Typical Directional Detector
f) The test set consists of an amplifier unit; sheath pickup coil; surface pickup coil;
and earth gradient probe frame.
(1) Amplifier Unit. The amplifier unit contains the electronics, the battery, the
output meter, and the controls.
(2) Sheath Pickup Coil. This unit is a C-shaped iron core and coil molded into a
solid rubber assembly. It is designed for optimum pickup of the small, high-frequency magnetic
field surrounding a cable and sheath and has the ability to accurately pick out the one of three
conductors inside the sheath which is carrying the test impulse current.
(3) Surface Pickup Coil. This is a ferrite rod antenna enclosed in a protective tube.
It is held in a T-bracket at the end of a telescoping aluminum rod with rubber handle grip. This
pickup is designed specifically for detecting the magnitude and direction of impulse current
magnetic fields. The T-joint is hinged and detented for positioning at 0 degrees, 45 degrees, and
90 degrees to permit easy location of maximum and minimum signals and, thus, location of the
(4) Earth Gradient Probe Frame. This is a rigid tubular frame supporting two
stainless steel probes at a fixed separation of 20 inches (50 cm) which provides a means of
detecting voltage differential along the surface of the earth. Each probe is wired through a
connecting cord to a plug. The frame is insulated for operator safety.
a) The impulse generator used with this directional detector and the cables to which it
is connected may be a source of high-voltage electrical energy, and all safety precautions listed
in par. 4.7 regarding impulse generators, should be followed. When the directional detector is
used with the earth gradient probes, care must be exercised to avoid contact with any energized
equipment or cables, whether on the surface or buried or whether energized by the impulse
generator or the power line.
b) A hazardous voltage may occur at any of the following locations: