Sensor for a metal detector.

The invention relates to a probe for a metal detector comprising a plate-shaped housing, with a device disposed in the transmitting coil and at least two arranged therein, electrically connected in series and lying in the same plane as the transmitting coil substantially receiver coil.

Metal detectors with which the ground or other non-metallic media are studied, essentially consist of a disk- or ring-shaped probe that receives one or more search coils, and a device electronics with power supply, which generates audible or visual display signals in presence of metal. The search coil consists of transmitter and receiver coils. These may also be combined to form a coil.

The operation of such devices is that of the probe an alternating electromagnetic field or short pulses are sent out, which induce eddy currents in the metal search objects. These eddy currents cause Sekundärfe.ld, which reacts to a magnetic echo or locating signal to the probe. Depending on the circuit principle, the probe may include one or more search coils, carry out different functions.

Simple metal detectors are designed as so-called relative diameter. They only indicate the relative change in conductivity of the medium being studied. Their main disadvantage is that you scan medium, such as highly mineralized soil, magnetic pavements or salt water may cause significant interference.

Here help so-called difference meter. Ground magnetic effects, disturbing conductivity and alternating field influences by a differential measurement, which takes place in the probe, are hidden within wide limits. The principle is that the effect lying in the field of a transmitter coil receiver coils are electrically connected to each other and are arranged in the space symmetrically with respect to the search coil. This transmitter and receiver side processes are decoupled.

If the interfering background homogeneous per se, is the electrical difference between the receiver coils zero. There is no noise. The effect of interfering alternating fields, such as those produced for example from power lines distinguishes itself in the opposite direction-connected receiver coils.

The principle of differential measurement is already well known among metal detectors; so for example, mine detectors American or French style, in which four against each connected receiver coils are arranged around a transmitter coil. Such a probe is shown in Fig. 1 schematically. It is constructed as follows:<ul><li>On the transmitter coil are decoupled by their geometric arrangement of receiver coils_, connected dieelektrisch so that the currents induced in them residual stresses cancel each other out. The coils are in a plate-like body of rectangular shape. The base plate takes the coil into a depression. The four receiver coils are located in recesses of the housing cover.</li></ul>

This embodiment has a large area weight and a high Ge. A so-built probe is not only cumbersome, but very exposed by the large surface thermal influences. This causes electrical instability. This disadvantage trying to counter by pocket-like sheaths of heat insulating material. The preparation of such a probe is relatively costly, cumbersome and therefore expensive. In practical use, the so running probe not only weight penalties, high water resistance with fast searches, such as in shallow pools, but also a small localization sharpness in locating the probe edge (Search with vertically tilted probe).

From this prior art, starting the present invention the task has made to overcome these disadvantages of a differential diameter and to provide an arrangement that is lightweight and portable, in the exact location and cost-effectively. The solution to this problem is given by the invention in a surprisingly simple manner in that the receiver coils are within the transmitter coil. In this arrangement, predetermined by the size DERS forming coil volume of the housing is not increased and optimally used. In contrast to the known differential diameters neither the cross-section or the height of the housing can be increased. Thus the housing remain weight and surface low. The housing and hence also the coils are heated by solar radiation only slightly. Also, the aforementioned water resistance remains low. The localization sharpness.

Suitably, the housing is divided by at least one web into several sections and the Empängerspulen are arranged in these. Here, the web can extend symmetrically through the center of the housing or at a distance from and pass through parallel to the center line of the housing therethrough. Thus, the receiver coils are different in size and get different inductors. This can be balanced electrically.

In general, the housing is divided by a web into two sections. This means that two receiver coils are arranged in a transmitter coil. However, the housing may be 90 ° intersecting webs be divided into four sections or three under 120 ° intersecting webs into three sections by two. In these cases, four or three receiver coils are positioned within a transmitter coil.

Advantageously the web or the webs in cross-section U-profile, the web of the U-section resting on the bottom of the housing or is formed integrally therewith, while the flanges upstanding and the coils are laid around the flanges.

Here, a web extends along the circumference of the housing, while the flanges of the or of extending through the housing ribs in the inner flange of the running along the circumference of the web pass over, and the coils are inserted in the space enclosed by the flanges of all the webs wells. Thus, the individual windings of the coil to be held securely.

Normally, the housing has a circular shape. However, it can also have square shape or any other shape.

In the normal case, the receiver coils are within the transmitter coil. However, the outer coil can be used as the receiver coil and the inner coil may be connected as a transmitter coil.

For the expert it is also understood that symmetrical coil in the probe housing are not absolutely necessary, since the compensation effect of the various search coils electrically even with different sizes, ie by companies

different number of windings can be brought about. The essential advantage of the invention lies not only in the ease of manufacture, but also in the close coupling of the coils, whereby a high detection sensitivity is achieved. A sharp locate small metal objects with the probe edge is possible. The so performed probe is light in weight and has in the underwater search only a slight resistance to movement. Due to the small surface of the thermal effect is only slight. The symmetrical design of the probe and coil high electrical stability is achieved even at different temperature exposure. The production of various housing is easy as the plastic injection mold for the different webs can be made interchangeable.

It was stated that the housing can be divided by three webs in three circular-sector-shaped sections and in each section a receiver coil may be placed. One of these coils can also be switched as a transmitter coil, the other two coils are connected against each other for a differential measurement and zero compensation.

Using the example of embodiments shown in the drawing, the invention will now be further described. In the drawings:<ul><li>Fig. 1 is a schematic plan view of a Differential measurer according to the state of the art,</li><li>FIG. 2 is a plan view of an inventively constituted body with the cover removed with a centrally extending through the housing web,</li><li>Fig. 3 is a plan view of the inserted into this housing the transmitting and the two receiving coils inserted,</li><li>Fig. 4 is a plan view of an inventively shaped housing with two by this passing and intersecting at 90 ° Stegen,</li><li>Fig. 5 is a schematic plan view of the inserted into the housing according to Fig. 4 transmission and the four loaded receiver coils,</li><li>Fig. 6 is a plan view of a three webs divided into three circular-sector-shaped sections housing with the cover removed, and</li><li>Fig. 7 is a schematic plan view of the inserted into the housing of FIG. 6 coils.</li></ul>

Fig. 1 shows the housing 12 of the known difference meter. The transmitter coil 14 is located in the housing 12, four receiver coils 16, 18, 20 and 22 above the transmitter coil 14 are located to lie in recesses or depressions in the housing cover.

FIG. 2 shows the housing 12 of an inventive probe. A jetty with upstanding flanges 24 extending along the center line through the housing 12. Another web with upstanding flanges 24 running along and parallel to the circumference of the housing. The flanges 24 into each other and connect wells 26 a. As shown in FIG. 3 is the transmitter coil 14 in the circumferentially extending recess of the housing 26. The two receiver coils 16 and 18 are in the other two D-shaped depressions 26. This gives them self and D form.

In the embodiment shown in FIG. 4, two lost below 90 ° intersecting webs with flanges 24 through the housing. As with the embodiment of FIG. 2, a further web with flanges 24 extending along and parallel to the periphery of the housing. The upstanding flanges 24 of the webs merge into one another. This gives rise to four circular sector shaped troughs 26. As shown in Fig. 5 is the transmitter coil 14 in the extending at the periphery of the housing recess 26. The four receiver coils 16, 18, ​​20 and 22 lie in the four sector-shaped troughs 26th

Figures 6 and 7 show the same image on a three webs divided into three sections housing 12. As noted, three receiver coils 16, 18, 20 may lie in a transmitter coil 14 here. Similarly, the wound in a circular form transmitter coil 14 can be omitted. One of lying in a circle sector coils is then switched to a transmitter coil.

In all embodiments, the coils are potted in the housing with a synthetic resin.