According to the present invention there is provided apparatus for determining orientation relative to a magnetic field in a three dimensional space comprising means for detecting a magnetic field in each of three mutually substantially orthogonal directions operative to produce an output indicative of detected magnetic field in each direction, and means for processing operative to process the output to determine the orientation of the means for detecting relative to the detected magnetic field.

Preferably a means for concentrating magnetic field is associated with the means for detecting. The means for concentrating is preferably arranged to concentrate magnetic field flowing in one or more directions and preferably comprises a rod of material of high magnetic permeability, such as ferrite. The means for detecting may be sandwiched between two such rods arranged end to end. Alternatively the means for detecting could be embedded in such a rod.

Preferably the means for detecting comprises three magnetic field detectors each arranged to detect magnetic field in one of three mutually substantially orthogonal directions. Each detector may be associated with a respective means for concentrating magnetic field.

One or more of the detectors may comprise a Hall Effect device. Other suitable detectors or combinations of detectors may, however, be used, including but not limited to fluxgate, wound core inductive, magneto-resistive or like detectors. Commercial

magnetic field gradient sensors in the form of an integrated circuit could also be used as the detector. Different types of detectors may be used to detect the field in different directions. In one embodiment three separate Hall Effect devices are employed each sandwiched between two rods of material of high magnetic permeability. In another embodiment a so-called multi dimensional Hall Effect device is employed capable of detecting magnetic field in at least two mutually substantially orthogonal directions. Such a Hall Effect device may be disposed in a means for concentrating a magnetic field arranged to concentrate magnetic field emanating from at least two mutually substantially orthogonal directions, for example by being sandwiched between two or more portions of such a means.

The means for processing preferably comprises a microprocessor.

Preferably there is also provided an output means operative to convey information to a user and an input means operative to enable a user to input information into the processor.

The output of the means for detecting a magnetic field preferably comprises three signals, each signal being indicative of the detected magnetic field strength in one of the three directions.

In order that the invention may be more clearly understood embodiments thereof will now be described by way of example with reference to the accompanying drawings of which : Figure 1 shows an exploded perspective view of a Hall Effect device and ferrite rod assembly used in an embodiment of the present invention; Figure 2 shows an arrangement of three of the type of assembly illustrated in Figure

1 ; Figure 3 shows part of an alternative embodiment of the present invention; and Figure 4 shows a schematic representation of an electronic circuit suitable for use with either of the arrangements illustrated in Figures 2 or 3.

Referring to Figure 1 a Hall Effect chip 1 is shown disposed between respective ends of two substantially cylindrical ferrite rods 2. The ferrite rods serve to concentrate an incident magnetic field on the Hall chip 1. The Hall chip includes a number of electrical connections 3, two for conducting a drive current to the chip and two to enable the Hall voltage generated by the chip to be measured.

Figure 2 shows an arrangement of Hall Effect chip and ferrite rod assemblies ofthe type shown in Figure 1. Three such assemblies are arranged with the long axis of the ferrite rods of each assembly extending in three respective mutually orthogonal directions.

With this arrangement each Hall device will measure the magnitude of incident magnetic field in the direction in which its associated ferrite rod 2 extends.

Figure 3 shows an alternative arrangement to that shown in Figure 2. This arrangement comprises a body 6 of ferrite material having six arms radiating from a central point the arms being arranged into three pairs, the arms of each pair extending along a common axis, the three axes along which each pair extend being mutually orthogonal.

Three Hall Effect chips (not shown) are located in the body and arranged to measure magnetic field strength along each of the three axes respectively. In an alternative arrangement a single multi-dimensional Hall chip is disposed in the body and operative to measure magnetic field in each of the three directions.

The arrangements described with reference to Figures 2 and 3 are operative, when

the Hall chips are connected to appropriate drive and detecting circuitry which is well known and understood, to produce three electrical outputs indicative of the strength of magnetic field detected in each of three mutually orthogonal directions. In each arrangement this output is conducted to a processing means, an embodiment of which is illustrated schematically in Figure 4 along with three Hall devices.

Referring to Figure 4 three Hall Effect devices 2 are arranged to measure magnetic field strength in each of three mutually orthogonal directions which, for convenience, shall be referred to as X, Y and Z directions. The output of each Hall Effect device 2 is conducted to an amplifier and then to an analog to digital converter and multiplexer 4 which converts the amplified output of the Hall Effect devices 2 to a digital signal which is transmitted to a digital microprocessor 5. The microprocessor is connected to an output means 6 and an input means 7.

The microprocessor 5 is operative to determine the orientation of the three Hall Effect devices 2 in three dimensions with respect to a magnetic field.

The X, Y and Z directions define three orthogonal planes, the X, Y plane, the X, Z plane and the Y, Z plane. By comparing the output of any two of the Hall Effect devices it is possible by simple geometry to calculate the angle between the direction of a measured magnetic field and one of the axes lying within a plane, in that plane. By repeating this process for two of the defined planes it is possible to calculate the direction of detected magnetic field in three dimensions with respect to the detector arrangement.

The apparatus is useful, for example, for determining orientation relative to the earth's magnetic field. Such information is usual for navigation and positioning of objects.

The apparatus may be arranged so that a user may select a particular direction as a

reference direction, and then operate to indicate deviation from that direction. A direction may be selected by orienting the means for detecting magnetic field in a chosen direction relative to a magnetic field, such as the earth's magnetic field, and making an input to the processor. The processor may then produce an output when the orientation of the means for detecting magnetic field relative to the magnetic field deviates from the selected orientation. The output may indicate the way in which the orientation of the means for detecting magnetic field has deviated from the selected orientation.

The above embodiments are described by way of example only. Many variations are possible without departing from the invention.