Electrical conductor and short circuit locator

Claim 1

An apparatus for locating electrical conductors and short circuits in DC circuits comprising: first and second tests leads for connecting across fuse terminals or the like in a DC circuit to be tested wherein the fuse is blown by a short circuit or removed; current limiting means for limiting the DC current in a circuit being tested to a predetermined value to prevent excessive current in a circuit having a short circuit; the predetermined value being sufficiently high such that the DC current when transformed into pulses is discernable at conducting points in the circuit by a clamp-on ammeter; pulse generating means, connected in series with the current limiting means between the first and second test leads, for intermittently interrupting DC current in the circuit being tested; the frequency and amplitude of the pulses being in the range from 140 to 1400 cycles per second so that a substantially steady current reading is visible on a clamp-on ammeter at all points along the circuit except at the short circuit; the pulse generating means comprising: solid state switching means connected in series with the current limiting means between the first and second test leads for periodically interrupting the DC current in the circuit being tested; and an adjustable frequency oscillator means connected to the solid state switching means to control the switching rate of the solid state switching means; the adjustable frequency oscillator being an astable multivibrator and the solid state switching means being polarity-insensitive and comprising: a first transistor and a first diode, the first diode being connected in series with the collector-emitter circuit of the first transistor to provide a first polarity conduction path; and a second transistor and a second diode, the second diode being connected in series with the collector-emitter circuit of the second transistor to provide a second polarity conduction path; the first transistor and first diode being connected in parallel with the second transistor and second diode; the base of the first and second transistors being connected to the output of the astable multivibrator.

Claim 2

An apparatus for locating electrical conductors and short circuits in DC circuits comprising: first and second tests leads for connecting across fuse terminals or the like in a DC circuit to be tested wherein the fuse is blown by a short circuit or removed; current limiting means for limiting the DC current in a circuit being tested to a predetermined value to prevent excessive current in a circuit having a short circuit; the predetermined value being sufficiently high such that the DC current when transformed into pulses is discernable at conducting points in the circuit by a clamp-on ammeter; pulse generating means, connected in series with the current limiting means between the first and second test leads, for intermittently interrupting DC current in the circuit being tested; the frequency and amplitude of the pulses being in the range from 140 to 1400 cycles per second so that a substantially steady current reading is visible on a clamp-on ammeter at all points along the circuit except at the short circuit; the pulse generating means comprising: solid state switching means connected in series with the current limiting means between the first and second test leads for periodically interrupting the DC current in the circuit being tested; and an adjustable frequency oscillator means connected to the solid state switching means to control the switching rate of the solid state switching means; the adjustable frequency oscillator being an astable multivibrator and the solid state switching means being polarity-insensitive and comprising: a first transistor and a first diode, the first diode being connected in series with the collector-emitter circuit of the first transistor to provide a first polarity conduction path; and a second transistor and a second diode, the second diode being connected in series with the collector-emitter circuit of the second transistor to provide a second polarity conduction path; the first transistor and first diode being connected in parallel with the second transistor and second diode; the base of the first and second transistors being connected to the output of the astable multivibrator.

Claim 3

An apparatus for locating electrical conductors and short circuits in AC circuits, in purely DC circuits, and in DC circuits wherein AC circuits are in a common conductor bundle with the DC circuits, comprising: first and second test leads for connecting across open circuit breaker means in a circuit to be tested wherein the circuit breaker means is open; first current limiting means for limiting AC current in an AC circuit being tested to a predetermined value to prevent excessive short circuit current in the circuit being tested; the predetermined value being sufficiently high such that the AC current is discernable at conducting points in the circuit by a clamp-on ammeter; first pulse generating means, connected in series with the first current limiting means between the first and second test leads, for intermittently interrupting the AC current in the circuit being tested; the first pulse generating means providing an on-duration sufficient for a clamp-on ammeter to indicate a momentary pulse, with the off-duration substantially greater than the on-duration; second current limiting means for limiting the DC current in a DC circuit being tested to a predetermined value to prevent excessive current by short circuit; the predetermined value being sufficiently high such that the DC current when transformed into pulses is discernable at conducting points in the circuit by a clamp-on ammeter; second pulse generating means, connected in series with the first and second current limiting means between the first and second test leads, for intermittently interrupting the DC current in the circuit being tested; the frequency and amplitude of the pulses being sufficient so that a substantially steady current reading is visible on a clamp-on ammeter at all points along the circuit except at the short circuit; switch means for selectively connecting the first and second test leads to the series connection of the first current limiting means and the first pulse generating means for testing circuits, and the series connection of the second current limiting means and the second pulse generating means for testing DC circuits; and superimposing means for selectively placing the first pulse generating means in series with the second pulse generating means while testing a DC circuit in a common conductor bundle with AC circuits; whereby periodic pulses and a steady current reading are observable by a clamp-on ammeter at all points along the circuit except at the short circuit, distinguishing the DC circuit tested from steady current readings observable from adjacent AC conductors.

Claim 4

An apparatus for locating electrical conductors and short circuits in AC circuits, in purely DC circuits, and in DC circuits wherein AC circuits are in a common conductor bundle with the DC circuits, comprising: first and second test leads for connecting across open circuit breaker means in a circuit to be tested wherein the circuit breaker means is open; first current limiting means for limiting AC current in an AC circuit being tested to a predetermined value to prevent excessive short circuit current in the circuit being tested; the predetermined value being sufficiently high such that the AC current is discernable at conducting points in the circuit by a clamp-on ammeter; first pulse generating means, connected in series with the first current limiting means between the first and second test leads, for intermittently interrupting the AC current in the circuit being tested; the first pulse generating means providing an on-duration sufficient for a clamp-on ammeter to indicate a momentary pulse, with the off-duration substantially greater than the on-duration; second current limiting means for limiting the DC current in a DC circuit being tested to a predetermined value to prevent excessive current by short circuit; the predetermined value being sufficiently high such that the DC current when transformed into pulses is discernable at conducting points in the circuit by a clamp-on ammeter; second pulse generating means, connected in series with the first and second current limiting means between the first and second test leads, for intermittently interrupting the DC current in the circuit being tested; the frequency and amplitude of the pulses being sufficient so that a substantially steady current reading is visible on a clamp-on ammeter at all points along the circuit except at the short circuit; switch means for selectively connecting the first and second test leads to the series connection of the first current limiting means and the first pulse generating means for testing circuits, and the series connection of the second current limiting means and the second pulse generating means for testing DC circuits; and superimposing means for selectively placing the first pulse generating means in series with the second pulse generating means while testing a DC circuit in a common conductor bundle with AC circuits; whereby periodic pulses and a steady current reading are observable by a clamp-on ammeter at all points along the circuit except at the short circuit, distinguishing the DC circuit tested from steady current readings observable from adjacent AC conductors.