WO1989007775A1

WO1989007775A1 - Metal detector

Info

Publication number: WO1989007775A1
Application number: PCT/CH1989/000022
Authority: WO
Inventors: Dieter Alex Rufer; Walter Egger
Original assignee: Egco Ag
Priority date: 1988-02-12
Filing date: 1989-02-09
Publication date: 1989-08-24
Also published as: CH676051A5; EP0360845A1

Abstract

A metal detector comprises a measuring part (6, 7, 8) and an evaluation part (1). The measuring part produces a variable magnetic field and has a sensor (9) which detects fluctuations in a magnetic field signal due to the reinforcing rods (10, 10', 10'') to be detected. To improve the precision when determining the position of said rods, an auxiliary device with a double coil is provided to produce two variable magnetic fields as desired and to store a physical quantity derived from the magnetic field signal.

Description

M e t a l l s u c h g e rät

The present invention relates to a metal detector according to the preamble of claim 1.

Metal detection devices of this type are primarily used for localizing metal parts laid under a surface, such as reinforcing iron in reinforced concrete or lines and other construction elements in building parts.

Such known metal detection devices prove to be disadvantageous with regard to their accuracy and ease of use, because when the surface is scanned with the Measuring part, the position of the object sought is determined by the maximum of the deflection, which results in a relatively flat signal curve as a function of the scanning path. This means that the surface has to be painted over several times and the determination of the maximum remains relatively imprecise due to its blurring. In addition, it is tiring for the user to look at the pointer of the instrument and at the same time to assess the position and movement of the measuring part.

Most of the time, it is also of interest to know how deep, for example, a reinforcing bar lies below the surface and what diameter it has. This information is only supplied incompletely with the known metal detection devices, since these devices only correctly indicate the depth if the rod diameter is known in advance.

It is therefore an object of the invention to provide an easy-to-use metal detector which allows greater accuracy in determining the position of the metal part sought.

According to the invention, this object is achieved by the measures specified in the characterizing part of claim 1. Advantageous further developments result from the subclaims.

The invention is explained below with reference to a drawing, for example. It shows:

1 is a perspective view of a metal detector according to the invention on a concrete surface,

2 is a perspective view of the measuring part of such a metal detector,

3 shows a schematic illustration of a double coil and a marking device in a sectional view,

Fig. 4 shows the block diagram of an inventive

Metal detector with a measuring part according to Fig. 2, and

5 shows a diagram of the signal curve as a function of the scanning path according to a further embodiment of the invention.

1 comprises an evaluation part 1 with an image output device 2 and one with keys and / or switch-provided field 3. The device 2 can have a cathode ray tube, a liquid crystal dot matrix or other display means. The evaluation part 1 is connected via cables 4 and 5 to a measuring path device 6, 7, 8 or to a probe 9. The device 6, 7, 8, which together with the probe 9 forms the actual measuring part, consists of a part 6, a rotatable guide device 7 and a flexible traction means 8, the part 6 having an unwinding device on the inside.

The metal detector according to FIG. 1 is used, for example, to locate reinforcing bars 10, 10 ', 10 "in a concrete wall 11 and functions as follows:

The probe 9 emits an alternating magnetic field of, for example, 1500 Hz and also serves as a sensor which detects the reactions caused by the reinforcing bars 10, 10 ', 10 "by interactions with the mentioned alternating magnetic field.

With the probe 9, the concrete surface is now swept densely along an indicated scanning path 12. The position of the probe 9 and thus also the scanning path is coordinated measured by means of the device 6, 7, 8 by the smooth traction device 8 is unwound under tension. The traction means 8 can, for example, be a plastic thread that is only slightly stretchable with the probe 9. The unwinding device in the interior of part 6 is connected to a clock disk, from which the distance a between the unwinding part 6 and the probe 9 results from counting the pulses. The guide device 7 is connected to an angle encoder or a timing disk in order to determine the angle σC between a reference direction and the direction of the traction means.

The measurement signal along the scanning path 12 is digitized and stored in connection with the rectangular coordinates calculated from the values of σ and a. Depending on the evaluation program, either the measurement signal is displayed directly in the form of brightness and / or color patterns on the display device, or only the points are displayed which each correspond to an associated extreme value of the measurement signal, that is to say the position of a reinforcing iron. The display device 2 can also be used to indicate numerical values which correspond, for example, to the degree of coverage at the point of a reinforcing bar indicated by the position of the probe on the screen. Of course, one could Printer / plotter can be connected to get the image on any scale.

FIG. 2 shows a measuring part 21 with the omission of part of the upper cover, which contains a marking device. The measuring part 21 has two wheels 22, 22 ', which are coupled via a common axis 23, in order to effect a guidance in a straight direction when rolling off, wherein a rail could also be provided for guidance along a straight line for the same purpose. The wheels have a non-slip surface and a well-defined radius, for example in that the wheel is made of hard material and the rolling surface of the wheel contains a groove in which a soft and non-slip rubber ring is inserted. The measuring part 21 is provided with a displacement measuring device consisting of a clock disc 24 driven by the axis 23 and a double fork light barrier 25 and with a coil 26 serving as a sensor, which represents the actual metal detector. The measuring part 21 connected to an evaluation part via a connecting cable 27 serves to locate a reinforcing bar 29 in a concrete wall 28. The front side of the measuring part 21 is provided with switches and / or keys 19 and, if appropriate, with light-emitting diodes 18. The displacement measuring device functions in such a way that, when the axis 23 rotates, the double fork light barrier 25 generates two signals, for example 90 ° out of phase, by interaction with the clock disk 24, from which the scanning path traversed can be determined in order to determine the position of the metal part determine. For this purpose, the metal detector has an auxiliary device which is based on the continuous storage of values of at least one physical quantity in order to subsequently determine the positions which correspond to the extreme values of the measurement signal, the physical quantity being an electrical analog or digital signal or a mechanical-geometric position.

2 now works as follows:

After commissioning, an adjustment is carried out automatically by pressing a button on the suspended evaluation part and when the measuring part is further away from metallic objects. The measuring part 21 is then placed on the surface to be examined and one of the keys 19 prepares for the start of a measurement. Now the measuring part 21 is moved by hand with slight pressure on the surface in a first direction, for example from from left to right. The rigidly coupled wheels 22 and 22 "result in a straight guidance of the movement. The measuring signal that is created is automatically electronically stored point by point and in function of the scanning path that is traversed. If the direction of movement is reversed, the electronic circuit recognizes this and during a After a short waiting time, the positions of those values along the scanning path where there is a signal maximum or minimum are calculated from the point-by-point stored measurement curve. When moving backwards, the position of the reinforcing iron is then indicated at these points by a light-emitting diode Several positions, under which a reinforcement bar is located, can be specified in a short time and with high accuracy.Additional information about the diameter of the reinforcement bar and the depth below the surface are indicated at the corresponding locations on the display of the evaluation part and if necessary printed out on a paper strip.

The double coil of a measuring part 21 according to FIG. 3 has a ferrite shell core 31 with an inner winding 32 and / or an unconventional outer winding 33. An optional marking device comprises a solution 34 with a fiber pen 35 with a dye-soaked writing tip 36. The fiber pen 35 is pressed in the non-activated state by a spiral spring 37 against a stop of the socket 34. The socket 34 can, for example, be mounted on the measuring part and can preferably be unscrewed for removal when not in use. In addition to the shell core 31 and the windings 32, 33, all other elements of the double coil and the marking device are preferably made of non-metallic and non-magnetic material.

The double coil allows a switchover from the inner winding 32 to the outer coil 33 in order to obtain additional information from the two magnetic fields which differ in the course of the field lines, which allows not only the depth but also the diameter of the reinforcement rod to calculate. The felt pen 35 is pressed down when the measuring part or the probe 21 (FIG. 2) is exactly over a reinforcing bar in order to conveniently mark the surface of the concrete slab 28 there, under which a piece of metal is located.

The exact position of the reinforcing iron 29 is calculated according to the invention from the stored measurement values and at the backward movement of the measuring part 21 is displayed, for example, by means of a light-emitting diode 18. The measuring part 21, which is preferably provided with a double coil according to FIG. 3, could also be implemented with one or more coils with or without core material. A solution with a ferrite rod would have the advantage that additional information could be obtained by an axial movement of the probe.

Of course, one could replace the felt pen 35 or the writing tip 36 with a paint spray. In addition, the recording could be carried out on a film spread out on the concrete surface 39 or on an adhesive tape rolled out of the measuring part in the matrix or thermal printing process. The marking could also be done with the aid of adhesive dots from a supply roll in the measuring part. The marking could also contain additional information, for example about the depth and / or the diameter of the metal piece.

The metal detector according to FIG. 4 has a measuring part 41 and an evaluation part 42. The measuring part 41 comprises a displacement transducer 43, which supplies two signals J1 and J2 which are phase-shifted by 90 ° in order to distinguish the forward and the backward movement, as well as two coils 44, 45 which 3, an input unit 47 with a first key for switching the coils and a second key for establishing readiness for a measurement, and a display unit 48 with light-emitting diodes, lamps or LCDs.

The evaluation part 42 has a high-impedance oscillator 49 which is connected to a capacitor circuit 50 which forms a resonant circuit with the coil 44 or 45 which has just been activated. The output of the circuit 50 is connected via the series circuit of a rectifier circuit 51 and a low-pass filter 52 to the first input of a differential amplifier 53, the second input of which is supplied with the output signal of a digital-to-analog converter 54 used for automatic drift compensation. The output signal of the differential amplifier 53 is added to the data bus of a microprocessor 58 via the series connection of a multiplier 55, a non-linear amplifier 56 and an analog-digital converter 57. In addition, the evaluation part 42 comprises a forward-backward detector 59, which is acted upon by the signals J1 and J2, the pulse output of which is connected to the counter input of a counter 60, which together with a Read-write memory (RAM) 61, a read memory (ROM) 62 and an input and output circuit 63 is connected to the microprocessor 58, both the counter 60 and the circuit 63 having been won by the detector 59 ¬ Nnen forward-backward signal, which indicates the direction of movement. The circuit 63 supplies the digital signals for the digital-to-analog converter 54, for the display unit 48 and for a further display unit 64, and the calibration signal for the multiplier 55. The circuit 63, to which a further input unit 65 is connected, is connected to the input unit 47 via further connections.

4 works as follows:

The oscillating circuit formed by the capacitor circuit 50 and the coil 44 or 45 just connected is excited by the oscillator 49, the properties of the signal at the output of the circuit 50 being changed when metal is present in the vicinity of the coil. The change in amplitude is preferably evaluated. By switching from one coil to the other, additional information is obtained which allows not only the depth but also the diameter of a metal To determine the rod. The switchover can be carried out manually or automatically by the microprocessor 58 via the circuit 63 and the unit 47.

The output signal of the circuit 50 is fed through the described path to the signal input of the microprocessor 58, wherein the elements 53 to 56 can also be omitted if, for example, an analog-digital converter 57 with a high resolution of e.g. 12 bit is used, but it is expensive and / or slow. In contrast, the converters 54 and 57 in FIG. 4 would be provided for 8 bits. The microprocessor calculates the amplitude or another selected parameter of the input signal, stores the corresponding value and carries out all operations which have been described in connection with the method explained with reference to FIG. 2.

The main signal is multiplied by the multiplier 55 with a digital calibration signal supplied by the circuit 63, the value of the digital signal being a function of the selected rod diameter. The nonlinear amplifier 56, for example a logarithmizer, is provided in order to reduce the demands on the downstream converter 57 which result from the fact that The input signal of the same strongly depends on the depth of the reinforcing iron in the concrete. The memory 61 (RAM) serves to store the measured values and as working memory of the microprocessor. The memory 62 (ROM) contains the evaluation program and function tables. Of course, other more convenient memories can also be used.

With LED or LCD elements with switchable Hinter¬ backlight provided display unit 64 can be an alphanumeric display of the values of the bar depth or the overlap of the input or ^'calculated Stabdurch¬ diameter, the constants expected Messfehlerε, the Materialkon¬, zwiεchen the lateral Diεtanz the last two maxima or minima etc. enable. The input unit 65 has buttons and switches for selecting a desired type of use, for example for determining the rod depth for a given rod diameter, for triggering the automatic adjustment of the drift in order to emit a signal when there is no metal nearby simultaneous determination of the rod depth and the rod diameter, for entering parameters relating to the diameter, the material constant or the metal type, etc.

The unit 48 can have a plurality of lamps or light-emitting diodes, one for indicating that the displacement speed the measuring part or the probe has come close to the greatest permissible speed, another to indicate that there is no malfunction, and a third to indicate that a reinforcing iron was run over during a new measurement during the first direction of movement of the probe, and also to display the calculated position of the reinforcing bars during the movement in the second direction.

In a further embodiment of the invention, the measuring part 21 (FIG. 2) can have a single axis and a third point sliding on the surface, for example made of PTFE or sapphire.

Instead of the double coil, the auxiliary device can have a simple coil and means, for example similar to photo lenses, in order to move the coil into a second position which is raised by a defined amount over the concrete surface.

5, a scanning process can be carried out by moving the measuring part 9 without elements 6, 7, 8 (FIG. 1) in the forward or backward direction. The diagram (FIG. 5) shows the course of the signal strength S as a function of the scanning path X, For example, according to line 12 in FIG. 1, the metal parts sought being located below the signal maxima. If the measuring part passes over the points A, B, C,..., The electronics only recognizes a maximum (or a minimum) as such if the last stored largest signal value, for example S 1, around a certain amount S _M - - S. was undercut. In this position (point D), for example, a green LED 18 lights up, which thus indicates to the user of the device that a maximum (or minimum) has been exceeded. This is also the sign for changing the direction of movement. The user now moves the probe backwards over the points E, D, C, B. In the relatively small area DC, where the signal S is greater than S _R , another, for example, red light-emitting diode 18 lights up. In this area, therefore, lies a maximum (or minimum), the position of which can be determined more precisely by halving the illuminated area of the red light-emitting diode, for example by eye or by measuring. The same applies to the other maxima. Thus, the red LED lights up in the GHJK, KJ, JK, QP and PQ areas and the green LED in the KL, JH, KLM, QR, PN and QR areas. The marking device itself can also be used in combination with any metal detection device according to the prior art. The invention also includes the combination of measurement and evaluation part in one and the same unit.

Claims

Patent claims

1. Metal detector with a measuring part and an evaluating part (1), the measuring part generating a variable magnetic field and having a sensor (9) to change one of the metal parts (10, 10 ', 10 ") that are being sought Detecting magnetic field signal, characterized in that there is an auxiliary device (1, 9) for improving the accuracy in determining the position of the metal part sought, which device stores at least one physical quantity derived from the magnetic field signal and / or a double coil (26) in order to optionally generate at least two variable magnetic fields.

2. Metal detector according to claim 1, characterized ge indicates that the measuring part (21) slidably against the surface of the object being examined (28) and with a displacement measuring device (6, 7, 8; 24, 25) for detection. solution of the displacement path is provided on the surface.

3. Metal detector according to claim 1 or 2, characterized in that the measuring part (21) has rolling means (22, -22 ').

4. Metal detector according to one of claims 1 to 3, characterized in that a double coil with two concentric windings (32, 33) is present, and that the metal detector comprises switching devices (46) to selectively the windings (44, 45) individually or combined to connect to an evaluation part (42).

5. Metal detector according to one of claims 1 to 4, characterized in that the auxiliary device has means for moving a coil for generating the magnetic field into a second position, from which there is a change in the magnetic field lines.

6. Metal detector according to one of claims 2 to 5, characterized in that the Wegmessvorrich¬ device is based at least partially on the unwinding of a tensioned flexible traction means (8). 7. Metal detector according to one of claims 2 to 6, characterized in that the path measuring device

(6,

7, 8) for two-dimensional data acquisition and connected to a two-dimensional display device (2).

8. Metal detector according to one of claims 2 to 7, characterized in that the displacement measuring device is provided for at least partially electronic detection of the position of the measuring part on the surface, and that an electronic memory circuit (61, 62) is available for storing values of the sensor signal , in such a way that the stored signal values are assigned information on the position of the measuring part during the measurement.

9. Metal detector according to one of claims 1 to 8, characterized in that the auxiliary device has a memory which in each case stores a measured signal value derived from the magnetic field signal if it is greater or less than the last measured and stored signal value, and comprises a comparator circuit which compares the respective last measured signal value (SB1) with the last stored largest or smallest signal value (SM1) and emits a message signal if the difference between these two signal values values (SMI-SBl) each greater or less than a predetermined value, and that the signaling signal serves as a sign for changing the direction of movement.

10. Metal detector according to one of claims 1 to 9, characterized in that the auxiliary device has a marking device (34-37) in order to provide information about the position of an extreme value of the evaluated magnetic field signal by embossing a character on the surface of the examined object ( 39) to save.