US3870950A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Overvoltage protected, battery powered electric circuit tester
Assignee: Taco Tafel GmbH and Co KG
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Filing: 1973-12-17
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Granted: 1975-03-11
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Expires: 1993-12-17
Abstract
Abstract To protect an electrical continuity tester, having an internal battery and adapted for connection to distribution power lines, against spurious voltages in the circuit to be tested, a positive temperature coefficient resistor is placed in series with a voltage-controllable semiconductor switch; an acoustic, or visual indicator is placed in series with the battery across the voltage-controllable semiconductor switch. The internal battery is of such value as to be below the triggering value of the semiconductor switch and, preferably, higher than the voltage drop across the semiconductor switch, when in breakdown condition. In case of extraneous voltages on the circuits to be tested, the semiconductor switch will break down, permitting self-limiting current flow through the PTC resistor, and bypassing high voltages from the self-contained battery and indicator.
Inventors
- 👤 Heinz Laass
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 17:48
CPC Classifications
G; G01; G01R; G01R1/00; G01R1/36
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
264 words
External Voltage protected electrical continuity tester to test the continuity of normally deenergized, connected electrical lines but which may have voltages applied thereto, said tester having a pair of input terminals (1, 2); a protective circuit comprising a positive temperature coefficient (PTC) resistor (3) and a voltage-controllable semiconductor switch (5) connected in series to the PTC resistor (3) the free terminal of the PTC resistor, and of the switch (5) being connected to the respective tester input terminals (1, 2); and a continuity checking circuit comprising a voltage source (8) and a current flow indicator (7) connected in series to the voltage source (8), the free terminal of the voltage source, and of the indicator being connected, respectively, across the semiconductor switch (5), the voltage source (8) having an output voltage which is below the breakdown voltage of the semiconductor switch to permit connection of the terminals (1, 2) to deenergized connected lines to be tested for continuity and provide a signal from the current indicator (7) due to current flow through the connected lines and the cold-resistance of the PTC resistor upon detection of continuity while, if the lines should be energized by a voltage normally destructive to the current indicator, the voltage-controlled semiconductor switch (5) will become conductive and permit current to flow through the PTC resistor which will self-limit the current upon heating thereof due to said current flow, the voltage drop across the semiconductor switch during conduction of the switch being less than the voltage which would damage at least one of: said voltage source (8); said current indicator (7).
Claim 2
Dependent Claim
264 words
External Voltage protected electrical continuity tester to test the continuity of normally deenergized, connected electrical lines but which may have voltages applied thereto, said tester having a pair of input terminals (1, 2); a protective circuit comprising a positive temperature coefficient (PTC) resistor (3) and a voltage-controllable semiconductor switch (5) connected in series to the PTC resistor (3) the free terminal of the PTC resistor, and of the switch (5) being connected to the respective tester input terminals (1, 2); and a continuity checking circuit comprising a voltage source (8) and a current flow indicator (7) connected in series to the voltage source (8), the free terminal of the voltage source, and of the indicator being connected, respectively, across the semiconductor switch (5), the voltage source (8) having an output voltage which is below the breakdown voltage of the semiconductor switch to permit connection of the terminals (1, 2) to deenergized connected lines to be tested for continuity and provide a signal from the current indicator (7) due to current flow through the connected lines and the cold-resistance of the PTC resistor upon detection of continuity while, if the lines should be energized by a voltage normally destructive to the current indicator, the voltage-controlled semiconductor switch (5) will become conductive and permit current to flow through the PTC resistor which will self-limit the current upon heating thereof due to said current flow, the voltage drop across the semiconductor switch during conduction of the switch being less than the voltage which would damage at least one of: said voltage source (8); said current indicator (7).
Claim 3
Dependent Claim
264 words
External Voltage protected electrical continuity tester to test the continuity of normally deenergized, connected electrical lines but which may have voltages applied thereto, said tester having a pair of input terminals (1, 2); a protective circuit comprising a positive temperature coefficient (PTC) resistor (3) and a voltage-controllable semiconductor switch (5) connected in series to the PTC resistor (3) the free terminal of the PTC resistor, and of the switch (5) being connected to the respective tester input terminals (1, 2); and a continuity checking circuit comprising a voltage source (8) and a current flow indicator (7) connected in series to the voltage source (8), the free terminal of the voltage source, and of the indicator being connected, respectively, across the semiconductor switch (5), the voltage source (8) having an output voltage which is below the breakdown voltage of the semiconductor switch to permit connection of the terminals (1, 2) to deenergized connected lines to be tested for continuity and provide a signal from the current indicator (7) due to current flow through the connected lines and the coldresistance of the PTC resistor upon detection of continuity while, if the lines should be energized by a voltage normally destructive to the current indicator, the voltage-controlled semiconductor switch (5) will become conductive and permit current to flow through the PTC resistor which will self-limit the current upon heating thereof due to said current flow, the voltage drop across the semiconductor switch during conduction of the switch being less than the voltage which would damage at least one of: said voltage source (8); said current indicator (7).
Claim 4
Dependent Claim
264 words
External Voltage protected electrical continuity tester to test the continuity of normally deenergized, connected electrical lines but which may have voltages applied thereto, said tester having a pair of input terminals (1, 2); a protective circuit comprising a positive temperature coefficient (PTC) resistor (3) and a voltage-controllable semiconductor switch (5) connected in series to the PTC resistor (3) the free terminal of the PTC resistor, and of the switch (5) being connected to the respective tester input terminals (1, 2); and a continuity checking circuit comprising a voltage source (8) and a current flow indicator (7) connected in series to the voltage source (8), the free terminal of the voltage source, and of the indicator being connected, respectively, across the semiconductor switch (5), the voltage source (8) having an output voltage which is below the breakdown voltage of the semiconductor switch to permit connection of the terminals (1, 2) to deenergized connected lines to be tested for continuity and provide a signal from the current indicator (7) due to current flow through the connected lines and the coldresistance of the PTC resistor upon detection of continuity while, if the lines should be energized by a voltage normally destructive to the current indicator, the voltage-controlled semiconductor switch (5) will become conductive and permit current to flow through the PTC resistor which will self-limit the current upon heating thereof due to said current flow, the voltage drop across the semiconductor switch during conduction of the switch being less than the voltage which would damage at least one of: said voltage source (8); said current indicator (7).
Claim 5
Dependent Claim
16 words
Tester according to claim 1, wherein the semiconductor switch is a triac connected to be self-triggering.
Claim 6
Dependent Claim
35 words
Tester according to claim 1, wherein the PTC resistor comprises a metal filament incandescent lamp which, when the tester is connected to an energized circuit, will provide an indication of such energization, by becoming lit.
Claim 7
Dependent Claim
20 words
Tester according to claim 1, wherein the semiconductor switch comprises at least one of: thyristor, triac, transistor, or voltage-controlled diode.
Claim 8
Dependent Claim
31 words
Tester according to claim 1, wherein the semiconductor switch is of the type that its conduction is controlled by a voltage applied thereacross without separate energization from an external control source.
Claim 9
Dependent Claim
11 words
Tester according to claim 1, wherein the semiconductor switch is bi-polar.
References Cited (Backward Citations)
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US3423636A
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US3343085A
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-03-10 | 1978-09-09 | 1979-03-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-03-10 | 1982-09-09 | 1983-03-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-03-10 | 1986-09-09 | 1987-03-11 | $7700.00 | Window Closed / Lapsed |