Electromagnetic search method and probe assembly for locating underground objects

p0001The invention relates to an electromagnetic search method and a probe assembly for locating below the surface, in particular, in soil or in water, lying objects.

p0002Such search methods are used for the localization of metal objects, particularly in locating deep bombs in the ordnance. Here, the so-called exploratory wellbore is used in particular, in which a probe is lowered into a wellbore on the one hand to avoid the signal even surface contamination and on the other to increase the detection range of the detectors. Even a small noise level can prevent the discovery of a deep bomb. The soil formation plays an important role in determining the depth of the objects sought.

p0003A distinction is made between active and passive search methods in the borehole probe. The active or electromagnetic methods have been used only sporadically in the past, because the detection range of the active processes which operate with electromagnetic alternating fields, are relatively small and have not led to satisfactory results.

p0004Because of the wider reach almost exclusively passive or magnetic methods were previously in the downhole probing for use. The difference in field strength meter used therein are designed such that they detect disturbances in the earth's magnetic field by a differential measurement. In principle, the search arrangement of two magnetic sensitive, spatially accurate aligned inductors which are connected against each other in a kind of bridge. On a homogeneous field distribution the search arrangement compensates for the earth's magnetic field so that the probe can be moved without significant display in the room. Enters in the vicinity of this arrangement, a magnetic object, not only the intensity of the magnetic disturbance, but also their field direction appears. The disadvantage is that any disturbance in the earth's magnetic field, magnetic soils and stones, iron constructions and other disturbance phenomena make it difficult to find in this passive magnetic method, however. Even more information can be difficult to detect by this method.

p0005The invention is therefore the <b>task</b> seeks to provide a method and a probe assembly for locating subsurface objects with which or with which the objects can be located very precisely and accurately determine the depth of objects is possible.

p0006This object is done procedurally with the features of claim 1 and device standpoint with the features of claim 6. Advantageous developments are described in the dependent claims.

p0007According to an essential idea of ​​the invention a large transmitting loop is provided stationary in the search area.

p0008Via the transmitting loop, a pulsed magnetic field is transmitted, which causes the detection objects capable to emit secondary signals. The secondary signals are detected with a probe having at least two foreseen from each other at a defined distance receive windings, wherein the probe is in the range of the transmitting loop is used and the data received from the receive windings secondary signals are supplied to an evaluation unit for determining the object depth.

p0009The probe is preferably moved vertically and thereby lowered into a well. However, there is also the possibility of using the search arrangement for locating superficial lying metal objects, such as ammunition and to the probe to move horizontally in the transmitting loop. The borehole axis is preferably located at the center of the stationary transmitting loop which is preferably designed circular or square, but can also be applied in which a modified form. The loop diameter of the transmitting loop is by a multiple, at least a factor of 10 greater than the borehole diameter.

p0010The invention can be used in the same way on the seabed or on the water surface to locate, for example, floating mines and to determine in what depth they are located. For this purpose a large transmitting loop, for example, as a solid frame, carried by a ship, and the probe is lowered on a cable or a rod into the water. A fixed connection such as a rod is preferably used at flow or measurement during the voyage of the ship.

p0011When the probe is moved vertically to the transmitting loop, so it is preferable to one another to form two receiving loops with a defined distance directly to the reception of the emitted magnetic field and calculate from the different degrees received signals at a defined constant distance of the receiving loops, the distance of the probe to the transmission loop , In this way, the information acquisition can be separated into two parts. First, the depth of the probe is measured, and thus the depth of the object determined by the probe height is determined at the point at which the object signal has its maximum intensity in each case. In addition to the intensity of the object signal also whose direction and shape is evaluated to determine further information about the location, type and shape of the object.

p0012In the reception coils typically a current or voltage signal is measured. In a preferred embodiment the receiving coils are designed as resonant circuits, so that the drop of the induced vibrations can be measured. The excited by the secondary signal sinusoidal voltages fall off by an exponential function. In this way, a more accurate distance measurement can be performed. This method can be applied both for the windings to the depth measurement of the probe as well as for the coils for measuring the radiation emitted from the object secondary radiation. Both measurements can be also carried out alternately in a preferred embodiment of the invention by the same coils.

p0013In another preferred embodiment, the individual receiving channels are sampled at predetermined times and the sampled signals are processed by a circuitry link further. This allows the evaluable intensity of each signal will be greatly increased. Also, a further evaluation of the signal information for specifying object is achieved by such scanning of the individual signals.

p0014Similarly, it is possible to scan and process the signals of the different receiving channels by a circuitry link further also the totality of all receiving channels. From this link the various reception channels can be particular about location and place of the detected object derived, as the different signals are caused by the different spatial position of the various receiver coils. When evaluating the different signals both addition, and subtraction of individual channels or other mathematical operations are conceivable.

p0015The probe assembly comprises according to the invention on a large stationary transmitting loop for transmitting pulsed magnetic fields, a probe with a magnetic measuring core and at least two receiving windings, the receiving coils is from one another at a defined distance and are connected to each of the receiving windings, a receiving channel and a common evaluation unit.

p0016Preferably, however, a plurality of receiving coils on the measuring core is disposed. Of these two reception windings are either additionally or exclusively designed for receiving the directly emitted by the transmitting loop magnetic fields. These are preferably the coils at the upper and lower end of the probe, as these have a maximum, defined distance, thus enabling a particularly exact depth determination of the probe.

p0017In another preferred embodiment, the receiving coils are designed as resonant circuits with a capacitor and an inductor to increase the accuracy of measurement on.

p0018The probe comprises in a further preferred embodiment of an internal pulse transmitter which emits at least two windings one for fine exploratory highly-focused magnetic field. This is especially advantageous in cases where must be sought in the immediate vicinity of large metal masses. This interference effect is determined by the timing differences of the received pulse signals and then eliminated.

p0019The receive channels are advantageously provided with a sample and hold circuit and connected to a microprocessor in order to investigate the individual signals may detail.

p0020The probe is advantageously constructed cylindrical and suitable for receiving the electronics. In the probe, the processing of the measured data takes place. The probe is preferably connected to a cable with an external electronic unit. This cable supplies power and data transfer. However, the data can be sparked or via a wireless radio connection to external electronic unit. These can be worn by the operator and is used for storage and further processing of data for visualization on a screen. In another embodiment of the invention a telemetric positioning system to identify and display the object location is provided in relation to the transmitting loop. Thus, the presentation and classification of measured data on the computer screen is simplified.

p0021The invention of an exemplary embodiment illustrated in the schematic drawing is described in detail. In detail, the schematic representations in:<dl id="dl0001"><dt>Fig. 1</dt><dd>a transmission loop and the lowered into a borehole probe; and</dd><dt>FIG. 2</dt><dd>a probe used on the surface.</dd></dl>

p0022In Figure 1, a large, laid on the ground, stationary transmitting loop 1 is shown, which is operated by a pulse transmitter. 2 The transmitting loop 1 has square or circular shape and a larger at least by a factor of 10 in diameter than the borehole. The pulse transmitter 2 sends at predetermined time intervals current pulses through the transmission loop 1, whereby the current changes in a step function, and generates an extensive magnetic field, which moves up to the predetermined time intervals and degrades. The transmitting loop 1 is designed such that the bore hole 3 is located in the center of the transmitting loop, so as to achieve maximum intensities. Get detection enabled objects, especially metallic objects, so be induced into the effective range of the pulsed magnetic field eddy currents therein, leading to a secondary field. This secondary field is received by the receiving windings 5 ​​of the probe 4 as a locating signal, stored and analyzed in a microprocessor. 6 The top receiving coil 5a and the lowermost receiving winding 5b are designed for direct reception of light emitted from the transmitting loop 1 primary signal. The receiving coils 5a and 5b are connected to a separate receiver system and amplifiers, which receive the relative induction values, caused by the removal of the probe 4 for transmitting loop 1. A second microprocessor 7 has the task to calculate from the varying degrees of amplitude values ​​is distance. An internal pulse transmitter 9 also drives the windings 5a and 5b to emit highly-focused magnetic field to fine-sounding. Also, by this magnetic field, an object to emit a secondary signal are excited, which in turn received by the receiving windings 5, is amplified in the associated amplifiers 8 and is evaluated by the microprocessor. 6 The coils 5a and 5b may also be connected to the evaluation of the object signals to the microprocessor. 6 All the electronics shown in the lower area of ​​the drawing is suitably placed in the probe 4 and the results of the microprocessors 6 and 7 are led via a cable 10 to the external electronics unit 11 of the operator. Of the microprocessors 6 and 7 (MP1 and MP2) calculated results are symbolized by the circles A and B and passed over the cable 10 or via a radio link to the electronic unit 11 of the operator.

p0023In Figure 2 it is shown that the search device can be used with the probe 4 for locating superficial underlying objects. Here, too, it is possible to send to the transmitting loop 1, with the pulse transmitter 2 or the internal pulse generator 9 within the probe 4th The probe 4 is attached via a hinge to a supporting rod 12 so that it is always oriented perpendicular to the ground. The depth is determined in this case by evaluating the secondary signal is received varying degrees to the differently positioned receive windings.