Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Patent
1991-01-23
1993-01-26
Snow, Walter E.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
175 45, G01V 3165, E21B 704
Patent
active
051825163
DESCRIPTION:
BRIEF SUMMARY
The invention relates to moling systems, particularly though not exclusively systems applicable to the installation of gas pipes or other services in the ground.
The moling system to which this invention relates is one in which the angular position of the mole about its longitudinal axis is required to be known.
Such angular position of the mole is referred to the "roll angle". The mole is, for example, a percussive mole attached to the leading end of a series of hollow, drill rods through which air is supplied to the percussive mechanism of the mole. The mole has a head at its leading end incorporating a slant face. The mole head receives a transverse steering force at its slant face as it is advanced. To bore approximately in a straight line the drill rods and the mole are rotated at approximately 20 revolutions per minute so that the mole pursues a corkscrew path. To steer, rotation is stopped to leave the slant face in the required orientation. Air continues to be fed to the mole which advances along the curved path dictated by the steering force experienced by the slant face.
The object of the invention is to provide a moling system in which the roll angle of the mole is determined using a radio sonde located in the mole.
According to the invention, a moling system which is capable of giving an indication of mole location and depth comprises a rotatable mole, a radio sonde in the mole having a first transmit coil lying parallel to the lengthwise direction of the mole and a second transmit coil lying transverse to said direction, means including a battery and an oscillator for energising the transmit coils with alternating current with a phase difference between the coils and a receiver traversable above ground into a position in which it can give an indication of roll angle.
In one form of system the radio sonde has a first transmit coil lying parallel to the lengthwise direction of the mole and a second transmit coil lying transverse to said direction, the coils being energised by a single frequency, the energising voltages to the two coils having a phase difference between them and the radiated field from the coils being used for location and measurement of roll angle and depth.
In another form of system the radio sonde has a first transmit coil lying parallel to the lengthwise direction of the mole and a second transmit coil lying transverse to said direction, the coils are energised by a single frequency, the energising voltages to the two coils having a phase difference between them and the radiated field from the coils being used for roll angle measurement only, and the coil lying parallel to the lengthwise direction of the mole being additionally energised with a second frequency and the resulting radiated field being used for location and depth measurement.
In another form of system the radio sonde has a first and a second transmit coil lying parallel to the lengthwise direction of the mole and a third transmit coil lying transverse to said direction, the first transmit coil being energised by a first frequency and the resulting radiated field being used for location and depth measurement, and the second and third transmit coils being energised by a second frequency, the energising voltages to the two coils having a phase difference between them and the resultant radiated field being used for roll angle measurement only.
In one form cf system, the receiver comprises a horizontal phase-reference receive coil and one other receive coil transverse to said phase-reference coil, which receiver is traversable above ground until said phase-reference receive coil is directly above the sonde and parallel to said first transmit coil, the receiver further comprising first means for measuring the variations of the amplitude of the signal from said other receive coil as the mole rotates, a second means for displaying the amplitude variations as an indication of roll angle, and a third means for detecting the phase reversal which occurs in the signal from the transverse receive coil as the mole rotates.
In
REFERENCES:
patent: 3746106 (1973-07-01), McCullough et al.
patent: 4621698 (1986-11-01), Pittard et al.
Glen Stephen J.
Ward Peter
British Gas plc
Snow Walter E.
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