Method and apparatus employing two independent means for nulling an ambient magnetic field

Claim 2

Apparatus for nulling an ambient magnetic field in a volume including magnetically permeable material comprising, detection means for detection of said ambient magnetic field in said volume, compensation means for nulling the ambient field in said volume within a predetermined compensation range of value of the ambient magnetic field, the predetermined compensation range being considered as the range within which the compensation means is effective to null said ambient field, deperming means for nulling of at least a portion of the ambient field by inserting a magnetizing field independent of said compensation means into said volume, and controller means coupled to the detection means, compensation means and deperming means for maintaining constant the compensation means when the value of the ambient magnetic field detected by the detection means becomes greater than the predetermined compensation range, and for activating the deperming means to insert its magnetizing field into the volume to establish a new operating point about which the compensation means has a new but predetermined compensation range.

Claim 3

Apparatus for nulling the x, y, z orthogonal field components of an ambient magnetic field in a volume including magnetically permeable material comprising, detection means for detection of the x, y, z components of said ambient magnetic field in said volume, compensation means for nulling the x, y, z components of the ambient field in said volume within a pre-determined compensation range of values of the x, y, z field components of the ambient magnetic field, the predetermined compensation range being considered as the range within which the compensation means is operable at that time to effectively null said ambient field, deperming means for nulling of at least a portion of the ambient field by inserting a magnetizing field independent of said compensation means into said volume, and controller means coupled to the detection means, compensation means and deperming means for holding constant the compensation means when the value of the x, y, z components of the ambient magnetic field detected by the detection means exceeds the limits of the predetermined compensation range, and for activating the deperming means to insert its magnetizing field into the volume to establish a new x, y, z defined operating point about which the compensation means has a new but predetermined compensation range.

Claim 4

Apparatus for nulling the x, y, z orthogonal field components of an ambient magnetic field in a volume including magnetically permeable material comprising, detection means for detection of the x, y, z components of said ambient magnetic field in said volume, compensation means for nulling the x, y, z components of the ambient field in said volume within a pre-determined compensation range of values of the x, y, z field components of the ambient magnetic field, the predetermined compensation range being considered as the range within which the compensation means is operable at that time to effectively null said ambient field, deperming means for nulling of at least a portion of the ambient field by inserting a magnetizing field independent of said compensation means into said volume, and controller means coupled to the detection means, compensation means and deperming means for holding constant the compensation means when the value of the x, y, z components of the ambient magnetic field detected by the detection means exceeds the limits of the predetermined compensation range, and for activating the deperming means to insert its magnetizing field into the volume to establish a new x, y, z defined operating point about which the compensation means has a new but predetermined compensation range.

Claim 5

Apparatus in accordance with claim 2 wherein the detection means comprises a plurality of magnetic sensors.

Claim 6

Apparatus in accordance with either of claims 1 or 2 wherein a shadow mask cathode ray tube is contained within said volume.

Claim 7

Apparatus in accordance with claim 2 wherein said compensation means includes a plurality of electromagnetic coils.

Claim 8

Apparatus in accordance with claim 5 wherein said compensation means includes a series of electromagnet coils, each coil being similarly configured, but differently oriented with respect to each other and to said volume.

Claim 9

Apparatus in accordance with claim 6 wherein the detection means comprises a plurality of magnetic sensors, each associated with one of said coils, and wherein each coil is oriented the same with respect to the associated one of said sensors.

Claim 10

Apparatus in accordance with claim 6 wherein the compensation means comprises four coils.

Claim 11

Apparatus of claim 2 wherein the magnetically permeable material within the volume includes a shadow mask cathode ray tube and wherein said deperming means comprises an electromagnetic coil generating an initially strong underdamped magnetic field oriented along one of said x, y or z axes.

Claim 12

Apparatus in accordance with claim 8 wherein the deperming means comprises an electromagnet coil having a plurality of turns around an axis generally parallel to the electron beam axis of said cathode ray tube.

Claim 13

Apparatus in accordance with claim 2 wherein the controller means comprises a table means for expressing acceptable operating limits of the system, wherein for a given set of values of the x, y, z components of the ambient field establishing a selected operating point of the system, the table means expresses a selected predetermined compensation range within which the compensation means is considered to be operable at said selected operating point.

Claim 14

Apparatus in accordance with claim 11 wherein the controller means activates the compensation means when the present value of the x, y, z, components of the ambient magnetic field are within the selected predetermined compensation range at the selected operating point, and activates the deperming means when the present value of the x, y, z, components of the ambient magnetic field exceeds the limits of the selected predetermined compensation range at the selected operating point.

Claim 15

Apparatus for controlling the x, y, z orthogonal components of an ambient magnetic field detected within a given volume of a cathode ray tube device, the apparatus comprising a controller, a cathode ray tube display circuit coupled to said controller, a deperming means, coupled to the controller, for generating a magnetic field within the given volume, a detection and compensation means, coupled to the controller, for detection and resolution of sets of the x, y, z field components, a storage means, coupled to the controller, (a) for storing a collection of predetermined sets of ambient magnetic field x, y, z components which are deemed acceptable within the given volume of operation of the cathode ray tube device, and (b) for storing an acceptable range of deviation of the ambient field components for each such stored predetermined related set according to the characteristics of the cathode ray tube device, and, the controller employing a selected one of the sets of the x, y, z field components as a baseline set, and issuing a deperm command to the deperming means, and to the cathode ray tube display circuit to blank the cathode ray tube display during the deperm operation, when the detection and compensation means detects a set of the x, y, z field components which are outside of the acceptable range the deviation stored in the storage means related to the baseline set.

Claim 16

Apparatus for controlling the x, y, z orthogonal components of an ambient magnetic field detected within a given volume of a cathode ray tube device, the apparatus comprising a controller, a cathode ray tube display circuit coupled to said controller, a deperming means, coupled to the controller, for generating a magnetic field within the given volume, a detection and compensation means, coupled to the controller, for detection and resolution of sets of the x, y, z field components, a storage means, coupled to the controller, (a) for storing a collection of predetermined sets of ambient magnetic field x, y, z components which are deemed acceptable within the given volume of operation of the cathode ray tube device, and (b) for storing an acceptable range of deviation of the ambient field components for each such stored predetermined related set according to the characteristics of the cathode ray tube device, and, the controller employing a selected one of the sets of the x, y, z field components as a baseline set, and issuing a deperm command to the deperming means, and to the cathode ray tube display circuit to blank the cathode ray tube display during the deperm operation, when the detection and compensation means detects a set of the x, y, z field components which are outside of the acceptable range the deviation stored in the storage means related to the baseline set.

Claim 21

A method in accordance with claim 15 wherein a shadow mask cathode ray tube in included within the volume, said cathode ray tube having its electron beam axis generally aligned with said z component, and wherein said second magnetic field is oriented along said z component.

Claim 22

A method in accordance with claim 16 wherein said second magnetic field is generated by an electromagnet coil having a plurality of turns around an axis generally parallel to the electron beam axis of said cathode ray tube.

Claim 23

A method in accordance with claim 15 wherein the step of determining whether the ambient field exceeds the limits of the compensation range comprises, establishing a look up table for expressing acceptable operating limits of the system, and wherein for a given set of values of the x, y, z components of the ambient field defining a selected operating point of the system, said determination is made by looking up in the table the selected predetermined compensation range within which the first magnetic field can be operable at said selected operating point.

Claim 24

A method in accordance with claim 15 wherein the step of determining whether the ambient field exceeds the limits of the compensation range comprises, establishing a look up table for expressing acceptable operating limits of the system, such that for a given set of x, y, z values of said ambient field defining a selected operating point, said table expresses the value of said predetermined compensation range, and looking up said predetermined compensation range in said table for the detected ambient field value to determine whether said value exceeds the limits of said compensation range.

Claim 25

A method in accordance with claim 18 wherein said look up table comprises a storage means, for storing a collection of predetermined sets of ambient magnetic field x, y, z components which are deemed acceptable within the given volume of operation of the CRT device, and for storing an acceptable range of deviation of the ambient field components for each such stored predetermined related set according to the characteristics oft he cathode ray tube device, and, wherein said determination is made by employing a selected one of the sets of the x, y, z field components as a baseline set, and determining that the detected value of said ambient field at any given time exceeds the limits of the compensation range when the detected value represents a set of the x, y, z field components which exceeds the limits of the acceptable range of deviation stored in the storage means related to that baseline set.