Device and method for detecting electrically conducting objects to be measured in a ground

Abstract

A device (10) for detecting electrically conducting objects to be measured in a ground is provided, including a housing (21), a solenoid unit (34) situated in the housing (21), which includes a transmitter coil unit (38) and a receiver coil unit (39), a control unit (36), and an evaluation unit (37). A metal sheet (35) is provided in the housing (21), the solenoid unit (34) being situated on a lower side (53) of the metal sheet (35) facing the ground during the measuring operation, and the control unit (36) being situated on an upper side (54) of the metal sheet (35) facing away from the ground during the measuring operation.

Claims

1. A device for detecting electrically conducting objects to be measured in a ground, the device being moved over a surface of the ground during the measuring operation in a measuring orientation, the device comprising: a housing; a solenoid unit situated in the housing, the solenoid unit including a transmitter coil unit including at least one transmitter coil and including a receiver coil unit including at least one receiver coil; a control unit connected to the solenoid unit and designed to control the transmitter coil unit and to control the receiver control unit; an evaluation unit connected to the solenoid unit and designed to process and evaluate a voltage induced in the receiver control unit as a measuring signal; and a metal sheet in the housing having a sheet metal thickness (d), the metal sheet being situated in parallel to the surface of the ground during the measuring operation, the solenoid unit being situated on a lower side of the metal sheet facing the ground during the measuring operation, and the control unit being situated on an upper side of the metal sheet facing away from the ground during the measuring operation.

2. The device as recited in claim 1 wherein the evaluation unit includes a first evaluation unit processing the measuring signals, and a second evaluation unit evaluating the measuring signals, the first evaluation unit being situated on the upper side of the metal sheet facing away from the ground during the measuring operation.

3. The device as recited in claim 2 wherein the second evaluation unit is situated on the upper side of the metal sheet facing away from the ground during the measuring operation.

4. The device as recited in claim 2 wherein the second evaluation unit is situated outside the housing, the first and second evaluation units being connectable via a communication link.

5. The device as recited in claim 2 wherein the housing encloses an interior, and the metal sheet divides the interior into a lower portion and an upper portion, the solenoid unit being situated in the lower portion, and the control unit and the first evaluation unit being situated in the upper portion.

6. The device as recited in claim 1 wherein the housing encloses an interior, and the metal sheet divides the interior into a lower portion and an upper portion, the solenoid unit being situated in the lower portion, and the control unit being situated in the upper portion.

7. The device as recited in claim 1 further comprising a display unit including a display designed to display a measuring result calculated by the evaluation unit, the display being situated on the upper side of the metal sheet facing away from the ground during the measuring operation.

8. The device as recited in claim 2 further comprising a memory unit connected to the evaluation unit in a data-transmitting manner, a calibration signal being stored in the memory unit, the calibration signal having been ascertained in the absence of electrically conducting objects to be measured.

9. The device as recited in claim 1 wherein the metal sheet is made of aluminum, the metal sheet having a sheet metal thickness (d) of at least 1.0 mm.

10. The device as recited in claim 9 wherein the metal sheet has a sheet metal thickness (d) of at least 2.0 mm.

11. The device as recited in claim 1 wherein the metal sheet is made of copper, the metal sheet having a sheet metal thickness (d) of at least 0.4 mm.

12. The device as recited in claim 11 wherein the metal sheet has a sheet metal thickness (d) of at least 0.8 mm.

13. A method for detecting electrically conducting objects to be measured in a ground using the device as recited in claim 11, the method comprising a step sequence of the following steps: flowing a current (I) through at least one transmitter coil of the transmitter coil unit; switching off the current (I) by the control unit at a switch-off point in time (t.sub.0); recording a voltage, induced in the at least one receiver coil of the receiver coil unit, by the evaluation unit with a time shift (Δt) after the switch-off point in time (t.sub.0) of the current (I) as a measuring signal; and determining a difference signal by the evaluation unit as a difference between the measuring signal and a stored calibration signal, the calibration signal having been ascertained in the absence of electrically conducting objects to be measured.

14. The method as recited in claim 3 wherein the time shift (Δt) is not smaller than 5 μs.

15. The method as recited in claim 3 wherein the time shift (Δt) is not greater than 10 μs.

16. The device as recited in claim 1 wherein the housing has a lower housing shell and a housing cover enclosing an interior, the metal sheet being in the interior.

17. The device as recited in claim 16 wherein the solenoid unit and the control unit are in the interior.

18. The device as recited in claim 17 wherein the evaluation unit is in the interior.

19. The device as recited in claim 16 further comprising a handle situated above the housing cover.

20. The device as recited in claim 1 further comprising wheels connected to the housing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the present invention are described hereafter based on the drawings. They are not necessarily intended to represent the exemplary embodiments true to scale; rather, the drawings, where useful for explanation, is implemented in a schematic and/or slightly distorted form. It must be taken into consideration in this that a variety of modifications and changes regarding the shape and the detail of a specific embodiment may be carried out, without departing from the general idea of the present invention. The general idea of the present invention is not limited to the exact shape or the detail of the preferred specific embodiment shown and described hereafter, or limited to a subject matter which would be limited compared to the subject matter claimed in the claims. For given dimensional ranges, values within the described limits shall also be disclosed as limiting values and arbitrarily usable and claimable. For the sake of simplicity, identical reference numerals are used hereafter for identical or similar parts or parts having an identical or similar function.

(2) FIG. 1 shows the use of a device according to the present invention for detecting electrically conducting objects to be measured in a ground;

(3) FIGS. 2A, B show the device according to the present invention of FIG. 1 in a three-dimensional representation (FIG. 2A) and the essential components of the device, which include a housing, a solenoid unit, a metal sheet, control and evaluation units, and a display unit including a display, in an exploded view (FIG. 2B);

(4) FIG. 3 shows the arrangement of the components of the device according to the present invention in the housing in a schematic representation;

(5) FIG. 4 shows the time curve of a measuring signal, a calibration signal and a difference signal;

(6) FIGS. 5A, B show the time curves of the standardized calibration signals for three aluminum sheets having different sheet metal thicknesses (FIG. 5A), and the time curves of the standardized calibration signals for three copper sheets having different sheet metal thicknesses (FIG. 5B); and

(7) FIG. 6 shows the curve of the integral of the standardized calibration signal of FIGS. 5A, B as a function of sheet metal thickness d of the metal sheet for aluminum sheets and copper sheets.

DETAILED DESCRIPTION

(8) FIG. 1 shows the use of a device 10 according to the present invention for detecting electrically conducting objects to be measured 11 in a ground 12. Device 10 may be designed as a held or guided detection device. A held detection device is held without feed movement over a surface 13 of ground 12 to be detected, and a guided detection device is guided along a linear path or an arbitrary path over surface 13 of ground 12 to be detected. A detection device which is held or guided over surface 13 of ground 12 to be detected by an operator using his/her hand is referred to as being hand-held or hand-guided. FIG. 1 shows a hand-guided detection device 10, which is moved along a feed direction 14 over surface 13 of ground 12.

(9) FIGS. 2A, B show device 10 according to the present invention in a three-dimensional representation (FIG. 2A) and the essential components of device 10 in an exploded view (FIG. 2B).

(10) FIG. 2A shows device 10 in the assembled state. Device 10 includes a housing 21, a handle 22, a battery 23, a moving unit 24 including four wheels 25, a display unit 26 including a display 27, an operating unit 28, and data interfaces 29. The user guides device 10 with the aid of handle 22 and moving unit in feed direction 14 over ground 12 to be detected, which is designed as a ground floor, for example.

(11) FIG. 2B shows the essential components of device 10 according to the present invention in an exploded view. In the exemplary embodiment, device 10 includes five assemblies, which are inserted into one another and assembled. Housing 21 is made up of a lower housing shell 31, which is connected to moving unit 24, and an upper housing cover 32, which is connected to display unit 26. When assembled, housing shell 31 and housing cover 32 enclose an interior 33, in which a solenoid unit 34, a metal sheet 35, a control unit 36 and an evaluation unit 37 are situated.

(12) Solenoid unit 34 includes a transmitter coil unit 38, which includes one or multiple transmitter coil(s), and a receiver coil unit 39, which includes one or multiple receiver coil(s). The number of the transmitter and receiver coils, the size and shape of the transmitter and receiver coils, and the spatial orientation of the transmitter and receiver coils are usually adapted to electrically conducting objects to be measured 11 to be detected, which are to be measured with the aid of device 10 according to the present invention. The idea of device 10 according to the present invention is independent of the design of transmitter coil unit 38 and of receiver coil unit 39.

(13) Control unit 36 is designed to control transmitter coil unit 38 and receiver coil unit 39 and is circuitry-wise connected to solenoid unit 34. Evaluation unit 37 is designed to evaluate the voltage induced in the receiver coils and is circuitry-wise connected to solenoid unit 34. The term “evaluation unit” covers all components for the signal and measured value processing of the received signals, such as amplifiers, filters or analog-to-digital converters. Control unit 36 and evaluation unit 37 are integrated into a checking unit 41 in the exemplary embodiment.

(14) Metal sheet 35 may have multiple boreholes, which may be designed as blind boreholes or through-boreholes. The boreholes are used, on the one hand, as retaining points for the transmitter and receiver coils of solenoid unit 34 and, on the other hand, as passages for the circuitry-wise connection of solenoid unit 34 to control unit 36 and evaluation unit 37.

(15) FIG. 3 shows the arrangement of the components of device 10 according to the present invention in housing 21 in a schematic representation. Metal sheet 35 divides interior 33 of housing 21 into a lower portion 51, which faces ground 12 to be detected during the measuring operation of device 10, and an upper portion 52, which faces away from ground 12 to be detected during the measuring operation of device 10. Solenoid unit 34 including transmitter coil unit 38 and receiver coil unit 39 is situated in lower portion 51 of interior 33, and control unit 36 and evaluation unit 37 are situated in upper portion 52 of interior 33.

(16) In principle, it applies with respect to the arrangement of the components of the device that solenoid unit 34 is situated on a lower side 53 of metal sheet 35 facing ground 12. All further components of device 10 which include conducting materials and represent electrically conducting interfering objects are situated on an upper side 54 of metal sheet 35 facing away from ground 12. In addition to control unit 36 and evaluation unit 37, this includes display unit 26 including display 27, operating unit 28, data interfaces 29, and battery 23. Handle 22 is situated above housing cover 32, so that electrically conducting foreign objects, such as a watch, rings or other pieces of jewelry which an operator wears during the measuring operation of device 10, are situated on the far side of upper side 53 of metal sheet 35.

(17) Metal sheet 35 is made of a metal, in principle all metals being suitable. Aluminum, which is designed as pure aluminum or aluminum alloy, and copper, which is designed as pure copper or copper alloy, are particularly suitable metals for metal sheet 35. The term “metal” covers pure metals and metal alloys. The action of metal sheet 35 is dependent on several variables. These include electrical conductivity σ of the metal, magnetic permeability μ of the metal, and sheet metal thickness d of metal sheet 35. Electrical conductivity σ and magnetic permeability μ are established by the selection of a metal, sheet metal thickness d of metal sheet 35 may be varied for an established metal. The decay behavior of the eddy currents in metal sheet 35 may be influenced via the selection of sheet metal thickness d of metal sheet 35.

(18) In the exemplary embodiment, transmitter coil unit 38 includes one transmitter coil 55, and receiver coil unit 39 includes multiple receiver coils 56. As an alternative, transmitter coil unit 38 may include multiple transmitter coils 55 or receiver coil unit 39 may include one receiver coil 56. The number, orientation and/or size of transmitter coils 55 and the number, orientation and/or size of receiver coils 56 are adapted to electrically conducting objects to be measured 11 which are to be measured with the aid of device 10 according to the present invention. The idea of device 10 according to the present invention is independent of the design of transmitter coil unit 38 and of receiver coil unit 39.

(19) A current I flows through transmitter coil 55, which generates a primary magnetic field. Current I is switched off by control unit 36, so that the primary magnetic field decays. When the current is switched off, the primary magnetic field induces eddy currents in electrically conducting objects which generate secondary magnetic fields, the secondary magnetic fields decaying considerably more slowly than the primary magnetic field. The primary magnetic field is superimposed with the secondary magnetic fields of the electrically conducting objects to form a resulting magnetic field.

(20) Metal sheet 35 and the measuring method must be matched to one another in such a way that, during the recording of the measuring signals, on the one hand the undesirable eddy currents generated by electrically conducting foreign and interfering objects have sufficiently decayed and, on the other hand, the desirable currents generated by electrically conducting objects to be measured 11 in ground 12 have not yet excessively decayed.

(21) The evaluation unit 37 comprises a first evaluation unit 37A and a second evaluation unit 37B. The first evaluation unit 37A is connected to the receiver coil unit 39 and is designed to process the measuring signals. The second evaluation unit 37B is connected to the first evaluation unit 37A and is designed to evaluate the processed measuring signals. The first evaluation unit 37A processes the measuring signals, the processed measuring signals are transmitted via a communication link 42 to the second evaluation unit 37B, and the second evaluation unit 37B evaluates the processed measuring signals. The communication link 42 may be designed as a wireless or wired communication link. In the exemplary embodiment, the communication link 42 is designed as a wired communication link. The evaluation unit 37 is connected in a data-transmitting manner to a memory unit 43, in which a calibration signal is stored.

(22) FIG. 4 shows the time curve of a measuring signal 61 which was measured with the aid of device 10. To eliminate effects, such as secondary fields of electrically conducting interfering objects, a calibration signal 62 is stored in device 10, which was recorded in the absence of electrically conducting objects to be measured 11 with the aid of device 10. The evaluation is carried out based on a difference signal 63, which is formed by difference creation between measuring signal 61 and calibration signal 62.

(23) Device 10 includes solenoid unit 34 including transmitter coil unit 38 and receiver coil unit 39, control unit 36, and evaluation unit 37 including the first and second evaluation units. During the measuring operation of device 10, a current I flows through transmitter coils 55, and current I is switched off by control unit 36 at a switch-off point in time t.sub.0. Voltages are induced in receiver coils 56, which are recorded as received signals by evaluation unit 37. The received signals of receiver coil unit 38 are referred to as calibration signals in the absence of electrically conducting objects to be measured 11, and as measuring signals in the presence of electrically conducting objects to be measured 11.

(24) Evaluation unit 37 of device 10 according to the present invention influences the measuring method insofar as evaluation unit 37 has an overload limit for the received signals. The overload limit is a variable of evaluation unit 37 indicating when an overload of evaluation unit 37 occurs. The overload limit is dependent, for example, on the reference voltage of the analog-to-digital converters of the evaluation unit. Input voltages of the analog-to-digital converters greater than this reference voltage result in an overload. The level of the input voltages depends on the strength of the magnetic field of the eddy currents at the location of the receiver coils, the geometry of the receiver coils, and the used amplification. The received signals of receiver coil unit 39 are standardized to the overload limit. A processing and an evaluation of the received signals is only possible below the overload limit; as long as the amplitudes of the received signals are above the overload limit, evaluation unit 37 is not able to carry out any processing and evaluation of the received signals.

(25) Measuring signal 61 and calibration signal 62 generally have similar time curves. After the current is switched off in transmitter coil unit 38, a rapid drop in the amplitudes of the received signals is observable, which transitions to a slower drop. The rapid drop of the received signals occurs immediately after current I is switched off and describes the penetration of the eddy currents from the surface into the interior of the electrically conducting objects. When the eddy currents flow completely through the electrically conducting objects, the rapid drop transitions into a slower drop of the received signals.

(26) FIGS. 5A, B show the time curves of standardized calibration signals 71, 72, 73, 74, 75, 76 for different metal sheets. FIG. 5A shows the time curves of standardized calibration signals 71, 72, 73 for three metal sheets made up of aluminum, which hereafter are referred to as aluminum sheets, and FIG. 5B shows the time curves of standardized calibration signals 74, 75, 76 for three metal sheets made up of copper, which hereafter are referred to as copper sheets.

(27) The aluminum sheets of FIG. 5A are produced from pure aluminum (content of aluminum greater than 99.5%) having an electrical conductivity σ.sub.A of 37.Math.10.sup.6 S/m and a magnetic permeability μ.sub.A of 1.000022 H/m, and differ from one another in the sheet metal thicknesses. The first aluminum sheet has a first sheet metal thickness d.sub.A1 of 0.5 mm, the second aluminum sheet d.sub.A2 has a second sheet metal thickness d.sub.A2 of 1.0 mm, and the third aluminum sheet has a third sheet metal thickness d.sub.A3 of 2.0 mm. The copper sheets of FIG. 5B are produced from pure copper (content of copper greater than 99.5%) having an electrical conductivity σ.sub.B of 58.Math.10.sup.6 S/m and a magnetic permeability μ.sub.B of 0.9999936 H/m, and differ from one another in the sheet metal thicknesses. The first copper sheet has a first sheet metal thickness d.sub.B1 of 0.2 mm, the second copper sheet has a second sheet metal thickness d.sub.B2 of 0.4 mm, and the third copper sheet has a third sheet metal thickness d.sub.B3 of 0.8 mm.

(28) The time curves of standardized calibration signals 71 through 76 show that sheet metal thickness d of metal sheet 35 changes the time curves of the calibration signals. The thicker metal sheet 35, the longer it takes for the eddy currents to flow completely through the electrically conducting objects and for the rapid drop to transition into the slower drop. Time shift Δt after the current is switched off in transmitter coil unit 38 is selected in such a way that the rapid drop of the received signal has decayed. At the same time, time shift Δt must not be selected to be too large since the desirable effects of the electrically conducting objects to be measured in the measuring signals decay at increasing time shift Δt.

(29) At approximately 3 μs, calibration signals 71, 74 transition from the rapid drop to the slower drop, the amplitudes considerably exceeding the overload limit during the transition. Since the amplitudes of calibration signals 71, 74 are also above the overload limit for time shifts Δt greater than 20 μs after the current is switched off, the first aluminum sheet and the first copper sheet are not suitable for the used evaluation unit 37 of device 10.

(30) At approximately 5 μs, calibration signals 72, 75 transition from the rapid drop to the slower drop, the amplitudes insignificantly exceeding the overload limit during the transition. To prevent an overload of evaluation unit 37, the maximum amplitudes should not exceed a maximum value. Since the calibration signals are standardized to the overload limit, the maximum value may be indicated as a percentage of the overload limit (0% to 100%). For example, a percentage of 50% of the overload limit is suitable as a maximum value. For calibration signals 72, 75, the amplitudes only drop below the limit of approximately 50% of the overload limit for time shifts Δt greater than 20 μs, so that the second aluminum sheet and the second copper sheet are only conditionally suitable for the used evaluation unit 37. When a percentage of 70% of the overload limit is defined for the maximum value, instead of the percentage of 50% of the overload limit, the amplitudes drop below the maximum value for calibration signals 72, 75 for time shifts Δt greater than 13 μs. The definition of a suitable maximum value depends, among other things, on evaluation unit 37.

(31) At approximately 6 μs, calibration signals 73, 76 transition from the rapid drop to the slower drop, the amplitudes being already below the overload limit during the transition. For the calibration signals, the amplitudes only drop below the limit of approximately 50% of the overload limit for time shifts greater than 7 μs, so that the third aluminum sheet and the third copper sheet are suitable for the used evaluation unit 37. A value of approximately 7 μs is suitable for calibration signals 73, 76 as time shift Δt after the current is switched off in transmitter coil unit 38. When a percentage of 70% of the overload limit is defined for the maximum value, instead of the percentage of 50% of the overload limit, the amplitudes drop below the maximum value for the calibration signals for time shifts Δt greater than 6 μs.

(32) FIG. 6 shows the standardized curves of the integrated calibration signals from FIGS. 5A, B as a function of sheet metal thickness d of metal sheet 35 for metal sheets made up of aluminum (aluminum sheets) and for metal sheets made up of copper (copper sheets). It should be noted that amplitudes over 1 in FIGS. 5A, B are not measurable due to an overload, and the measured calibration signal has the saturation value 1 in this range. The integrated calibration signals shown in FIG. 6 are also standardized to the overload limit.

(33) The curves of the integrated calibration signals for the used copper sheets show that an overload of evaluation unit 37 occurs for sheet metal thicknesses smaller than 0.35 mm, and favorable measuring conditions exist for sheet metal thicknesses greater than 0.8 mm. With the used aluminum sheets, an overload of evaluation unit 37 occurs for sheet metal thicknesses smaller than 1.0 mm, and favorable measuring conditions exist for sheet metal thicknesses greater than 2.0 mm.