US3666993A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Static hazard detector for isolated alternating current supply lines
Assignee: Electromagnetic Industries Inc
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Filing: 1971-05-13
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Granted: 1972-05-30
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Expires: 1991-05-13
Abstract
Abstract First and second resistors are connected in series with respective capacitors at first and second junction points. The two R-C series combinations are connected between the two line conductors of an isolated AC supply line, with each capacitor being connected to a different line conductor. Each junction point is connected to one terminal of a respective full wave rectifier, and the opposite terminals of the two full wave rectifiers are connected to a third junction point. Current flow through each rectifier is controlled by a respective transistor, and the transistors are alternately triggered conductive by an oscillator. A photoelectric resistor, such as a cadmium sulphide resistor, is connected in series between the third junction point and one terminal of a third full wave rectifier having an AC potential supply thereto so as to serve as an interposed source of DC potential. A lamp subjected to the voltage of the supply line is operatively associated with the photoelectric resistor so that the impedance of the detector circuit, or the ''''source impedance,'''' is varied so that the detector current is maintained at a constant value over the entire voltage range of from 102v to 132v, for a nominal 120v AC supply. The other terminal of the DC source is connected to one terminal of a milliammeter whose opposite terminal is grounded, and diode means are connected to the millianmeter so that fault current can flow therethrough in only one direction. The milliammeter, through the mentioned circuitry, is connected alternately to the first and second junction points for flow of fault current alternately from the line conductors in only one direction to ground through the milliammeter. A switching relay controls signal lights and an alarm, and normally maintains a ''''safe'''' lamp illuminated. Upon occurrence of a fault current flow through the milliammeter, an amplifier amplifies the fault current to energize the relay to switch connections to sound an alarm, to illuminate a ''''hazard'''' lamp, or to do both. Phase shift adjustment means are associated with the R-C series combinations, and a diode is connected in by-pass relation with the third full wave rectifier to direct reverse current flow in by-pass relation to the third full wave rectifier.
Inventors
- 👤 Raymond H Legatti
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 22:13
CPC Classifications
H; H02; H02H; H02H3/00; H02H3/02; H02H3/04; H02H3/16
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
294 words
For use with an AC supply line, having its line conductors isolated from ground and subject to probable connection to ground by any configuration of resistive and capacitive fault impedances, a fault detector circuit arranged for connection to said supply line anD equally sensitive to balanced and unbalanced such fault configurations, said fault detector circuit comprising, in combination, a first capacitor and a first resistor connected in series at a first junction point; a second like capacitor and a second like resistor connected in series at a second junction point; said first capacitor and said second resistor being connected to one line conductor and said second capacitor and said first resistor being connected to the other line conductor, and each resistor having an impedance substantially equal in magnitude to that of one of said capacitors at the supply line frequency; a third junction point; switching and rectifying means operable to effect current flow from said first and second junction points alternately and cyclically to said third junction point; a source of DC potential; a variable impedance connected in series between said third junction point and one terminal of said source, and having an impedance varying directly with the supply line voltage; a milliammeter connected between the other terminal of said source and ground for alternating connection to said first and second junction points to provide a path for current flow alternately from said line conductors in only one direction to ground through said milliammeter; whereby, upon occurrence of any configuration of resistive and capacitive fault impedances, said capacitors and resistors connected between said isolated line conductors will effect a flow of fault current through said milliammeter; and means operatively connected to said milliammeter and blocking current flow through said milliammeter in the reverse direction.
Claim 2
Dependent Claim
294 words
For use with an AC supply line, having its line conductors isolated from ground and subject to probable connection to ground by any configuration of resistive and capacitive fault impedances, a fault detector circuit arranged for connection to said supply line anD equally sensitive to balanced and unbalanced such fault configurations, said fault detector circuit comprising, in combination, a first capacitor and a first resistor connected in series at a first junction point; a second like capacitor and a second like resistor connected in series at a second junction point; said first capacitor and said second resistor being connected to one line conductor and said second capacitor and said first resistor being connected to the other line conductor, and each resistor having an impedance substantially equal in magnitude to that of one of said capacitors at the supply line frequency; a third junction point; switching and rectifying means operable to effect current flow from said first and second junction points alternately and cyclically to said third junction point; a source of DC potential; a variable impedance connected in series between said third junction point and one terminal of said source, and having an impedance varying directly with the supply line voltage; a milliammeter connected between the other terminal of said source and ground for alternating connection to said first and second junction points to provide a path for current flow alternately from said line conductors in only one direction to ground through said milliammeter; whereby, upon occurrence of any configuration of resistive and capacitive fault impedances, said capacitors and resistors connected between said isolated line conductors will effect a flow of fault current through said milliammeter; and means operatively connected to said milliammeter and blocking current flow through said milliammeter in the reverse direction.
Claim 3
Dependent Claim
27 words
A fault detector circuit, as claimed in claim 1, in which at least one of said first and second resistors is adjustable to compensate for phase shift.
Claim 4
Dependent Claim
54 words
A fault detector circuit, as claimed in claim 1, in which said source of DC potential comprises a full wave rectifier bridge having a pair of AC input terminals connected to a source of AC potential; said one terminal and said other terminal of said source comprising the other terminals of said rectifier bridge.
Claim 5
Dependent Claim
43 words
A fault detector circuit, as claimed in claim 3, in which said source of AC potential comprises a transformer having a primary winding connected across said isolated line conductors and a secondary winding connected to said AC input terminals of said rectifier bridge.
Claim 6
Dependent Claim
41 words
A fault detector circuit, as claimed in claim 1, in which said variable impedance comprises a third resistor and a third capacitor connected, in parallel with each other, between said third junction point and said one terminal of said DC source.
Claim 7
Dependent Claim
85 words
A fault detector circuit, as claimed in claim 1, in which said variable impedance comprises a photo-resistor connected between said third junction point and said one terminal of said source, a lamp operable to direct illumination upon said photo-resistor, and means connected to said AC supply line and controlling the illumination of said lamp as an inverse function of the supply line voltage, whereby the resistance of said photo-resistor varies as a direct function of the supply line voltage to maintain the detector current constant.
Claim 8
Dependent Claim
80 words
A fault detector circuit, as claimed in claim 1, in which said switching and rectifying means comprises respective full wave rectifier bridges each having a first terminal connected to a respective one of said first and second junction points and a second terminal connected to said third junction point; respective transistors each having its output circuit connected to the other two points of a respective rectifier bridge; and an oscillator effecting alternate triggering of said transistors to the conductive state.
Claim 9
Dependent Claim
23 words
A fault detector circuit, as claimed in claim 7, in which said oscillator is a transistorized oscillator energized from said AC supply line.
Claim 10
Dependent Claim
69 words
A fault detector circuit, as claimed in claim 3, including a second full wave rectifier bridge having a pair of opposite input terminals cOnnected to said one terminal and said other terminal, respectively, of said first-mentioned rectifier bridge; said milliammeter being connected across the other two terminals of said second full wave rectifier bridge; and means connecting one input terminal of said second full wave rectifier bridge to ground.
Claim 11
Dependent Claim
39 words
A fault detector circuit, as claimed in claim 9, including a diode connected between said one and said other terminal of said first-mentioned full wave rectifier bridge to bypass reverse current flow therearound upon occurrence of a capacitive fault.
Claim 12
Dependent Claim
104 words
A fault detector circuit, as claimed in claim 1, including visual and audible hazard indicating means; relay contacts controlling connection of said indicator means to a source of potential; a relay operating coil controlling said relay contacts; and a transistor amplifier having an input connected to said milliammeter and an output circuit controlling connection of said relay operating coil to a source of potential; said transistor amplifier, responsive to a flow of fault current through said milliammeter, operating said relay operating coil to move said relay contacts to a position connecting said hazard indicator means to a source of potential to energize the same.
Claim 13
Dependent Claim
87 words
A fault detector circuit, as claimed in claim 11, in which said visual hazard indicator means comprises a hazard lamp; said audible hazard indicator means comprising a buzzer; and a ''''safe'''' lamp controlled by said relay contacts; said relay contacts, when said relay operating coil is deenergized, connecting said ''''safe'''' lamp to a source of potential and, upon energization of said relay operating coil, disconnecting said ''''safe'''' indicator lamp from the source of potential and connecting said hazard lamp and said buzzer to a source of potential.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-05-30 | 1975-11-29 | 1976-05-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-05-30 | 1979-11-29 | 1980-05-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-05-30 | 1983-11-29 | 1984-05-30 | $7700.00 | Window Closed / Lapsed |