Inductive Sensor

Abstract

An inductive sensor insusceptible to external electromagnetic fields. The sensor coil is designed so as to have a first winding part and a second winding part connected thereto, the first winding part and the second winding part being wound in opposite directions. The first winding part is connected to a first coil terminal and the second winding part is connected to a second coil terminal.

Claims

1. An inductive sensor for monitoring the position of a traction cable of a cable car system, the sensor comprising a sensor coil having two coil terminals and a sensor evaluation unit which is connected to the two coil terminals, wherein the sensor coil is designed so as to have a first winding part and a second winding part connected thereto, the first winding part and the second winding part being wound in opposite directions and the first winding part being connected to a first coil terminal and the second winding part being connected to a second coil terminal, and the sensor coil is designed to be operatively connected to the traction cable and the sensor evaluation unit is designed to detect and evaluate a change in position of the traction cable relative to the sensor.

2. The inductive sensor according to claim 1, wherein the sensor coil is continuously wound in a figure of eight.

3. The inductive sensor according to claim 1, wherein a first single coil as the first winding part is connected in series with a second single coil as the second winding part.

4. The inductive sensor according to claim 3, wherein the first single coil and the second single coil are wound helically.

5. The inductive sensor according to claim 1, wherein the two winding parts are arranged one next to the other in one plane.

6. A cable car system comprising a traction cable and an inductive sensor according to claim 1 for monitoring the position of a the traction cable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the following, the present teaching will be explained in greater detail with reference to FIGS. 1 to 5, which show exemplary advantageous embodiments of the present teaching in a schematic and non-limiting manner. In the drawings:

[0013] FIG. 1 shows the operating principle of a contactless inductive sensor;

[0014] FIG. 2 shows a first embodiment of a sensor coil according to the present teaching;

[0015] FIG. 3 shows a further embodiment of a sensor coil according to the present teaching;

[0016] FIG. 4 shows a further embodiment of a sensor coil according to the present teaching; and

[0017] FIG. 5 shows the use of a sensor coil according to the present teaching for monitoring the position of a cable in a cable car system.

DETAILED DESCRIPTION

[0018] The principle of an inductive sensor for distance measurement is shown in FIG. 1. A sensor coil 3 generates an electromagnetic field which interacts with an electrically conductive object 4. This interaction can be detected and evaluated at the outlets 5 of the sensor coil 3 by a sensor evaluation unit 2, for example via the coil voltage u and/or the coil current i. In one embodiment as an eddy current sensor, an oscillator in the sensor evaluation unit 2 generates a high-frequency alternating voltage which is applied to the sensor coil 3 and generates a high-frequency alternating field. This high-frequency alternating field generates eddy currents in an object 4 in the region of influence of the sensor 1, which currents draw energy from the electromagnetic alternating field, thereby reducing the height of the oscillation amplitude of the oscillator voltage. This change in oscillation amplitude is evaluated by the sensor evaluation unit 2. If embodied as a proximity switch, the sensor 1 either supplies a high level or low level as an output signal A or the output signal A represents a measure of the distance between the sensor coil 3 and the object 4. In the latter case, the output signal A can be analog, for example an electrical voltage, or digital.

[0019] However, the principle according to which the inductive sensor 1 operates or how the sensor evaluation unit 2 is designed or how it is evaluated or in what way the output signal A is output is irrelevant to the present teaching.

[0020] The present teaching is based on a particular embodiment of the sensor coil 3. According to the present teaching, the sensor coil 3 is designed so as to have a first winding part 6a and a second winding part 6b connected thereto, the first winding part 6a and the second winding part 6b being wound in opposite directions. A first coil terminal 5a is connected to the first winding part 6a and a second coil terminal 5b is connected to the second winding part 6b. As a result of winding the two winding parts 6a, 6b in opposite directions, external electromagnetic fields induce opposite voltages in the two winding parts 6a, 6b, which voltages compensate for one another at least in part. In this way, a significantly lower overvoltage is produced by external electromagnetic fields at the coil terminals 5a, 5b. If the two winding parts 6a, 6b are identical except for the winding direction, the voltages induced therein substantially cancel one another out and there are no or only extremely low overvoltages at the coil terminals 5a, 5b. This applies at least to a homogeneous external electromagnetic field, but can usually be assumed for typical applications. However, even in the case of an inhomogeneous external field, the two induced voltages would largely compensate for one another.

[0021] The sensor coil 3 can be wound continuously or can also consist of two single coils connected in series.

[0022] In a first embodiment according to FIG. 2, the sensor coil 3 is continuously wound in a figure of eight. For the sake of simplicity, only two windings per winding part 6a, 6b are shown in FIG. 2, but the sensor coil 3 can of course also have more windings. As a result of the figure-of-eight-shaped winding, the two resulting winding parts 6a, 6b have opposite winding directions.

[0023] A similar result is obtained by first winding a coil, compressing the wound coil at one point and then rotating one of the resulting winding parts 6a by 180 with respect to the other winding part 6b. This likewise produces a continuously wound figure-of-eight-shaped sensor coil 3 which has two winding parts 6a, 6b wound in opposite directions.

[0024] A further embodiment is produced when two single coils 7a, 7b wound in opposite directions are connected in series. In this case, the two single coils 7a, 7b each form a winding part 6a, 6b in the sensor coil 3, as shown in FIG. 3.

[0025] In one particularly advantageous embodiment, the two single coils 7a, 7b forming the winding parts 6a, 6b are wound helically, as shown in FIG. 4. In this case, the windings of the winding parts 6a, 6b are preferably arranged in one plane. The winding parts 6a, 6b can in this case be wound as a single-layer helix or also as a multi-layer helix. In an embodiment of this kind, the sensor coil 3 can be particularly flat.

[0026] The advantage of the embodiment comprising single coils 7a, 7b connected in series compared to a continuously wound sensor coil 3 is that the voltage differences between adjacent windings of the sensor coil 3 are always small, and therefore no undesirable voltage breakdowns can occur which would destroy the sensor coil 3. In the case of a figure-of-eight-shaped embodiment, there may be large voltage differences between individual windings, in particular in the region of the crossing point of the individual windings, for which reason the risk of voltage breakdowns is higher in this case and therefore higher insulation measures have to be taken according to the circumstances.

[0027] In order to avoid the electromagnetic excitation fields generated by the winding parts 6a, 6b not completely or partially cancelling one another out, the two winding parts 6a, 6b are arranged one next to the other in one plane, as shown in the figures, and not one behind the other. This plane is also referred to as the active surface 8 (FIG. 1) of the sensor 1, from which surface the electromagnetic fields emanate. In this case, the object 4 is arranged opposite the active surface 8 of the sensor 1 in order to reach the region of influence of the electromagnetic fields.

[0028] The sensor 1 can also be used in safety-critical applications, and therefore the sensor 1 can also be designed to meet functional safety requirements (e.g. a safety requirement level in accordance with IEC 61508). For example, the sensor 1 could be designed so as to have a two-channel sensor evaluation unit 2, it also being possible to provide mutual checks on the channels. Of course, other or additional known measures for achieving functional safety are also conceivable.

[0029] One advantageous application of the inductive sensor 1 according to the present teaching is monitoring the position of a cable of a cable car system 10, as shown in FIG. 5. The cable car system 10 is only shown in part and as far as necessary in FIG. 5, since the basic structure of a cable car system in various embodiments is well known. In this case, the sensor 1 is arranged, for example, so as to be stationary in the region of a roller battery 11 on a cable car support comprising a number of cable rollers 12 and so as to be in contactless operative connection with a traction cable 13. Of course, the sensor 1 can also be arranged at any other point in the cable car system 10 in order to monitor the position of the traction cable 13. In operative connection in this case means, of course, that the traction cable 13, as the object 4, sufficiently influences the electromagnetic field of the sensor coil 3 of the sensor 1 that a change in position of the traction cable 13 relative to the sensor 1 can be detected and evaluated by the sensor evaluation unit 2. For this purpose, the traction cable 13 is arranged opposite the active surface 8 of the sensor 1. The output signal A from the sensor 1 is transmitted to a cable car control unit 20 and used in said unit to control the cable car system 10. The transmission can, of course, be wired or wireless. For example, depending on the output signal A, the conveying speed of the traction cable 13 can be changed, or the cable car system 10 can be stopped.