Electricity: measuring and testing – Magnetic – Magnetic sensor within material
Patent
1990-10-05
1994-04-12
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Magnetic sensor within material
324226, 324262, G01N 2772, G01N 2782, G01R 3300
Patent
active
053028953
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a detector for detecting discontinuities in a medium to be researched, particularly though not exclusively, for detecting discontinuities inside metal pipes as at joints.
It is desirable to be able to detect joints in gas mains since these can leak. This has become a particular problem since the replacement of manufactured gas by natural gas. The latter is much drier than the former, which can and does lead to joint packings drying out, shrinking and then leaking.
A present proposal for detecting joints in cast iron gas mains is to insert through the main a radio transmitter and to follow the transmitter above ground with a receiver. Reception of a signal indicates a joint.
THE INVENTION
The object of the invention is to provide an improved detector, particularly for detecting joints in gas mains, which alone gives indication of a joint.
According to the invention there is provided a detector for detecting discontinuities in a medium to be researched, the detector comprising: the transmitting coil, whereby magnetic field is set up in the medium with the sonde adjacent it on subjection of the transmitting coil to the said electrical current and the receiving coils have induced in them different voltages if the magnetic coupling from the medium to one of the receiving coils differs from the magnetic coupling from the medium to the other receiving coil due to a discontinuity in the medium; and
It is envisaged that the coils may be arranged parallel with each other, their axes being spaced along the sonde. However in the preferred embodiments, the coils are arranged parallel with each other, their axes being substantially co-axial.
Whilst it is possible for the drive current to be a sinusoidal current, detection is facilitated if the drive current is a series of switched pulses and the receiving coil voltages are compared subsequent to each pulse.
Although it is envisaged that the current generating means together with the comparison means may be provided in a single unit with the coils, in the preferred embodiment the former means are provided remotely from the latter coils in the sonde but connected thereto by a cable. Where the coils are to be used inside a pipeline such as a gas main, the cable is preferably arranged within a flexible rod.
In a particularly advantageous embodiment, for use in sealing gas mains whose joints have been detected as discontinuities, the sonde is provided with sealing compound jetting nozzles, and a connection for a sealing compound supply pipe. Conveniently the sonde has an end spigot at which the flexible rod and the supply pipe are permanently attached and onto which is attached a protection tube, in which the flexible rod and the supply pipe extend.
The flexible rod, supply pipe and protection tube may be accommodated when not in use on a coiling device. The cable may terminate at the hub of the coiling device at slip rings. However it is preferred that it continue as a flexible coil able to tolerate a limited number of twists corresponding to uncoiling of the full length of the flexible rod.
To facilitate pushing along a pipeline, the sonde is a circular cylindrical sonde with rounded ends and having a length appreciably greater--at least twice--than its diameter. This configuration allows the sonde to be pushed along the pipeline whilst resting at the bottom of its curvature and aligned with the length of the pipe.
When the magnetic coupling from the pipeline to both receiving coils is identical, the latter will if identical as preferred provide the same response. Accordingly the comparison means may comprise a voltmeter with the receiving coils wired in series opposition. An audio alarm is preferably arranged to sound at a level of response above a threshold value.
To help understanding of the invention a specific embodiment thereof will now be described with reference to the accompanying drawings.
THE DRAWINGS
FIG. 1 is a diagrammatic perspective view of the sonde of a first embodiment of a detector of t
REFERENCES:
patent: 3361960 (1968-01-01), Renken, Jr. et al.
patent: 3434046 (1969-03-01), Wilson et al.
patent: 4178875 (1979-12-01), Moschetti
patent: 4814702 (1989-05-01), Driggers et al.
British Gas plc
Snow Walter E.
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