Precision measurement of magnetic characteristics of an article with nullification of external magnetic fields

Claim 1

A method for characterizing the magnetic field of a device under test, comprising: nullifying the ambient magnetic field in a test environment area, said nullifying comprising: (a) measuring and retrievably storing three orthogonal components of the ambient magnetic field strength in said test environment area, (b) computing in processor means a requisite current to be provided in respective orthonal Helmholtz coils for nullifying the corresponding orthogonal magnetic field strength components, and (c) maintaining a constant current equal to said requisite current in each respective Helmholtz coil whereby to nullify said ambient field so as to refrain from changing said constant current while performing subsequent sensing steps: placing the device under test in the test environment area; rotating the device under test in the test environment area at least nearly through a complete circle; sensing and recording the magnetic field at a sensor location which is along the circumference of rotation of the device as a function of the angle of rotation of the device; re-orienting the device to a successive one of a set of predetermined orientations and repeating said rotating and sensing steps, so as to obtain a profile of the magnetic field at said sensor location as a function of the angle of rotation of the device for each one of said set of predetermined orientations of said device under test; characterizing the magnetic field of said device from the magnetic field profiles obtained for said set of orientations.

Claim 2

A method for characterizing the magnetic field of a device under test, comprising: nullifying the ambient magnetic field in a test environment area, said nullifying comprising: (a) measuring and retrievably storing three orthogonal components of the ambient magnetic field strength in said test environment area, (b) computing in processor means a requisite current to be provided in respective orthonal Helmholtz coils for nullifying the corresponding orthogonal magnetic field strength components, and (c) maintaining a constant current equal to said requisite current in each respective Helmholtz coil whereby to nullify said ambient field so as to refrain from changing said constant current while performing subsequent sensing steps: placing the device under test in the test environment area; rotating the device under test in the test environment area at least nearly through a complete circle; sensing and recording the magnetic field at a sensor location which is along the circumference of rotation of the device as a function of the angle of rotation of the device; re-orienting the device to a successive one of a set of predetermined orientations and repeating said rotating and sensing steps, so as to obtain a profile of the magnetic field at said sensor location as a function of the angle of rotation of the device for each one of said set of predetermined orientations of said device under test; characterizing the magnetic field of said device from the magnetic field profiles obtained for said set of orientations.

Claim 8

A method of assembling an exploratory vehicle having an on-board magnetic field sensor whereby individual components of said vehicle introduce virtually no magnetic fields to said on-board magnetic field sensor, said method comprising the following steps carried out for each one of said components prior to their inclusion in said vehicle: nullifying the ambient magnetic field in a test environment area, said nullifying comprising: (a) measuring and retrievably storing three orthogonal components of the ambient magnetic field strength in said test environment area, (b) computing in processor means a requisite current to be provided in respective orthogonal Helmholtz coils for nullifying the corresponding orthogonal magnetic field strength components, and (c) maintaining a constant current equal to said requisite current in each respective Helmholtz coil whereby to nullify said ambient field; placing the one component in the test environment area; rotating the one component in the test environment area at least nearly through a complete circle; sensing and recording the magnetic field at a sensor location which is along the circumference of rotation of the one component as a function of the angle of rotation of the one component; re-orienting the one component to a successive one of a set of predetermined orientations and repeating said rotating and sensing steps, so as to obtain a profile of the magnetic field at said sensor location as a function of the angle of rotation of the one component for each one of said set of predetermined orientations of said one component; characterizing the magnetic field of said one component from the magnetic field profiles obtained for said set of orientations; determining from said characterizing step the field strength and particular orientation of a permanent magnet to be attached to said one component so as to nullify the magnetic field of said one component; and attaching a permanent magnet having said field strength to said one component in accordance with said particular orientation, whereby to produce a component for inclusion in said vehicle which at least nearly does not introduce a magnetic field to said on-board sensor.

Claim 9

A method of assembling an exploratory vehicle having an on-board magnetic field sensor whereby individual components of said vehicle introduce virtually no magnetic fields to said on-board magnetic field sensor, said method comprising the following steps carried out for each one of said components prior to their inclusion in said vehicle: nullifying the ambient magnetic field in a test environment area, said nullifying comprising: (a) measuring and retrievably storing three orthogonal components of the ambient magnetic field strength in said test environment area, (b) computing in processor means a requisite current to be provided in respective orthogonal Helmholtz coils for nullifying the corresponding orthogonal magnetic field strength components, and (c) maintaining a constant current equal to said requisite current in each respective Helmholtz coil whereby to nullify said ambient field; placing the one component in the test environment area; rotating the one component in the test environment area at least nearly through a complete circle; sensing and recording the magnetic field at a sensor location which is along the circumference of rotation of the one component as a function of the angle of rotation of the one component; re-orienting the one component to a successive one of a set of predetermined orientations and repeating said rotating and sensing steps, so as to obtain a profile of the magnetic field at said sensor location as a function of the angle of rotation of the one component for each one of said set of predetermined orientations of said one component; characterizing the magnetic field of said one component from the magnetic field profiles obtained for said set of orientations; determining from said characterizing step the field strength and particular orientation of a permanent magnet to be attached to said one component so as to nullify the magnetic field of said one component; and attaching a permanent magnet having said field strength to said one component in accordance with said particular orientation, whereby to produce a component for inclusion in said vehicle which at least nearly does not introduce a magnetic field to said on-board sensor.