applied line voltages.

17. The time delay adjustment is very easily and simply made by slidably adjusting the clamp along the magnetic switch.

18. The time delay switching circuit can operate with predetermined time delay for different loads by adjusting the position of the clamp along the magnetic switch.

19. The assembly tolerances of the reeds need not be as critical as those of comparable bimetallic elements employed in time delay devices.

20. The time delay switch assembly will be highly reliable and certain in operation.

What is claimed is:

l. A time delay switching device, comprising a cylindrical insulative support; a helical coil of magnetic wire wound on said support; said coil wire composed of material which loses its magnetic permeability upon heating a pair of flexible magnetic reeds secured to opposite ends of said support and extending longitudinally inside said support, said reeds having inner overlapping laterally spaced free inner ends, said reeds having outer ends extending outwardly of opposite ends of said cylindrical support, the outer end of one reed being connected to one end of said coil, the other end of said coil being free; and a conductive member mounted on said support and slidable along said coil in contact therewith, and means for connecting said conductive member and the outer end of the other one of said reeds is series with a source of electrical voltage and a resistive load, whereby momentary electrical connection of the outer ends of said reeds will pass electrical current through a part of said coil to generate a magnetomotive force, which causes said inner ends of the reeds to contact each other, and whereby opening said electrical connection will leave said inner ends of the reeds contacting each other for a certain time duration while power is supplied to said load, whereupon said magnetomotive force will decrease due to current through said coil, which causes heating thereof, until the contacting inner ends of the reeds separate and cut off the power supplied to said load.

2. A time delay switching device as defined in claim 1, further comprising a switch having normally open contacts respectively connected to the outer ends of the reeds, whereby closure of said switch to close said contacts establishes said electrical connection between the outer ends of the reeds.

3.-A time delay switching device as defined in claim 2, wherein said switch is a manually operable pushbutton switch.

4. A time delay switching device as defined in claim 1, wherein said conductive member has the form of a cylindrical clamp encircling said support and coil in Contact with the coil, whereby said certain time duration is determined by the position of said clamp axially along the coil. I

5. A time delay switching device as defined in claim 4 further comprising a switch having normally open contacts respectively'connected to the outer ends of the reeds, whereby closure of said switch to close said contacts establishes said electrical connection between the outer ends of the reeds.

6. A time delay switching device as defined in claim 1, further comprising an electrical voltage source and a resistive load connected in series circuit with each other, said circuit having two terminals respectively connected to said conductive member and said outer end of the other one of the reeds, said coil having an impedance which is smaller that that of said load so that substantially all of the power generated by said voltage source is consumed in said load.

7. A time delay switching device as defined in claim 6, wherein said voltage source supplies alternating current to the load and coil, said device further comprising a permanent magnet movable disposed adjacent said coil for generating a magnetomotive force field between the spaced inner ends of the reeds when the magnet is momentarily disposed sufficiently close to the coil to cause said inner ends of the reeds to contact eachother.

8. A time delay switching device as defined in claim 5, further comprising an electrical voltage source and a resistive load connected in series circuit with each other, said circuit having two terminals respectively connected to said clamp and the outer end of said other one of the reeds, said coil having an impedance which is smaller than that of said load so that substantially all of the power generated bysaid voltage source is consumed in said load.

9. A time delay switching device as defined in claim 8,

wherein said switch is a manually operable pushbutton switch. 1

10. A time delay switching device as defined in claim 9, wherein said voltage source supplies alternating current to the load and coil, said device further comprising a permanent magnet movable disposed adjacent said coil for generating a magnetomotive force field between the spaced inner ends of the reeds when the magnet is momentarily disposed sufficiently close to the coil to cause said inner ends of the reeds to contact each other.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 602 851 Dated August 31 197].

Inventor(s) John R. Wiegand It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 44 after "terminals" insert "at wire 36 and" Column 2, line 50 and be" should read can be" Column 3, lines 31 34 after "entire tension" delete "no longer induces a force sufficient to overcome the entire tension" appearing after "entire tension" Column 3, line 36 "through" should read "instant" Column 3, line 38 insert between after holding force" Column 3, line 58 insert switch after "pushbutton" Column 5, Claim 7, line 22 "moveable" should read "moveably" Column 6, Claim 10, line 17 "moveable" should read "moveably" Signed and sealed this 17th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHJ:;R,JR. ROBERT GOTTSCI-LALK Attestlng Officer Commissioner of Patents

Claims

1. A time delay switching device, comprising a cylindrical insulative support; a helical coil of magnetic wire wound on said support; said coil wire composed of material which loses its magnetic permeability upon heating a pair of flexible magnetic reeds secured to opposite ends of said support and extending longitudinally inside said support, said reeds having inner overlapping laterally spaced free inner ends, said reeds having outer ends extending outwardly of opposite ends of said cylindrical support, the outer end of one reed being connected to one end of said coil, the other end of said coil being free; and a conductive member mounted on said support and slidable along said coil in contact therewith, and means for connecting said conductive member and the outer end of the other one of said reeds is series with a source of electrical voltage and a resistive load, whereby momentary electrical connection of the outer ends of said reeds will pass electrical current through a part of said coil to generate a magnetomotive force, which causes said inner ends of the reeds to contact each other, and whereby opening said electrical connection will leave said inner ends of the reeds contacting each other for a certain time duration while power is supplied to said load, whereupon said magnetomotive force will decrease due to current through said coil, which causes heating thereof, until the contacting inner ends of the reeds separate and cut off the power supplied to said load.

3. A time delay switching device as defined in claim 2, wherein said switch is a manually operable pushbutton switch.

4. A time delay switching device as defined in claim 1, wherein said conductive member has the form of a cylindrical clamp encircling said support and coil in contact with the coil, whereby said certain time duration is determined by the position of said clamp axially along the coil.

5. A time delay switching device as defined in claim 4 further comprising a switch having normally open contacts respectively connected to the outer ends of the reeds, whereby closure of said switch to close said contacts establishes said electrical connection between the outer ends of the reeds.

7. A time delay switching device as defined in claim 6, wherein said voltage source supplies alternating current to the load and coil, said device further comprising a permanent magnet movable disposed adjacent said coil for generating a magnetomotive force field between the spaced inner ends of the reeds when the magnet is momentarily disposed sufficiently close to the coil to cause said inner ends of the reeds to contact each other.

8. A time delay switching device as defined in claim 5, further comprising an electrical voltage source and a resistive load connected in series circuit with each other, said circuit having two terminals respectively connected to said clamp and the outer end of said other one of the reeds, said coil having an impedance which is smaller than that of said load so that substantially all of the power generated by said voltage source is consumed in said load.

9. A time delay switching device as defined in claim 8, wherein said switch is a manually operable pushbutton switch.