Abstract This electric field proximity detector enables a worker to detect the presence of a dangerous power line or other electrical source and to then maintain a safe separation from it. A power line need not carry any current as a condition for detection since the device operates on the electric field about the conductor. Response to spurious radiation is eliminated, a sensitivity control is provided to permit setting the device to respond to various fixed combinations of field strength and distance from power lines, a threshold circuit will mark the boundary of safe operation within very narrow limits once the device is adjusted for a particular set of conditions; and a self-testing feature permits the operator to determine the working condition of the device. This miniaturized device contains its own power supply and loudspeaker, making for easy installation on cranes, aerial personnel baskets, and other types of lifting and construction equipment which may be used near power lines. The alarm circuit may also be used to activate other electrical circuits causing machinery to shut down when the alarm is activated. This device may also be used as a test instrument to detect energized lines and sources.
A highly sensitive alarm system for detecting a radiated electrostatic field and for sounding a warning when the alarm system approaches closer than an adjustable preset distance to the source of said field, comprising an audible alarm generator; an electrical threshold gate circuit including signal rectifying and integrating means and means to operate said alarm generator when the integrated signal reaches a predetermined level; an antenna sensitive to an electrostatic field; amplifier means coupling the antenna to said gate circuit to deliver an input signal from the antenna thereto proportional to the intensity of the field; sensitivity adjusting means coupled to the amplifier means for adjusting its gain; a test signal generator separate from the amplifier means and operative when energized to generate a test signal of the same frequency as the electrostatic field to be detected and to couple to said antenna ahead of the sensitivity adjusting means a small component of the test signal of fixed magnitude approximating the magnitude of an input signal resulting from an electrostatic field detectible by said antenna to which the sensitivity adjusting means should be set; and switch means for selectivity energizing said test generator.
Claim 2
Dependent Claim
193 words
A highly sensitive alarm system for detecting a radiated electrostatic field and for sounding a warning when the alarm system approaches closer than an adjustable preset distance to the source of said field, comprising an audible alarm generator; an electrical threshold gate circuit including signal rectifying and integrating means and means to operate said alarm generator when the integrated signal reaches a predetermined level; an antenna sensitive to an electrostatic field; amplifier means coupling the antenna to said gate circuit to deliver an input signal from the antenna thereto proportional to the intensity of the field; sensitivity adjusting means coupled to the amplifier means for adjusting its gain; a test signal generator separate from the amplifier means and operative when energized to generate a test signal of the same frequency as the electrostatic field to be detected and to couple to said antenna ahead of the sensitivity adjusting means a small component of the test signal of fixed magnitude approximating the magnitude of an input signal resulting from an electrostatic field detectible by said antenna to which the sensitivity adjusting means should be set; and switch means for selectivity energizing said test generator.
Claim 3
Dependent Claim
44 words
In an alarm system as set forth in claim 1 and intended for use in detecting the field in the vicinity of a power line energized at a standard power-line frequency, said test generator comprising an oscillator oscillating at said standard frequency when energized.
Claim 4
Dependent Claim
60 words
In an alarm system as set forth in claim 1, a power supply; and a main switch operative when closed to deliver power to said alarm system from said supply, said test generator switch means being coupled to said power supply through said main switch so that the test generator can be energized only when the main switch is closed.