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Publication numberUS3794811 A
Publication typeGrant
Publication dateFeb 26, 1974
Filing dateJul 19, 1972
Priority dateApr 11, 1970
Also published asDE2137285A1, DE2137285B2, DE2137285C3
Publication numberUS 3794811 A, US 3794811A, US-A-3794811, US3794811 A, US3794811A
InventorsHehl K
Original AssigneeHehl Karl
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Automatic safety switch member
US 3794811 A
Abstract
An automatic safety circuit for monitoring the power switching means controlling the main current circuit to an electric power load to automatically cut off the current in the event of a malfunction of the power switching means which causes it to continue to remain in its closed condition. The auxiliary switching circuit includes a switching arrangement for selectively disrupting the main current circuit, the switching arrangement being composed of a heatable switching element, an electrical resistance heating element formed as a coil which concentrically encloses the heatable switching element and an electrically insulating supporting sleeve which supports the coil and is disposed coaxial to the heatable switching element.
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Description  (OCR text may contain errors)

United States Patent [191 Hehl 1*Feb. 26, 1974 1 AUTOMATIC SAFETY SWITCH MEMBER [76] Inventor: Karl Hehl, Siedlung 183, D-7291 Lossburg, Germany Notice: The portion of the term of this patent subsequent to Oct. 1, 1989, has been disclaimed.

[22] Filed: July 19, 1972 [21] Appl. No.: 273,032

Related US. Application Data [63] Continuation-in-part of Ser. No. 132,508, April 8,

1971, Pat. No. 3,697,812.

[30] Foreign Application Priority Data July 26, 1971 Germany 2137285 [52] US. Cl. 219/501, 317/33 SC [51] Int. Cl. 1105b 1/02 [58] Field of Search 219/501, 469-471;

317/33 SC, 40 A, 40 R; 307/92, 94, 310; 337/182, 102, 103, 153; 338/252, 270;

1,966,466 7/1934 Smalley 337/182 2,425,032 8/1947 Deyrup 338/270 UX 3,383,496 5/1968 Ginsburg 219/501 3,581,062 5/1971 Aston 219/501 3,616,533 11/1971 Heap et a1 174/52 PE 3,697,812 10/1972 Hehl 219/501 Primary Examiner-B. A. Gilheany Assistant Examiner-1 E. Bell Attorney, Agent, or FirmSpencer & Kaye {57] ABSTRACT 174 52 as a coil which concentrically encloses the heatable switching element and an electrically insulating sup- 5 References Cited porting sleeve which supports the coil and is disposed UNITED STATES PATENTS coaxial to the heatable switching element.

1,279,020 9/1918 Schweitzer 337/182 8 Claims, 7 Drawing Figures Mp O PATENTEDFEBZBW Y 3,794,831 1 SHEU 1 UF 2 Fig. 7

PATENTEDFEBZBIBN I 3,794,811

SHEEI 2 0F 2 RELAY CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of applicants copending U.S. Patent Application Ser. No. 132,508, filed on Apr. 8th, 1971 now U.S. Pat. No. 3,697,812, issued on Oct. th, 1972.

BACKGROUND OF THE INVENTION The present invention relates to an improvement in the automatic safety switch disclosed in my above mentioned U.S. Patent Application.

The prior application relates to an automatic safety switch for monitoring the power switching member of an electric current load, such as, for example, an electric heater, an electric motor, or the like, in order to prevent damage which might occur from a malfunction of the power switching member controlling the main current circuit during cutoff. The safety switch contains a relay serving as an auxiliary switching member which is electrically or mechanically connected with the power switching member, an electrical connection between the main current line leading to the electric load and, in one embodiment, an opening contact of the relay, or in another embodiment, an opening contact of the relay which is in turn connected to the power switching member, and a device which is electrically connected with the opening contact and which includes at least one resistance heating element and a heatable switching element in thermal contact with the heating element for disconnectng the load from the main current circuit when a certain temperature is exceeded.

In the prior application the heatable switching element is usually provided in the form of a fuse body and is flanked by two diametrically disposed resistance heating elements. With such a design it mayhappen, particularly upon the occurrence of malfunctions that the resistance heating element comes into electrical contact with the switching element, so that the resistance circuit is connected to the main or operating current circuit. Such a short-circuit generally results in destruction of the amplifier of the safety circuit and damage to the circuit board on which the resisance heating element and the switching element are disposed. In order to overome this danger it has become the practice to additionally insulate the switching element, i.e., the fuse body, with a coating layer of plastic. Such an additional insulation has the drawback, however, that the limit temperature at which electrical cutoff of the load occurs can no longer be reproduced as accurately as when no insulation is used.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to improve the safety circuit discribed above in such a manner that a short-circuit of the heatable switching element is effectively eliminated and the predetermined limit temperature at which safety switch cutoff occurs can be accurately reproduced.

This as well as other objects are accomplished according to the present invention by forming the resistance heating element as a coil of resistance wire which concentrically surrounds the switching element and by providing a supporting sleeve which is disposed coaxial with the switching element.

Advisably the switching element is a radially symmetrical fuse body having at least a central cylindrical section. The body is fully enclosed by the cylindrical inner wall of the supporting sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-sectional view of a resistance heating element according to the present invention.

FIG. 2 is a front view of the heating element of FIG. 1.

FIG. 3 is a longitudinal, partially cross-sectional view of the resistance heating element of FIG. I mounted on a circuit board in combination with terminal columns for a fuse body to be inserted within the heating element.

FIG. 4 is a front view of the mounted heating element of FIG. 3 without the connecting columns.

FIG. 5 is a top plan view, partially in longitudinal section, of the arrangement according to FIGS. 3 and 4 and including a fuse body connected to the terminal columns.

FIG. 6 is a schematic top plan layout of a safety circuit utilizing the element according to the present invention and having an electronic power switching member.

FIG. 7 is a schematic circuit diagram of the safety circuit of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit illustrated in FIGS. 6 and 7 will be first described to permit a better understanding of the purpose, and importance, of the improved switching arrangement according to the invention.

In the circuit, a load 9 is held at a predetermined rated temperature by an electronic temperature control device. The temperature regulating device has a suitable amplifier 8 which moniters the rated temperature at the heated load 9. The amplifier 8 controls an auxiliary relay 7 which together with the amplifier 8 forms an amplifier current circuit. Depending on whether the rated temperature at the heated load 9 has been exceeded or not, the relay 7 with the aid of its switch contact 12 switches a power switching member 6 on or off. The power switching member 6 controls a main current circuit 11 which is provided with a suitable fuse 1. The power switching member 6 may be an electronic power switching member, such as a thyristor. The power switching member 6 which is controlled by the relay 7 via a suitable resistor 5, is disposed directly in the main current circuit 11.

One significant component of the safety circuit is an electrical connection 14 which is situated between the main current circuit 11 and the opening contact 12 of the relay 7. Another significant component is a device 2, 3, 21, 29, 25, 90, which is disposed in the main current circuit 1 l and is electrically connected with the opening contact 12 of the relay 7 via a line 15. The device includes a resistance heating element 3, 21 and a heatable switching element or radially symmetrical fuse body 2 which is in thermal contact with the resistance heating element 3, 21 and which operates, for example, on a chemical basis to become nonconductive upon being heated to a certain temperature.

As can be seen in FIGS, 1-5, the resistance heating element 3, 21 is formed by an electrically insulating 18" extending outwardly from the cylindrical section, V

and operates on a chemical basis as a fuse body. The fuse body is enclosed by the cylindrical inner wall of the supporting sleeve 21. The sleeve is formed preferably of a ceramic body and is disposed coaxially to the radially symmetrical switching element 2. The supporting sleeve 21 is provided with a recess in its outer surface. The coil 3 is formed by a single winding and is disposed in the recess in the supporting sleeve.

A ceramic protective sleeve 29 is connected with a printed circuit type circuit board 27 by means of slide fittings 25. The circuit board 27 carries part of the current circuit of the resistance heating element 3, 21 as well as of the main or operating current circuit 11. The protective sleeve 2? concentrically mounts the assembled switching element 2 and the supporting sleeve 21 'via the fittings 25 to the circuit board 27. The fittings 25 are secured to the circuit board 27. The fittings 25 are secured to the circuit board 27 by rivet-like portions including a stem 25' and a head 26.

Axial grooves are formed in the supporting sleeve 21. The input section 3 and the output section 3", respectively, of the coil 3 pass through the grooves 20 and are electrically and mechanically connected with the circuit board 27 by means of the fittings 25.

A pair of terminal columns 90 and 100 are mounted to the circuit board 27 in a manner similar to the fittings 25. The one terminal 100 is disposed in a plane A-A, which intersects the axis of the fuse body 2. The other terminal 90 is disposed outside of this plane in order to facilitate mounting or dismounting of the fuse body in the supporting sleeve 21. The terminals 18, 18" are received within the columns 100, 90, respectively, and are retained therein by clamping connections 111, 112 in each column. As a result of the mounting of the terminals 18', 18 to the columns 100, 90, the fuse body 2 is electrically connected to the circuit board 27.

Referring again to FIG. 7, if the power switching member 6 becomes conductive due to a defect, for example, and the auxiliary relay 7 remains disconnected, as shown in FIG. 7, one phase, Mp, of the main current circuit 11 is connected to the resistance heating element 3, 21 via the line 14, the opening contact 12, of the relay 7 and the line 15. The resistance heating element 3, 21 heats the switching element 2 until it exceeds a predetermined limit temperature. As a result, the main current circuit 11 is cut off and thus the current flow for the electric load 9 is interrupted. The placement of the resistance heating wire 3 concentric with the fuse body 2 offers absolute protection against a short circuit. Furthermore the fuse body 2 no longer needs to be soldered.

The fuse body 2 is constituted by a thermolabile substance disposed in the conductive path. The fuse body is well-known and can be obtained on the market.

It will be understood that the above description of the present invention is susceptible to various modfications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

.1. A circuit arrangementfor supplying current to an electric power load, as for example, an electric heater, an electric motor and the like, said circuit arrangement comprising, in combination:

a main current circuit having said load and a power switching means for controlling the current to said.

load connected in series;

a first means for'controlling the opening and closing of said power switching means; and

an automatic safety circuit means for monitoring said power switching means controlling said main current circuit to prevent damage to said load which might occur as a result of a malfunction of said power switching member causing it to remain closed when the main current to the load is to be cut off said automatic safety circuit means includ rent to said load out off, to cause said second means to disrupt said main current circuit in the event said power switching means has not opened, said second means including a heatable switching element, an electrical resistance heating element formed as a coil which encloses said heatable switching element, and an electrically insulating supporting sleeve which supports said coil and is disposed around said heatable switching element.

2. The circuit arrangement as defined'in claim 1, wherein said supporting sleeve is formed as a ceramic body having a cylindrical inner wall, and said heatable switching element is a radially symmetrical fuse body having at least a central cylindrical section, the fuse body being enclosed by said cylindrical inner wall.

3. The circuit arrangement as defined in claim 1,

wherein said supporting sleeve has an outer surface with a recess therein, and said coil is formed by a single winding and is disposed in said recess.

4. The circuit arrangement as defined in claim 1, further comprising a circuit board carrying a printed circuit, a protective sleeve which encloses said supporting sleeve, and means for fitting said protective sleeve to said circuit board, said circuit board being a component of the current circuit of said resistance heatingelement and the main current circuit.

5. The circuit arrangement as defined in claim 4, further comprising terminal columns and means for connecting said columns to said circuit board so that said columns serve as electrical conductors, and clamping means, wherein said heatable switching element is a radially symmetrical fuse body having a central cylindrical section and a pair of terminals which are connected to a respective terminal column by said clamping means, said terminals being disposed, when connected to a respective terminal column, in a plane which intersects the axis of the fuse body.

6 6. The circuit arrangement as defined in claim 4, output portion, respectively, of said coil. wherein said coil has an input and output portion, and 8. The circuit arrangement as defined in claim 1, said supporting sleeve has axial grooves therein which wherein said switching element is of a material whose receive said input and output portion, respectively. electrical characteristics charge when said element is 7. The circuit arrangement as defined in claim 6, 5 heated beyond a predetermined temperature so as to wherein said fitting means enclose said protective cause the main current circuit to open. sleeve and include means for receiving said input and l UNITED STATES PATENT OFFICE CERTIFICATE v()F CORRECTION Karl Hehl Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 4, "charge" should read change Signed and sealed this 28th day of January 1975.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE: 930

FORM PO-\ 050 (10-69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3-794.8ll Dated Februarv 26th, 1974 Inventor(s) Karl Hehl It is certified the 1t error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, line 5, change "Oct. 1'' to -October lO-.. Column 3, lines 64 and 65, change "modifications" to -modifi cations-. Column 4, line l7, after "off" insert a comma Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN At'testing Officer Commissionerof Patents FORM PO 105 (10.69) 'USCOMM'DC 60376-P69 UIS. GOVERNMENT PRINTING OFFICE: IQD 0-366-334,

UNITED STATES PATENT OFFICE Karl Hehl Patent No.

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

Column 6, line 4, "charge" should read change Signed and sealed this 28th day of January 1975 (SEAL) Attest:

MCCOY M. GIBSON JR. Attesting Officer C. MARSHALL DANN Commissioner of Patents USCOMM-DC 003764 69 FORM PC4050 (10-69) u.s. covzaunzn'r rnlmrms OFFICE: 930

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3 .794 .811 Dated Februarv 26th, 1974 InVentofls) rl Hehl It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, line 5, change "Oct. 1" to --Octoberl0--. I Column 3, lines 64 and 65, change "modfications" toi--modifications--. Column 4, line l-7, after "off" insert a comma Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents 'USCOMM-DC 60375-P69 F ORM PO- I 050 10-69) U.S4 GOVERNMENT PRINTING OFFICE: I989 0-36S33l.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1279020 *Jan 16, 1914Sep 17, 1918Edmund O SchweitzerFuse device.
US1966466 *Dec 23, 1930Jul 17, 1934Hevi Duty Electric CoElectrically heated electric fuse circuit
US2425032 *Aug 24, 1944Aug 5, 1947Du PontEnamel for resistors
US3383496 *Aug 27, 1965May 14, 1968Leon GinsburgHigh temperature vacuum firing porcelain furnace
US3581062 *Feb 18, 1969May 25, 1971Pavelle CorpElectronic thermostat
US3616533 *Oct 28, 1969Nov 2, 1971North American RockwellMethod of protecting articles in high temperature environment
US3697812 *Apr 8, 1971Oct 10, 1972Hehl KarlAutomatic safety switch for electric current load
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4096370 *Jun 15, 1977Jun 20, 1978Litton Systems, Inc.Microwave oven door interlock switch system
US4222087 *Aug 21, 1978Sep 9, 1980Hawthorne Industries, Inc.Passive triac output asymmetry detector
US4242713 *Oct 25, 1979Dec 30, 1980Goodrich Edward WTriac output asymmetry detector
US5726850 *Jul 24, 1996Mar 10, 1998Rowe, Jr.; William M.Electrical heating apparatus
Classifications
U.S. Classification219/501, 361/104, 361/100
International ClassificationH01H71/12, H01H71/20, H01H61/00, H01H47/00, A61B18/08, H01H61/013, A61B18/04
Cooperative ClassificationH01H61/013, H01H71/20, H01H47/002, A61B18/08
European ClassificationH01H47/00C, H01H71/20, A61B18/08, H01H61/013