METHOD OF PRODUCTION TESTING FUSES AND CIRCUIT FOR ACCOMPLISHING SUCH TESTING
First Claim
1. A test circuit for a fuse comprising in combination, an electrical source, means for connecting a fuse across said electrical source, means for providing a test current of preselected magnitude in said fuse, switch means selectively operable to complete the circuit for said fuse and subject said fuse to said test current, and means controlling the operation of said switch means and operating said switch means to complete said circuit for a preselected time, said duration of time and said current magnitude are characterized by being such as to provide a minimum melt i2t for said fuse wherein i is said test current and t is said preselected time.
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Accused Products
Abstract
Quality control testing of production current limiting fuses is achieved by subjecting the fuses to a minimum melt i2t (amp2 seconds) condition. The fuses to be tested are connected in an electrical circuit and subjected to a test current of given magnitude for one loop of a 60 hertz source.
88 Citations
13 Claims
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1. A test circuit for a fuse comprising in combination, an electrical source, means for connecting a fuse across said electrical source, means for providing a test current of preselected magnitude in said fuse, switch means selectively operable to complete the circuit for said fuse and subject said fuse to said test current, and means controlling the operation of said switch means and operating said switch means to complete said circuit for a preselected time, said duration of time and said current magnitude are characterized by being such as to provide a minimum melt i2t for said fuse wherein i is said test current and t is said preselected time.
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2. The test circuit of claim 1 wherein said electrical source is a 60 hertz source, and said switch means is rendered conductive for one loop of said 60 hertz.
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3. The test circuit of claim 2 wherein said switch means is rendered operative upon receipt of a control signal from said control means during one phase of said 60 hertz source, and said control means applies said control signal as said 60 hertz source is changing to said one phase and removes said control signal before said one phase again changes so that said switch means is rendered conductive and said fuse is subjected to said test current for precisely one loop of said 60 hertz.
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4. The test circuit of claim 2 wherein said switch means comprises first electronic switch means characterized by being rendered conductive in response to receipt of a control signal during one phase of said 60 hertz source, said control means includes a second electronic switch means operative to provide said control signal but being out-of-phase with said 60 hertz source to apply said control signal to said first electronic switch Means prior to said 60 hertz source being in said one phase, and said control means further operative to maintain said control signal on said switch means until said 60 hertz source changes to said one phase so that said first electronic switch means is rendered conductive precisely as said 60 hertz source changes to said one phase.
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5. The test circuit of claim 2 wherein said switch means comprises a first SCR connected across said 60 hertz source and in series with said fuse, said SCR being capable of conduction when said 60 hertz source is in one phase, wherein said control means includes a second SCR connected to the gate of said first SCR, including a source of potential connected to and controlled by said second SCR, wherein said control means further includes a control signal generating means connected to said second SCR to selectively turn '"'"''"'"''"'"''"'"'on'"'"''"'"''"'"''"'"' said second SCR and apply the necessary signal to said first SCR to render that SCR conductive, said control signal generating means being out-of-phase with said 60 hertz source to apply said necessary signal prior to said 60 hertz source being in said one phase and maintaining said necessary signal until said 60 hertz source changes to said one phase.
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6. The test circuit of claim 5 wherein said control signal generating means includes a first A.C. source in phase with said 60 hertz source, and means for shifting the phase of said A.C. source 180* relative to said 60 hertz source.
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7. The test circuit of claim 6 wherein said phase shifting means comprises a transformer having its primary connected to said first A.C. source and its secondary connected to the gate of said second SCR.
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8. The test circuit of claim 7 wherein said source of potential comprises a capacitor capable of charging above the trigger voltage of said first SCR and having decay characteristics such that said trigger voltage is held until said 60 hertz source changes to said one phase.
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9. The test circuit of claim 4 wherein said source of potential comprises a capacitor capable of charging above the trigger voltage of said first SCR and having decay characteristics such that said trigger voltage is held until said 60 hertz source changes to said one phase.
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10. The first circuit of claim 9 wherein the decay characteristics of said capacitor are further characterized by said charge thereon decaying below said trigger voltage before said 60 hertz source changes from said one phase.
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11. The method of testing a fuse comprising the steps of providing a preselected magnitude of current, and selectively applying said current to said fuse for a preselected duration of time, wherein said duration of time and said current are selected to provide a value of i2t (i being said current and t being time) equal to the minimum melt i2t for said fuse.
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12. The method of claim 11 wherein said preselected duration of time is a single loop of a 60 hertz electrical source.
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13. A test circuit for a fuse comprising in combination, an A.C. voltage source for said fuse, switch means connected in circuit with said fuse and said voltage source for controlling test current in said fuse and having a non-conductive state and being turned '"'"''"'"''"'"''"'"'on'"'"''"'"''"'"''"'"' in response to a combination of said control signal and the phase of said voltage source, means for providing said control signal to said switch means, and control means for operatively connecting said control signal providing means to said switch means and being 180* out-of-phase operatively with said A.C. voltage source but capable of holding said signal on said switch means through a change in phase of said A.C. voltage source whereby said switch means applies test current to said fuse at the start of the loop of said A.C. voltage source subsequent to that loop in which Said control means is operated.
Specification