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Patent US3699308A successfully refreshed from Google Patents.
US3699308A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Electrical heating elements
Assignee: Thermal Syndicate Ltd
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Filing: 1970-10-13
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Granted: 1972-10-17
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Expires: 1990-10-13
Abstract
Abstract A method and apparatus for improving the ''''apparent'''' resistance of an electrical heating element of the type comprising an axial resistance element of the type comprising an axial resistance element insulated from a conducting sheath by a refractory material wherein the refractory material is subjected to an electrolysing D.C. potential applied between the element and the sheath.
Inventors
- 👤 Eric Hutchinson
- 👤 Gordon Hetherington
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 21:58
CPC Classifications
H; H05; H05B; H05B3/00; H05B3/40; H05B3/42; H05B3/48
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
74 words
A method of effecting a significant practical reduction in the overall leakage current with time occurring across a refractory material electrically insulating an axial resistance element from a surrounding electrically conducting sheath in a heating element, comprising the steps of heating said element by applying a A.C. voltage thereacross, periodically applying a unidirectional D.C. potential between the sheath and the resistance element of a magnitude and for a time sufficient to effect said reduction.
Claim 2
Independent Claim
74 words
A method of effecting a significant practical reduction in the overall leakage current with time occurring across a refractory material electrically insulating an axial resistance element from a surrounding electrically conducting sheath in a heating element, comprising the steps of heating said element by applying a A.C. voltage thereacross, periodically applying a unidirectional D.C. potential between the sheath and the resistance element of a magnitude and for a time sufficient to effect said reduction.
Claim 3
Dependent Claim
38 words
A method as claimed in claim 1 wherein in said step of periodically applying a D.C. potential the sheath and the resistance element, the D.C. potential used is between 5 and 20 percent of the A.C. voltage applied.
Claim 4
Dependent Claim
19 words
A method as claimed in claim 1 in said step the D.C. voltage applied is at least 5 volts.
Claim 5
Dependent Claim
48 words
A method as claimed in claim 3, wherein in said step of periodically applying a D.C. potential the ratio of the total period during which the D.C. potential is applied to the total period during which it is not applied lies between the limits 30: 70 and 1:99.
Claim 6
Dependent Claim
16 words
A method as claimed in claim 4 the said ratio in said step is about 5:95.
Claim 7
Dependent Claim
24 words
A method as claimed in claim 4 wherein said step each period during which the D.C. potential is applied is less than 2 minutes.
Claim 8
Dependent Claim
22 words
A method as claimed in claim 6 wherein said step the D.C. potential is applied for a few seconds in each minute.
Claim 9
Dependent Claim
38 words
A method as claimed in claim 1 wherein in said step of periodically applying a D.C. potential between the sheath and the resistance element, the D.C. potential used is above five per cent of the A.C. voltage applied.
Claim 10
Dependent Claim
48 words
A method as claimed in claim 8, wherein in said step of periodically applying a D.C. potential the ratio of the total period during which the D.C. potential is applied to the total period during which it is not applied lies between the limits 30: 70 and 1:99.
Claim 11
Dependent Claim
16 words
A method as claimed in claim 9 the said ratio in said step is about 5:95.
Claim 12
Dependent Claim
24 words
A method as claimed in claim 9 wherein said step each period during which the D.C. potential is applied is less than 2 minutes.
Claim 13
Dependent Claim
22 words
A method as claimed in claim 11 wherein said step the D.C. potential is applied for a few seconds in each minute.
Claim 14
Dependent Claim
92 words
An electric heating apparatus having a heating element with an axial resistance element insulated from a grounded conducting sheath by a layer of a refractory material, a device for increasing the effective resistance of said refractory material comprising means applying an A.C. voltage across the resistance element, second means applying between the sheath and the resistance element a unidirectional D.C. voltage of a magnitude and for a time sufficient to achieve a practical significant increase in the effective resistance of said refractory material, and third means for periodically interrupting said D.C. voltage.
Claim 15
Dependent Claim
92 words
An electric heating apparatus having a heating element with an axial resistance element insulated from a grounded conducting sheath by a layer of a refractory material, a device for increasing the effective resistance of said refractory material comprising means applying an A.C. voltage across the resistance element, second means applying between the sheath and the resistance element a unidirectional D.C. voltage of a magnitude and for a time sufficient to achieve a practical significant increase in the effective resistance of said refractory material, and third means for periodically interrupting said D.C. voltage.
Claim 16
Dependent Claim
35 words
A device as claimed in claim 13, in which the second means comprises a series-connected diode and resistor disposed in parallel with a switch serving to disconnect the A.C. voltage supply from the heating element.
Claim 17
Dependent Claim
20 words
A device as claimed in claim 13, in which the second means is positioned in series with said axial resistance.
Claim 18
Dependent Claim
45 words
A device as claimed in claim 13, in which the second means comprises a thyristor-type device in parallel with a Zener-diode type device plus a capacitor with the control of the thyristor-type device connecting to the junction between the capacitor and the Zener-diode type device.
Claim 19
Dependent Claim
29 words
A device as claimed in claim 13 wherein the D.C. voltage applied by said second means is five per cent above the A.C. voltage applied by the first means.
Claim 20
Dependent Claim
21 words
A device as claimed in claim 13 wherein the D.C. voltage applied by said second means is at least 5 volts.
References Cited (Backward Citations)
US2686250A
Cited
US2921174A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-10-17 | 1976-04-17 | 1976-10-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-10-17 | 1980-04-17 | 1980-10-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-10-17 | 1984-04-17 | 1984-10-17 | $7700.00 | Window Closed / Lapsed |