Varistor defect detection by incipient hot spot observation

Claim 1

A method for detecting defects in varistors, comprising the steps of: (a) providing a varistor having first and second opposed major sides and having first and second uninterrupted electrically and thermally conductive electrodes disposed respectively on and substantially completely covering said first and second sides of said varistor, (b) providing only one current pulse through said varistor; (c) mapping a temperature distribution across at least one of said first and second electrodes after said current pulse before temperature variations across said at least one electrode induced by said current pulse can equillibrate; (d) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (e) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said varistor if said mapped temperature distribution includes a temperature at least as high as said treshold temperature.

Claim 2

A method for detecting defects in varistors, comprising the steps of: (a) providing a varistor having first and second opposed major sides and having first and second uninterrupted electrically and thermally conductive electrodes disposed respectively on and substantially completely covering said first and second sides of said varistor, (b) providing only one current pulse through said varistor; (c) mapping a temperature distribution across at least one of said first and second electrodes after said current pulse before temperature variations across said at least one electrode induced by said current pulse can equillibrate; (d) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (e) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said varistor if said mapped temperature distribution includes a temperature at least as high as said treshold temperature.

Claim 10

A method for detecting defects in varistors, comprising the steps of: (a) providing a varistor having first and second uninterrupted electrodes on first and second sides of said varistor, respectively; (b) providing only one current pulse through said varistor through first and second pairs of knife-shaped electrodes arranged orthogonally to each other, respectively pressed against said first and second varistor electrodes; (c) mapping a temperature distribution of at least one of said first and second varistor sides after said current pulse; (d) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (e) comapring said mapped temperature distribution to said threshold level and assigning a defect status to said varistor if a maximum of said temperature distribution is at least as high as said threshold temperature.

Claim 11

A method for detecting defects in varistors, comprising the steps of: (a) providing a varistor having first and second uninterrupted electrodes on first and second sides of said varistor, respectively; (b) providing only one current pulse through said varistor through first and second pairs of knife-shaped electrodes arranged orthogonally to each other, respectively pressed against said first and second varistor electrodes; (c) mapping a temperature distribution of at least one of said first and second varistor sides after said current pulse; (d) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (e) comapring said mapped temperature distribution to said threshold level and assigning a defect status to said varistor if a maximum of said temperature distribution is at least as high as said threshold temperature.

Claim 12

A method for detecting defects in varistors comprising the steps of: (a) providing a varistor having first and second opposed major side and having first and second uninterrupted electrically and thermally conductive electrodes disposed respectively on and substantially completely covering said first and second sides of said varistor; (b) applying a coating of substantially uniform emissivity to an electrode of said varistor; (c) pressing a pair of knife-shaped electric contacts against said first varistor electrode; (d) providing only one current pulse through said varistor; (e) mapping a temperature distribution across said coated electrode after application of said current pulse before temperature variations across said electrode induced by said current pulse can equillibrate; (f) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (g) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said varistor if said mapped temperature distribution includes a temperature at least as high as said threshold temperature.

Claim 13

A method for detecting defects in varistors comprising the steps of: (a) providing a varistor having first and second opposed major side and having first and second uninterrupted electrically and thermally conductive electrodes disposed respectively on and substantially completely covering said first and second sides of said varistor; (b) applying a coating of substantially uniform emissivity to an electrode of said varistor; (c) pressing a pair of knife-shaped electric contacts against said first varistor electrode; (d) providing only one current pulse through said varistor; (e) mapping a temperature distribution across said coated electrode after application of said current pulse before temperature variations across said electrode induced by said current pulse can equillibrate; (f) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (g) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said varistor if said mapped temperature distribution includes a temperature at least as high as said threshold temperature.

Claim 20

A method for detecting defects in varistors comprising the steps of: (a) providing a varistor having first and second opposed major sides and having first and second uninterrupted electrically and thermally conductive electrodes disposed respectively on and substantially completely covering said first and second sides of said varistor; (b) applying a coating of substantially uniform emissivity to said first varistor electrode; (c) pressing a pair of knife-shaped electric contacts against said first varistor electrode; (d) providing only one current pulse through said varistor; (e) mapping a temperature distribution across said first varistor electrode after said current pulse before temperature variations across said electrode induced by said current pulse can equillibrate; (f) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (g) comparing the mapped temperature distribution to said threshold temperature level and assigning a defect status to said varistor if said mapped temperature distribution includes a temperature at least as high as said threshold temperature.

Claim 21

A method for detecting defects in varistors comprising the steps of: (a) providing a varistor having first and second opposed major sides and having first and second uninterrupted electrically and thermally conductive electrodes disposed respectively on and substantially completely covering said first and second sides of said varistor; (b) applying a coating of substantially uniform emissivity to said first varistor electrode; (c) pressing a pair of knife-shaped electric contacts against said first varistor electrode; (d) providing only one current pulse through said varistor; (e) mapping a temperature distribution across said first varistor electrode after said current pulse before temperature variations across said electrode induced by said current pulse can equillibrate; (f) selecting a threshold temperature level for said varistor indicative of the existence of a defect therein; and (g) comparing the mapped temperature distribution to said threshold temperature level and assigning a defect status to said varistor if said mapped temperature distribution includes a temperature at least as high as said threshold temperature.

Claim 22

A method for detecting defects in current conducting devices comprising the steps of: (a) providing a current conducting device having first and second opposed major sides and having a first uninterrupted electrically and thermally conductive electrode on and substantially completely covering a first side thereof and a second electrode on a second side thereof; (b) providing a current pulse through said current conducting device; (c) mapping a temperature distribution across said first electrode after said current pulse before temperature variations across said first electrode induced by said current pulse can equillibrate; (d) selecting a threshold temperature level for said current conducting device indicative of the existence of a defect therein; and (e) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said current conducting device if said mapped temperature distribution includes a temperature at least as high as said threshold temperature.

Claim 23

A method for detecting defects in current conducting devices comprising the steps of: (a) providing a current conducting device having first and second opposed major sides and having a first uninterrupted electrically and thermally conductive electrode on and substantially completely covering a first side thereof and a second electrode on a second side thereof; (b) providing a current pulse through said current conducting device; (c) mapping a temperature distribution across said first electrode after said current pulse before temperature variations across said first electrode induced by said current pulse can equillibrate; (d) selecting a threshold temperature level for said current conducting device indicative of the existence of a defect therein; and (e) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said current conducting device if said mapped temperature distribution includes a temperature at least as high as said threshold temperature.

Claim 29

A method for detecting defects in current conducting devices comprising the steps of: (a) providing a current conducting device having a first uninterrupted electrically and thermally conductive electrode on a first side thereof and a second interrupted electrically and thermally conductive electrode on a second side thereof; (b) providing only one current pulse through said current conducting device with a current level and time duration product at least equal to a current level and time duration product rating of said current conducting device; (c) mapping a temperature distribution of said first electrode after said current pulse before temperature variations across said first electrode induced by said current pulse can equillibrate; (d) providing a visual display apparatus indicia of the mapped temperature distribution; (e) selecting a threshold temperature level for said current conducting device indicative of the existence of a defect therein; and (f) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said current conducting device if said temperature distribution includes a temperature at least as high as said threshold temperature.

Claim 30

A method for detecting defects in current conducting devices comprising the steps of: (a) providing a current conducting device having a first uninterrupted electrically and thermally conductive electrode on a first side thereof and a second interrupted electrically and thermally conductive electrode on a second side thereof; (b) providing only one current pulse through said current conducting device with a current level and time duration product at least equal to a current level and time duration product rating of said current conducting device; (c) mapping a temperature distribution of said first electrode after said current pulse before temperature variations across said first electrode induced by said current pulse can equillibrate; (d) providing a visual display apparatus indicia of the mapped temperature distribution; (e) selecting a threshold temperature level for said current conducting device indicative of the existence of a defect therein; and (f) comparing said mapped temperature distribution to said threshold temperature level and assigning a defect status to said current conducting device if said temperature distribution includes a temperature at least as high as said threshold temperature.