The drawings show an exemplary embodiment of a sensor according to the invention that will be explained in detail in the description below. The figures, the description, and the claims contain numerous defining characteristics in combination. Those skilled in the art will also consider these defining characteristics individually and unite them in other meaningful combinations.
As an introduction, the discussion below will first briefly touch on the principle known from the prior art of compensating for the offset in inductive sensors through the use of three concentric sensor coils.
In order to illustrate the basic principle of a compensation sensor,
The two transmission coils 12 and 14 of the device according to
In the detectors of the prior art, these quantities must in the end be optimized so that in the absence of a metallic object, no flux or as little flux π as possible is excited in the reception coil 16 when current flows through the transmission coils 12 and 14. In the coil arrangement 10 according to
The sensor 110 according to the invention has a transmission coil 20 with a plurality of windings that are indicated only schematically in the depiction according to
But even in the absence of a metal object 24 in the vicinity of the coils 20 and 26, a relatively powerful signal (“dummy signal”) is produced, which can be sensed and measured in the reception coil. Metal objects change the reception signal, e.g. UE. The dummy signal UEwithout in the reception coil 26 is proportional to the current Is in the transmission coil and ideally, is phase-shifted by 90° in relation to it.
According to the invention, a special compensation transformer 28 is provided, whose primary side 30 is connected in series with the transmission coil 20. A compensation transformer of this kind generates a voltage UK that is likewise ideally phase-shifted by 90° and is proportional to the transmission current Is. If a suitable transmission ratio between the number of turns on the primary side 30 and secondary side 32 of the compensation transformer is selected, then by suitably connecting the secondary side windings of the transformer in series with the windings of the reception coil 26, it is possible to cancel out the resulting dummy signal.
To that end, in the exemplary embodiment in
Through suitable dimensioning of the numbers of turns of the transmission coil 22, reception coil 26, and compensation transformer 28, the voltage UG that can be sensed by the sensor according to the invention is (UG=UE+UK) in the ideal case and approaches zero in the absence of a metal object in the vicinity of the reception coil 26. Since a metal object changes the field induced in the reception coil 26, in the absence of such a metal object 24, the voltage UE induced in the reception coil 26 also changes. The compensation voltage UK on the secondary side 32 of the compensation transformer, however, remains unchanged with an appropriately shielded compensation capacitor. As a result, the voltage UG that can be detected in the sensor according to the invention indicates that a metal object 24 has been found.
A suitable transmission ratio of the primary and secondary windings of the compensation transformer is, in a first approximation, identical to the transmission ratio of the windings of the transmission coil in relation to the reception coil. Since the compensation transformer 28 is situated in the sensor 110 or an associated measuring device in such a way that it remains uninfluenced by metal objects, the output voltage UK of the transformer 28 also remains independent of the interference caused by the metal object 24 and is therefore constant. As a result, the full influence of the metal object 24 on the reception voltage UE is retained and is not also compensated away as is customary in sensors according to the prior art.
For example, the compensation transformer can be comprised of a ferrite toroidal core 40 and be provided with two correspondingly dimensioned windings 32 and 42. However, it is also possible to implement the compensation transformer in the form of a printed transformer in that the primary and secondary coils of such a transformer are applied, e.g. printed, directly onto a printed circuit board.
In addition to the sensor system schematically depicted in
The sensor according to the invention, together with the control and evaluation unit and a corresponding output unit, is integrated into a housing of a measuring device, in particular a compact hand-held measuring device. Such a measuring device can be manually moved with its housing or also by means of rollers situated on the housing over the surface of a wall, floor, or ceiling to be inspected.
The measuring device according to the invention also has a control area 58 with a number of control elements 60 that make it possible, for example, to switch the device on and off and to start a measuring procedure or calibration procedure as needed.
In the region below the control area 58, the measuring device according to
At its end 70 oriented away from the handle 64, the measuring device has an opening 72 passing through the housing. The opening 72 is situated concentrically in relation to at least the reception conductor loop system 34 of the sensor. In this way, the location of the opening 72 in the measuring device corresponds to the center of the locating sensor, thus also simultaneously showing the user of such a device the precise location of a potentially detected object. In addition, the measuring device also has marking lines 74 on its top side, which allow the user to locate the precise center of the opening 72 and thus the position of the enclosed object.
In addition to a purely inductive measuring device, the sensor according to the invention can also be used as an auxiliary sensor in measuring units that use other measuring methods. It is thus possible, for example, to also use the compensated, inductive sensor as an auxiliary diagnostic device in a radar locating device or an infrared locating device.
The sensor according to the invention and the measuring device according to the invention that is equipped with such device are not limited to the exemplary embodiments shown in the drawings.
In particular, the sensor according to the invention is not limited to the use of only one transmission coil and one reception conductor loop system. It can also be used in multiple systems, possibly through the use of a plurality of compensation transformers.
Number | Date | Country | Kind |
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102005002238.3 | Jan 2005 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP05/56093 | 11/21/2005 | WO | 00 | 4/9/2007 |