NL2002124C

NL2002124C - Assembly and method for detection of submerged objects.

Info

Publication number: NL2002124C
Application number: NL2002124A
Authority: NL
Inventors: Paulus Benedictus Roest
Original assignee: Groundtracer B V
Priority date: 2008-10-22
Filing date: 2008-10-22
Publication date: 2010-04-23

Description

No. NLP183988A

Assembly and method for detection of submerged objects

BACKGROUND

The invention relates to an assembly and method for detection of submerged objects such as objects located 5 below a ground surface and/or water surface.

SUMMARY OF THE INVENTION

10 According to a first aspect the present invention provides a detection assembly for detecting an object submerged in a covering material, said assembly comprising a mobile electrode movable over a surface of the covering material and adapted to make continuous electrical 15 contact therewith during such movement, a reference electrode contacting the covering material, potential difference (PD) measuring means conductively connected to said electrodes and arranged for measuring a potential difference between the mobile and the reference electrode, 20 and indicator means arranged for indicating a change in measured potential difference during movement of the mobile electrode. Advantageously the mobile electrode can be moved across several patches of area to be investigated while performing measurements. The changes in measured PDs are 25 instantly available and may immediately be used to decide where to dig or survey next, or may be recorded for later processing, for example to build a map of the area under 2 investigation. Contrary to devices using an induced potential, there is no additional risk to an person operating this embodiment of the detection assembly, as the assembly uses very small currents and the PDs between 5 electrodes caused by spontaneous potentials are in the millivolt range (typically between 10 and 100 mV) , which is not even sufficient to penetrate human skin. Indeed, this embodiment may improve safety during digging and surveying operations as the mobile electrode can be used to detect a 10 contour of electrical cables in a much more precise manner, making them easier to avoid.

In an embodiment the reference electrode is arranged to be placed stationary with respect to the covering material and said mobile electrode is movable with 15 respect to the stationary reference electrode. The stationary and mobile electrodes may be connected to the potential difference measuring means using insulated cables of sufficient length to span the distance between the electrodes while still allowing some slack for the cables. 20 This embodiment allows the use of a stationary reference electrode without significantly affecting the mobility of the mobile electrode.

According to a second aspect, the invention provides a detection assembly for detecting an object 25 submerged in a covering material, said assembly comprising a plurality of mobile electrodes movable over a surface of the covering material and adapted to make continuous electrical contact therewith during such movement, potential difference measuring means conductively connected to selected 30 electrodes of the plurality of mobile electrodes and configured for measuring a potential difference there between, configuration means arranged for configuring connections between electrodes from the plurality of mobile electrodes and the potential difference measuring means, and 35 indicator means arranged for indicating a change in measured potential difference during movement of the mobile electrodes. In this embodiment all electrodes may be mobile, 3 thus avoiding the need to interrupt measuring PDs to displace a stationary or fixed electrode and facilitating measuring PDs in different areas. Typically thousands of measurements may be performed per second, enabling 5 relatively high speed movement of the electrodes while obtaining a high resolution image of subsurface structures. An A/D converter can be used to convert analog measurements of PDs between electrodes into digital signals suitable for further processing such as digital map creation and/or 10 calculations by a computer. The connections between electrodes and the measuring means are configured by the configuration means which may, for each measurement, enable or disable individual connections, reverse two connections to the measuring means and/or connect several individual 15 electrodes together to form a combined electrode.

Advantageously the configuration means allow measurements between any pair of electrodes or groups thereof, providing a way to measure over different areas in the neighborhood of the electrodes without having to move the electrodes.

20 In an embodiment the configuration means are further arranged for selecting one of the plurality of electrodes as a measuring electrode and combining the other electrodes from the plurality of electrodes for providing a reference potential.

25 In an embodiment the configuration means are arranged for combining the other electrodes for providing a reference potential as an average of potential difference measurements made between the measuring electrode and the other electrodes. Such an average can help to cancel out 30 noise in individual measurements.

In an embodiment the configuration means are further arranged for cyclically selecting each of the plurality of electrodes as the measuring electrode. For example, if an embodiment of the detection assembly 35 comprises 7 electrodes ei..e7 and the potential differences between electrodes i and j is given by pirj, then electrode ei is first selected by the configuration means as the 4 measuring electrode. The PDs between ei and the other electrodes are then measured, resulting in values for Pi,j. These values may then be averaged to provide an average potential difference for ex. During the following cycle e2 is 5 selected as the measuring electrode and potential differences are measured between e2 and the other electrodes. This process continues until all 7 electrodes have been selected as a measuring electrode.

In an embodiment the detection assembly further 10 comprises tool for displacing covering material, said tool comprising a part arranged for movably contacting the covering material, wherein said part comprises the mobile electrode or the mobile electrodes. When excavating, for example at an archeological dig or at a construction site, 15 is especially useful to be able to keep on excavating without having to stop every so often to check the current position on maps of earlier surveys for submerged objects. It is also desirable to be able to start digging right away, without having to meticulously survey the area but without 20 the risk of hitting a submerged object. The present invention integrates the measuring electrodes with a part of tool which contacts the material to be excavated so that at the moment the tool contacts the covering material, but before it substantially pierces the material, a measurement 25 of PD can be done to determine whether or not a subsurface object is present.

In an embodiment the tool further comprises a shaft and/or a handle on or near which indicator means are located, said tool preferably comprising a spade or a rake.

30 This embodiment provides a portable tool for moving material, which can instantly give its operator information about the material under the surface he or she is working on. The fact that the assembly according to the invention requires only low voltages to work and is capable of rapidly 35 detecting relatively small objects thanks to the many measurements per square meter that can be made, makes this embodiment a safe and convenient solution especially when 5 digging in close quarters or small areas.

An embodiment further comprises a frame arranged for supporting said electrodes in a substantially fixed position with respect to the frame during movement of the 5 frame. Such a frame may be a flexible frame which can adapt to some extend to the surface is dragged along, or a more rigid frame when the surface to be inspected is relatively smooth. Preferably the electrodes are arranged in a row on the frame said row preferably oriented perpendicular to the 10 direction of movement of the frame. An alternative exemplary embodiment comprises a harrow-like structure which can be towed behind a vehicle, the tines of the harrow comprising the electrodes. The known position of the electrodes relative to each other can be used in further processing of 15 data obtained using the assembly. Also, in case of availability of GPS receivers for surveying, one GPS

receiver would be needed on the frame to be able to derive the position for each electrode.

In an embodiment the frame is made from a 20 substantially anti-static material. The use of a anti-static material provides an advantage when the frame is dragged through a field. When using other materials the friction of the frame with the surface could lead to a build up of static electricity which in turn might affect or distort the 25 accuracy measurements of PDs between electrodes.

In an embodiment the electrodes have indicator means associated with them. In an further embodiment the indicator means are arranged spatially closer to their associated electrodes than to other electrodes. A magnitude 30 of the indication given off by an indicator means may thus advantageously provide information about the subsurface structure closer to said indicator means than to any other indicator means. For instance, when the indicator means comprise LEDs mounted on or close to associated electrodes 35 of supported by a frame as mentioned in an earlier embodiment, a quick look at the indicator means is sufficient to form an approximation of the subsurface 6 structures lying under said frame. When searching for buried pipes or cables, the frame may be used to get a rough idea of where to look, after which a hand held tool according to the invention can be used to expose the pipe or cables.

5 Extra data processing steps can thus be omitted, providing a simple solution for locating submerged objects.

In an embodiment at least several of the electrodes are positioned with respect to each other in a configuration substantially non-collinear with the direction 10 of movement, preferably perpendicular to the direction of movement. The total area covered by the electrodes during and after movement is thus larger than when the electrodes are placed in a line parallel to the direction of movement.

In an embodiment the indicator means are adapted 15 to give off a warning indication when an absolute difference between measured potential differences exceeds a threshold value. Besides the continuously available indication of the change in measured PDs, this embodiment provides a separate warning when the change in PDs indicates for example that an 20 operator using a spade according to the invention is close to hitting a submerged object.

In an embodiment at least some, preferably all electrodes have similar metallurgical and/or electrochemical properties. By using electrodes with similar metallurgical 25 properties, such as a similar standard potential, measurement of a PD between the electrodes will be less likely to be influenced by reduction or oxidation reactions between the electrodes themselves. Conversely, known differences between standard potentials of electrodes with 30 dissimilar metallurgical properties may be used to improve the accuracy of measurements. For instance it is conceivable to choose electrodes which are best suited for a specific covering material, as might be empirically determined or be based on properties of the covering material such as its pH 35 value.

According to a third aspect the invention provides a method for detecting an object submerged in a covering 7 material using a detection assembly as described herein, said method comprising the steps of placing the reference electrode in a stationary position in conductive contact with the covering material, contactingly moving the mobile 5 electrode over the surface of the covering material, and measuring a potential difference between the mobile electrode and the stationary electrode. For example, the typical manner in which a person digging in an area in which pipes and cables are buried might work is to insert one or 10 more reference electrodes (e.g. metal pins) into the ground close to the area where he wants to dig. He then lightly contacts the surface of the area he wants to dig with the blade of a spade according to the invention, and subsequently drags the blade of the spade towards himself. 15 If the indicator means indicate that an absolute difference between PDs measured during movement is above a threshold value then it is likely that there is an object submerged near the blade and the spot can be avoided or, conversely the object can be dug up.

20 An embodiment of the method for detecting an object submerged in a covering material comprises the steps of placing the plurality of mobile electrodes in conductive contact with the covering material, contactingly moving these mobile electrodes over a surface of the covering 25 material, selecting one of the plurality of electrodes as a measuring electrode and combining the other electrodes for providing a reference, determining a potential difference between the measuring electrode and the reference. It may be advantageous to combine electrodes, for instance when 30 measurements for single electrode are very noisy. The larger surface of combined electrodes may help to cancel out such noise.

An embodiment of the method for detecting an object submerged in a covering material comprises the steps 35 of placing the plurality of mobile electrodes in conductive contact with the covering material, contactingly moving these mobile electrodes over a surface of the covering 8 material, selecting one of the plurality of electrodes as a measuring electrode and selecting another one of the plurality of electrodes as a reference electrode, measuring a potential difference between the measuring electrode and 5 the reference electrode. Multiple measurements can thus be obtained for further processing.

An embodiment of the method further comprises the steps of cyclically selecting each of the other electrodes as a reference electrode, measuring for each of the selected 10 reference electrodes a potential difference between said reference electrode and the measuring electrode, and determining an average of the measured potential differences for said measuring electrode. In this manner, an average potential difference is determined between a measuring 15 electrode and all other electrodes, i.e. all electrodes except the measuring electrode.

In an embodiment the method further comprises the step of cyclically selecting each of the plurality of electrodes as a measuring electrode. I.e. each of the 20 electrodes is used at least once as a measuring electrode.

In an embodiment the method further comprises the step of determining an average potential of the other electrodes for providing an average reference potential.

The various aspects and features described and 25 shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications.

30

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of 35 an exemplary embodiment shown in the attached drawings, in which:

Figure la shows a detection assembly according to 9 the present invention in a first position removed from a submerged object, figure lb shows the detection assembly of figure la moved to a second position closer to a submerged object, 5 figure lc shows said detection assembly moved to a third position removed from the submerged object.

figure 2a shows a schematic diagram of a detection assembly according to the invention, having a stationary electrode conductively connected to a covering material 10 surface and a mobile electrode, both electrodes being connected to a potential difference measuring means, figure 2b shows a schematic diagram of a detection assembly similar to the assembly show in figure 2a, however comprising a plurality of mobile electrodes, 15 figure 2c shows a schematic diagram of a detection assembly comprising a plurality of mobile electrodes, figure 3 shows an exemplary embodiment of a detection assembly according to the invention, figure 4a shows another exemplary embodiment of a 20 detection assembly according to the invention, figure 4b shows a graph of potential differences as may be measured by the embodiment in figure 4a.

25 DETAILED DESCRIPTION OF THE INVENTION

A volume of earth in which an object with differing electrical properties, in this case a plastic pipe 2, is buried is shown in figure la, along with a detection 30 assembly according to the invention. The detection assembly comprises a spade 3 for displacing the earth, said spade comprising a handle 4, a shaft 5, and a blade 6. The blade comprises or forms a mobile electrode 7, which is conductively connected to potential difference measuring 35 means 8, by means of an insulated wire 9. The potential difference measuring means are also conductively connected to a reference electrode 10, in this case a metal pin having 10 metallurgical properties similar to the reference electrode, placed contactingly and stationary with the earth.

The shaft and the handle are electrically insulated from the mobile electrode so that the mobile 5 electrode may only form an electrical circuit with the reference electrode through the earth. Though the PD measuring means shown in this exemplary embodiment are positioned at the stationary electrode they may just as well be integrated in the spade, as long as they are conductively 10 placed between both electrodes. The spade may further comprise a GPS receiver or the like for determining an approximate location of the blade. The handle of the spade comprises indicating means (not shown) arranged to indicate a change in measured PD during movement of the spade. When 15 an operator drags the blade of the spade across the earth along a direction D, at some point the blade will be close enough to the submerged object for the object to influence the PD measured between the electrode on the blade and the stationary electrode, as is the case in figure lb. As a 20 result the indicating means give off an indicating signal 11, in this case sound, to warn the operator of a change in structure in the ground beneath the blade of the spade. Such a sound might have a frequency proportional to the detected change in PD. Alternatively the indicating means may 25 comprise a graphical display showing the difference in PD as well as other data useful during digging, such as location and a map of known structures. When the absolute difference between recently measured and earlier measured PDs exceeds a predetermined or adaptively calculated threshold value, the 30 indicator means may also give a more obtrusive warning to alert an operator of changes in the subsurface structure.

In figure lc the blade of the spade has moved to a third position which is again sufficiently removed from the submerged plastic pipe 2 for the absolute difference between 35 measured PDs not to exceed the threshold, and therefore not giving off a warning.

If figure 2a a schematic diagram of a detection 11 assembly according to the invention is show. A stationary reference electrode eo is conductively to the ground and to potential difference measuring means 23. The potential difference measuring means in turn are conductively 5 connected to mobile electrode ei and arranged to measure a PD between the reference electrode and the mobile electrode. The connections may be made using insulated conductive wires .

In figure 2b, a similar detection assembly is 10 show, however comprising multiple mobile electrodes ei-e^ and associated potential difference measuring means for measuring a PD between the reference electrode and mobile electrodes. It is also conceivable that only one potential difference measuring means is used, of which the connections 15 are rapidly switched to different electrodes in order to make measurements between different electrode pairs. Advantageously these measurements can be averaged to cancel out noise. Furthermore in case one of the mobile electrodes is damaged or does not make contact with the covering 20 material during measurement, there are still other mobile electrodes from which data can be obtained.

In figure 2c the stationary electrode has been dispensed with altogether. The assembly according to this embodiment may calculate an average potential difference for 25 each of the electrodes with the other electrodes. I.e. the average potential difference for mobile electrode e3 is the average of the measured potential differences p3,i uptil p3,7· In figure 3 an embodiment according to the invention is shown in the form of a rake 31 comprising a multitude of 30 tines 32, each of which may comprise an electrode. The rake can be connected to a stationary electrode as was the spade from figures la-lc, but may also comprise a plurality of mobile electrodes instead. In the latter case the rake may advantageously comprise configuration means for configuring 35 connections of the electrodes; in this manner multiple measurements can be made of PDs between multiple pairs of electrodes. For example, if the PD between electrodes e3 and 12 e4 is significantly larger that the PD between other pairs of neighboring electrodes it is likely that there is a change in subsurface structure close to the position of the electrode e5 and/or e4. Additionally, indicator means may be 5 placed on upper part of the tines of the rake, preferably LEDs, which indicate the relative PDs of neighboring pairs of electrodes. It is thus possible to survey the subsurface at a glance without having to use a fixed or difficult to move electrode, simply by raking the surface.

10 In figure 4 another exemplary embodiment according to the invention is shown, this particular embodiment being more suitable for surveying larger areas in detail. The embodiment shown has a frame 40 made from a substantially non-conductive and anti-static material. On the frame a 15 plurality of electrodes 41, preferably arranged equidistantly, is supported. Each of the electrodes has associated indicator means 43, in this case LEDs, for indicating a PD measured between the electrode and other electrodes. The LEDs are connected to amplifiers (not show), 20 which amplify the measured PDs and supply a current to power the LEDs. When the frame is placed stationary on surface area to be inspected, the LEDs give an indication of the distribution of the PD under the surface covered by the frame. When the frame is dragged behind a vehicle, using 25 tow-eye 42 to attach the frame to the vehicle, larger areas of ground can consecutively be covered. Though in principle a single row of electrodes perpendicular to the direction of movement of the frame suffices to gather data for building a map, in may also be convenient to have several of such rows 30 placed next to each other in the direction of movement. In figure 4A this would be after the cut-off line. In such a case, when the frame moves over a pipe or cable, the light signals from the LEDs seem to propagate over the rows, providing a much more intuitive representation of the 35 subsurface than when the electrodes are arranged in a single row.

Figure 4B shows a PD graph superimposed on an 13 image of a pipe buried in the ground. Along the z-axis an indication of the change in measured PD is given. The x- and y-axis represent coordinates on the surface of covering material. The surface in question may be a flat surface; the 5 z-coordinate shows the measured PD-values, not the height of the surface. As can clearly be seen, there is a sudden change in measured PD values in the area under which the pipe is buried. This change in PD can be used successfully to detect submerged objects.

10 Obviously, these exemplary embodiments may be elaborated upon, for example by adding several kinds of locating means, storage for measured data and advanced signal processing devices. Such elaborations are widely known in the art and are included herein implicitly.

15 Furthermore, although the above described examples are all related to the survey for items buried in a volume of earth, the device and method is also applicable to survey for items submerged in water and/or buried in a volume of earth submerged in water.

20 It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be 25 encompassed by the spirit and scope of the present invention.

Claims

A detection assembly for detecting an object sunk into a covering material, the assembly comprising: a movable electrode movable over a surface of the covering material and adapted to make continuous electrical contact therewith during such a movement, a reference electrode which contacts the covering material, means for measuring a potential difference conductively connected to the electrodes and adapted to measure a potential difference between the movable and the reference electrode, indicating means adapted to indicate a change in measured potential difference .

2. Detection assembly according to claim 1, wherein the reference electrode is arranged to be stationary with respect to the covering material and the movable electrode is movable with respect to the stationary reference electrode.

3. Detection assembly for detecting an object sunk into a covering material, the assembly comprising: a plurality of movable electrodes movable over a surface of the covering material and arranged to make continuous electrical contact therewith during such movement, means for measuring a potential difference conductively connected to selected electrodes 30 from the plurality of movable electrodes and adapted to measure a potential difference therebetween, 2002124 configuration means adapted to configure connections between electrodes of the plurality of movable electrodes and the means for measuring a potential difference, indicating means adapted to indicate a change in measured potential difference.

4. Detection assembly according to claim 3, wherein the configuration means are further adapted to select one from the plurality of electrodes as a measuring electrode and to combine the other electrodes from the plurality of electrodes to provide a reference potential.

5. Detection assembly as claimed in claim 4, wherein the configuration means are adapted to combine the other electrodes to provide a reference potential as an average of potential difference measurements made between the measuring electrode and the other electrodes.

6. Detection assembly according to claim 5, wherein the configuration means are further adapted to cyclically select the measuring electrode for each of the plurality of electrodes.

7. Detection assembly according to any one of the preceding claims, further comprising a tool for moving covering material, wherein the tool comprises a part adapted to make movable contact with the covering material, wherein the part comprises the movable electrode or movable electrodes.

8. Detection assembly according to claim 7, wherein the tool further comprises a handle and / or a handle at or near where the indicating means are placed, the tool preferably comprising a shovel or a rake.

9. Detection assembly as claimed in any of the foregoing claims, wherein the assembly further comprises a frame adapted to support electrodes in a substantially fixed position relative to the frame during movement of the frame.

The detection assembly of claim 9, wherein the frame is made of a substantially antistatic material.

11. Detection assembly as claimed in any of the foregoing claims, wherein electrodes have indicating means that are associated with the electrodes.

12. Detection assembly according to claim 11, wherein the indicating means are spatially closer to their associated electrodes than to other electrodes.

13. Detection assembly as claimed in any of the foregoing claims, wherein at least one of the electrodes is placed relative to each other in a configuration substantially non-collinear with the direction of movement, preferably perpendicular to the direction of movement.

14. Detection assembly as claimed in any of the foregoing claims, wherein the indicating means are adapted to give a warning indication when an absolute difference between measured potential differences exceeds a threshold value.

15. Detection assembly as claimed in any of the foregoing claims, wherein at least some of the electrodes have corresponding metallurgical properties, preferably all electrodes.

16. Method for detecting an object sunk into a covering material using a detection assembly as described in claim 1 or claim 2, wherein the method comprises the steps of: placing the reference electrode in a fixed position in conductive contact with the covering material, contacting movement of the movable electrode over the surface of the covering material, measuring a potential difference between the movable electrode and the fixed electrode.

17. A method for detecting an object sunk into a covering material using a detection assembly as described in claim 3, wherein the method comprises the steps of: placing the plurality of movable electrodes in conductive contact with the covering material, contacting movement of these movable electrodes over a surface of the covering material, selecting one from the plurality of electrodes as a measuring electrode and combining the other electrodes to provide a reference, determining a potential difference between the measuring electrode and the reference.

18. A method of detecting an object sunk into a covering material using a detection assembly as described in claim 3, wherein the method comprises the steps of: placing the plurality of movable electrodes in conductive contact with the covering material, contacting movement of these movable electrodes over a surface of the covering material, selecting one of the plurality of electrodes as a measuring electrode and selecting at least one of the other electrodes from the plurality of electrodes as a reference electrode, measuring a potential difference between the measuring electrode and the reference electrode.

19. Method according to claim 18, further comprising the steps of: cyclically selecting as each reference electrode a reference electrode for each of the selected reference electrodes, measuring a potential difference between the reference electrode and the measuring electrode for each of the selected reference electrodes. determining an average of the measured potential differences for the measuring electrode.

The method of claim 17, 18 or 19, further comprising the step of cyclically selecting as a measuring electrode each of the plurality of electrodes.

The method of claim 20, further comprising the step of determining an average potential of the other electrodes to provide an average reference potential. -o-o-o-o-o-o-o-2002124