Abstract: An underground pipe and cable locator for continuous depth readings comprises a top and bottom receiver antenna sensor each connected to respective amplifier channels. A separate transmitter is used to stimulate electromagnetic radiations from a buried pipe, cable, or other electrical conductor. The bottom receiver antenna sensor is sampled and used to synchronize a phase locked loop controlled oscillator. The exceedingly faint and noise-riddled signals obtained from the top and bottom receiver antenna sensors are full-wave rectified without the use of rectifiers or diodes that can introduce distortions and offsets. Such signals are full-wave rectified by synchronously switching between inverted and non-inverted copies with an analog switch such that only the positive cycles of each are output in one pulse train. A continuous output is therefore obtainable from the top and bottom receiver antenna sensors, and this, in turn, permits a continuous display of the depth estimate of the buried conductor.

Abstract: A method for locating the joints and fractures of underground cast iron gas mains comprises connecting several sections of an underground cast iron gas main pipeline across a sixty watt signal generator with an audio-frequency signal output of 7800 hertz. The connections take advantage of service lines, valve boxes and drip access at the surface, otherwise holes are drilled to accommodate contact probes. The signal passes through the pipe sections and their joints in series. The centerline of the underground cast iron gas main pipeline is plotted directly above on the surface of the ground, e.g., along a surface centerline. The relatively higher impedance of the pipe joints compared to the pipes themselves, causes current fluxes to radiate from each joint. The relative linear positions and their corresponding signal power measurements are collected along the surface centerline.

Abstract: An apparatus and method for determining the location of a concealed conductive object. The method includes the steps of determining the lateral position of the object by using an antenna array to detect a signal propagating on the object. The antenna array is comprised of at least one center antenna positioned perpendicular to a surface concealing the object and at least two antennas symmetrically positioned about the center antenna at angles not equal to ninety degrees. The depth of the concealed object is determined by using a bottom sensor to detect the signal propagating on the object as a first signal. A vertically displaced top sensor then detects the signal as a second signal which is amplified by a variable gain amplifier until it equals the first signal. The depth of the object is calculated from the gain increase required to achieve equality between the first and second signals.

Abstract: An apparatus to measure the distance to a concealed conductive object, radiating an electromagnetic signal, has two sensors, each adapted to receive the signal and to produce an output voltage proportional to the amount of signal received. Amplifier means amplify the output voltage. Automatic gain control means automatically controls the gain to the amplifier means such that the gain of the amplification of one of the output voltages is the same as the gain of the amplification of the other output voltage. Computing means calculate the distance based upon the two amplified output voltages. Display means display the calculated value.

Abstract: An apparatus to measure the distance to a concealed conductive object, radiating an electromagnetic signal, has two sensors, each adapted to receive the signal and to produce an output voltage proportional to the amount of signal received. Amplifier means amplify the output voltage. Automatic gain control means automatically controls the gain to the amplifier means such that the gain of the amplification of one of the output voltages is the same as the gain of the amplification of the other output voltage. Computing means calculate the distance based upon the two amplified output voltages. Display means display the calculated value.