Magnetometer test arrangement and method

Manufacturing of magnetometer units (20′) employs a test socket (41) having a substantially rigid body (43) with a cavity (42) therein holding an untested unit (20) in a predetermined position (48) proximate electrical connection (50) thereto, wherein one or more magnetic field sources (281, 332, 333, 334, 335, 336) fixed in the body (43) provide known magnetic fields at the position (48) so that the response of each unit (20) is measured and compared to stored expected values. Based thereon, each unit (20) can be calibrated or trimmed by feeding corrective electrical signals back to the unit (20) through the test socket (41) until the actual and expected responses match or the unit (200) is discarded as uncorrectable. In a preferred embodiment, the magnetic field sources (281, 332, 333, 334, 335, 336) are substantially orthogonal coil pairs (332, 333, 334) arranged so that their centerlines (332-1, 333-1, 334-1) coincide at a common point (46) within the predetermined position (48). Because the test-socket (41) is especially rugged and compact, other functions (e.g., accelerometers) included in the unit (20) can also be easily tested and trimmed.

FIELD OF THE INVENTION

Embodiments of this invention relate generally to arrangements, sockets, and methods for testing and/or calibrating magnetometers, and to magnetometers that have been so tested and/or calibrated.

BACKGROUND OF THE INVENTION

A magnetometer is an electronic device for detecting the magnitude and/or orientation of a magnetic field. It is customary to test magnetometers in magnetic fields of known strength and orientation to determine their response and, in some cases adjust or “trim” the magnetometers to provide a predetermined output in response to known magnetic fields. This process is generally referred to as calibration and is a routine aspect of producing useful magnetometers. In some cases, other tests relating to, for example, acceleration, temperature, etc., may also be performed on magnetometers, especially where the magnetometers are intended for use in stressful environments.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description.

For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawings figures are not necessarily drawn to scale. For example, the dimensions of some of the elements or regions in the figures may be exaggerated relative to other elements or regions to help improve understanding of embodiments of the invention.

The terms “first,” “second,” “third,” “fourth” and the like in the description and the claims, if any, may be used for distinguishing between somewhat similar elements and not necessarily for describing a particular spatial arrangement or sequence or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation or construction in sequences, orientations and arrangements other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have” and any variations thereof, are intended to cover non-exclusive inclusions, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. As used herein the terms “substantial” and “substantially” mean sufficient to accomplish the stated purpose in a practical manner and that minor imperfections, if any, are not significant for the stated purpose.

The terms “trim” and “trimming” with reference to magnetometers are used herein to refer to altering the properties of a magnetometer so that when exposed to a stimulus (e.g., a magnetic field and/or acceleration and/or temperature and/or other physical environment) its output response to such stimulus more closely matches the expected or desired response from the magnetometer when exposed to such stimulus. This is also commonly called “calibrate” or “calibrating”, and the terms “trim” and “trimming” and “calibrate” or “calibrating” are used interchangeably herein.

FIGS. 1A,1B,1C, and1D show simplified top (FIG. 1A), side (FIG. 1B) and bottom (FIGS. 1C & 1D) views, respectively, of exemplary magnetometer20encased in body21and with electrical input-output (I/O) contacts or terminals22.FIGS. 1C and 1Dare non-limiting illustrations of different configurations of I/O contacts or terminals22. Any type of magnetic field sensor may be used as the active element within magnetometer20for detecting a magnetic field. Hall Effect semiconductor devices are well known magnetic field sensors but other types of sensors may also be used. Embodiments of the present invention do not depend upon the type of magnetic field sensor used within magnetometer20. In addition to including at least one magnetic field sensor of some type, it is common in the art that other types of electronic devices, particularly semiconductor devices and integrated circuits (ICs), may be incorporated within magnetometer20to provide a variety of further electronic functions (e.g., differential magnetic field detections, detection of acceleration, temperature, etc.), and especially to allow magnetometer20to be trimmed to suit particular functions.

Magnetometer20may be a unidirectional magnetometer, that is, adapted to respond substantially to magnetic fields in a particular direction with respect to magnetometer20, or may be a multidirectional magnetometer adapted to detect magnetic fields in multiple directions (e.g., in three dimensions), thereby providing information on the orientation of the magnetic field as well as its magnitude. For convenience of description, I/O contacts or terminals22are shown as being located on the lower surface of body21of magnetometer20, but may be located anywhere on magnetometer20and may be of any type. Non-limiting example of various contacts or terminals are solder bumps, surface contact pads, beam leads, externally extending leads, dual in-line leads, etc. Magnetometer20may include any or all of such variations as well as having other external and internal configurations. Magnetometer20may also be of a contactless type wherein communication to and from the magnetometer is handled wirelessly.

FIG. 2shows a schematic side view of testing arrangement24according to the prior art, wherein magnetometer20ofFIG. 1is located between a pair of electro-magnetic coils25providing substantially unidirectional magnetic field H passing through magnetometer20. Coil pair25shown in side view inFIG. 2and is generally circular in plan view.

FIG. 3shows a schematic side view of testing arrangement26according to the prior art, wherein magnetometer20is located between poles27of magnetic yoke28energized by current carrying coil29for providing substantially unidirectional magnetic field H passing through magnetometer20.

FIG. 4Ashows a simplified side view andFIG. 4Bshows a simplified top view of magnetometer20ofFIG. 1placed in three-dimensional (3-D) Helmholtz coil arrangement30for providing a test magnetic field of any orientation passing through magnetometer20, according to the prior art. To avoid cluttering the drawing, the magnetic field produced by the combination of orthogonally arranged coil pairs32,33and34is not indicated inFIGS. 4A and 4B(collectivelyFIG. 4). By varying the relative drive current provided to each of coil pairs32,33and34, the resulting magnetic field used to test magnetometer20can be oriented in any spatial direction with respect to magnetometer20.

While any of arrangements24,26,30can be used for generating magnetic fields for testing magnetometer20, in practical manufacturing such prior art arrangements have proved unwieldy. Among other things, the overall sizes of conventional magnetic field generating arrangements24,26,30ofFIGS. 2-4are bulky and ill suited to volume manufacture. For example, dimension37of 3-D Helmholtz coil arrangement30ofFIG. 4is typically several orders of magnitude larger than dimension23of magnetometer20. Stated another way, for example, the cubic volume occupied by 3-D Helmholtz coil arrangement30ofFIG. 4is typically 3×104to 3×108times the cubic volume of magnetometer23. Further, it is found that, despite care to render the magnetic fields produced by any of arrangements24,26,30substantially uniform where magnetometer20is located, the exact magnetic field to which magnetometer20is being exposed is sensitive to its exact position within arrangements24,26,30, and such problems tend to worsen as the overall size of arrangements24,26,30is reduced to facilitate their use in volume manufacturing. Further difficulties arise when magnetometer20contains other types of sensors as well as magnetic field sensors, for example, acceleration and/or temperature sensors. A problem with prior art testing arrangements such as are illustrated inFIGS. 2-4is that they are poorly adapted (e.g., too fragile) to permit concurrent testing of such other functions. Accordingly, there is an ongoing need for improved test arrangements and methods and magnetometers tested thereby, in which these and other difficulties associated with testing and calibrating or trimming magnetometers are reduced or eliminated. Among other things, the test sockets used to hold and energize a magnetometer and orient it with respect to a test magnetic field and the method of performing such test(s) are important aspects of the magnetometer manufacturing process and have great impact on the cost of manufacture and usefulness of a finished magnetometer product.

FIG. 5shows a simplified isometric view of arrangement40-1for testing the magnetometer ofFIG. 1, according to an embodiment of the invention, wherein test socket41-1for holding the magnetometer in predetermined relationship to Helmholtz coils analogous to those ofFIGS. 4A and 4Bis only partially completed. Test arrangement40-1comprises test socket41-1having body43-1formed from substantially non-magnetic material. Ceramic-filled PEEK (polyether ether ketone), polyimides such as Vespel® available from DuPont Inc. of Newark, Del., or polyamide-imides such as Torlon® available from Boedeker Corp. of Shiner, Tex., and liquid crystal polymer (LCP) are non-limiting examples of suitable materials for body43-1but other substantially non-magnetic materials can also be used provided that the resulting body is substantially rigid, so that the location(s) of magnetic field source(s) and the magnetometer under test are substantially constrained. Ceramic-filled PEEK (polyether ether ketone) is preferred for body43-1. Body43-1has therein cavity42-1for holding magnetometer20in a predetermined relationship to a magnetic field being generated within test socket41-1.

Body43-1has substantially orthogonal pairs of slots132,133,134in which coils analogous to coils32,33,34ofFIG. 4will be placed (e.g., see coil pairs332,333,334ofFIGS. 6-7and11-13), thereby forming a 3-D Helmholtz magnetic field generating arrangement in this embodiment. Substantially orthogonal slot pairs132,133,134are shown inFIG. 5, but the conductors making up the corresponding coil pairs (e.g., see coil pairs332,333,334ofFIGS. 6-7and11-13) are omitted fromFIG. 5in order to avoid unduly cluttering the drawing. It will be understood by those of skill in the art that substantially orthogonal slot pairs132,133,134are for the purpose of holding substantially orthogonal Helmholtz coil pairs analogous to coil pairs32,33,34ofFIG. 4, as are shown for example inFIGS. 6-7and11-13. Some or all of these coil pairs are energized during testing, calibration and or trimming to expose magnetometer20located within cavity42-1in body43-1of test socket41-1of test arrangement40-1to a desired magnetic field. Cavity42-1extends from upper surface44substantially into the center of text socket41-1, as can be seen more clearly inFIGS. 6-7and11-13. Reference number45indicates the approximate location of the cross-sections shown inFIGS. 6-7,11-13and elsewhere.

FIG. 6shows a simplified exploded cross-sectional view of test arrangement40-1comprising test socket41-1ofFIG. 5for holding magnetometer20ofFIG. 1in cavity42-1, illustrating how magnetometer20may be inserted and removed from cavity42-1of test socket41-1.FIG. 7shows a simplified cross-sectional view of test arrangement40-1comprising test socket41-1ofFIGS. 5-6after magnetometer20is placed within test socket41-1.FIGS. 6 and 7are discussed together. The cross-sectional views ofFIGS. 6 and 7are substantially vertical cross-sections through central portion45of test socket41-1ofFIG. 5. It is assumed inFIGS. 6-7(andFIGS. 8-14) that terminals22of magnetometer20are arranged as shown inFIG. 1D, but this is merely for convenience of illustration and not intended to be limiting. Persons of skill in the art will understand that the electrical connections (e.g. connections50-1through50-8) within socket41-1and sockets41-2through41-8are located so as to mate with whatever configuration of terminals22is present on magnetometer20.

Referring now toFIGS. 6-7, test socket41-1comprises body43-1of preferably non-magnetic material as previously discussed. Slot pairs132,133,134containing electromagnetic coils332,333,334respectively, are provided in body43-1. Slot pairs132,133,134preferably define a substantially round central armature around which coils pairs332,333,334are formed or placed, although such shape is not essential. Accordingly, coil pairs332,333,334are generally circular in plan view, although other plan view shapes may be used in other embodiments. Slot pairs132,133,134and corresponding coil pairs332,333,334are desirably substantially orthogonal to one another. For example, slot pair134and corresponding coil pair334have principal planes234that are substantially vertical inFIGS. 6-7. Slot pair133and corresponding coil pair333have principal planes233that are substantially horizontal inFIGS. 6-7. Slot pair132and corresponding coil pair332have principal planes232that are also generally vertical inFIGS. 6-7, but arranged so that principal planes232are oriented at substantially 90 degrees with respect to principal planes233and234.

In a preferred embodiment, centerline332-1passing between coil pair332, centerline333-1passing between coil pair333, and centerline334-1passing between coil pair334are substantially orthogonal and intersect at common point46-1. In a preferred embodiment, common point46-1is located within cavity42-1in zone or position48within cavity42-1substantially where magnetometer20will be located when it is placed in test socket41-1(e.g., seeFIG. 7). The outer perimeter of cavity42-1is conveniently shaped so as to substantially conform to body21of magnetometer20, or at least have guides related to the shape of body21so that magnetometer20fits snugly into zone or position48within cavity42-1where terminals22of magnetometer20can come into contact with electrical connection or test pins50-1of test socket41-1. It is desirable for manufacturing convenience that cavity42-1and/or body21of magnetometer20have some form of mutual alignment keys or shapes (not shown) to inhibit magnetometer20being inserted in cavity42-1in an incorrect azimuthal orientation. However, this is not essential. Connection or test pins50-1are preferably but not essentially of a spring-loaded variety (e.g., “pogo pins”) so that slight differences (e.g., in elevation) of terminals22of magnetometer20are accommodated. Any type of flexible connection (e.g., test pins)50-1may be used.

While cavities42-1through42-8(collectively cavities42) shown inFIGS. 5-14are shown as having substantially straight (e.g., vertical) sidewalls, this is merely for convenience of description and not intended to be limiting. The interior walls of cavities42may be sloped to facilitate easy entry therein of magnetometer20in the direction of arrow53, provided that the lower portion (e.g., zone or position48) within cavity42where magnetometer20comes to rest during testing (e.g., seeFIGS. 7-14) is sufficiently confining to provide the desired alignment of terminals22to connection or test pins50-1though50-8(collectively connection or test pins50) or other connection means (e.g., seeFIG. 13), and the desired alignment of magnetometer20to the magnetic field being created by yoke or coils281,332,333,334,335,336ofFIGS. 7-14.

Referring again toFIGS. 6-7, cap54-1having central extension or tang55-1and optional connection point57-1is desirably but not essentially provided. Cap54-1is adapted so that tang or extension55-1is inserted into cavity42-1following magnetometer20to ensure that magnetometer terminals22are firmly seated against connection or test pins50-1to provide electrical contact thereto. Coupling point57-1is desirably but not essentially included to facilitate coupling cap45-1with extension or tang55-1to, for example, a pick-and-place (P&P) machine to facilitate automatic insertion of magnetometer20and cap54-1into (and removal from) socket41-1. Cap54-1with extension or tang55-1also facilitates making sure that magnetometer20is reliably positioned in zone or position48proximate intersection point46-1where the most uniform portion of the magnetic field generated by, for example, coils332,333,334ofFIGS. 6-7is located. In a further embodiment, it is desirable that point47of magnetometer20indicating the location(s) within body21of the magnetic sensor(s) used for detecting the magnetic field passing through magnetometer20, is brought into close proximity with central magnetic field intersection point46-1of test socket41-1.

The foregoing testing arrangement has a number of significant advantages. For example, it is compact, having outer dimension56(seeFIG. 7) much less than outer dimension37of the prior art arrangements of, for exampleFIG. 4. For example, outer dimension56is generally less than about 16 times, conveniently less than about 10 times and preferably less than about 4.5 times dimension23of magnetometer20. Stated another way, where the cubic volume occupied by test socket41-1ofFIGS. 5-7(andFIGS. 8-14) is VTSand the cubic volume of magnetometer23is VMAG, then the ratio VTS/VMAGis usefully about VTS/VMAG≦2.8×104, more conveniently about VTS/VMAG≦1.25×104, and preferably about VTS/VMAG≦2×103. Compared to prior art magnetometer testing arrangements26,28,30such as those illustrated inFIGS. 2-4described earlier, where equivalent cubic volume ratios are between 3×104to 3×108, testing arrangement40-1employing socket41-1ofFIGS. 5-7can be volumetrically smaller than the prior art arrangements by at least one order of magnitude and typically by many orders of magnitude. This compactness is a great manufacturing convenience. Further, test socket41-1is relatively simple in design and construction and can be produced inexpensively to accommodate different body configurations of various magnetometers. In addition, it is simple to use and requires little training for high volume production operations. Still further, it substantially simplifies bringing each example or unit of magnetometer20being tested into substantially the same position with respect to the coils or other means for providing the applied magnetic field each time a unit is tested, calibrated and/or trimmed, so that errors associated with even small magnetic field non-uniformities are largely avoided. Yet another advantage of the foregoing testing arrangements is that they are extremely rugged. Magnetometer20is held firmly within rugged body43-1and magnetometer20can be subjected, for example, to large accelerations or temperature excursions without significant risk of damage and without magnetometer20having to be removed and placed in a different specially ruggedized test arrangement. Thus, when magnetometer20also contains, for example, acceleration and/or temperature and/or other sensors, magnetometer20can be tested for these functions as well as its magnetic field response without removing magnetometer20from test socket41-1of the type illustrated herein. Additionally the embodiments illustrated inFIGS. 5-7(and8-14) are: (i) adapted to function with existing pick & place (automated handling) equipment, (ii) use less power than the larger prior art arrangements ofFIGS. 2-4, (iii) can provide a uniform field of controllable magnitude and direction, (iv) unlike many prior art arrangements, are less prone to mutual interference when placed near each other in a compact manufacturing environment, and (v) are less effected or influenced by nearby ferro-magnetic metal structures commonly found in a manufacturing environment. These are significant advantages. Testing arrangements40-2through40-8with test sockets41-2through41-8ofFIGS. 8-14provide substantially similar benefits compared to the prior art arrangements.

FIG. 8shows a simplified cross-sectional view of test arrangement40-2analogous to that ofFIGS. 6-7, but according to a further embodiment of the invention wherein differently configured test socket41-2is provided using single electromagnetic coil335for generating the test magnetic field. Cap54-2with P&P coupling point57-2and extension or tang55-2adapted to move in directions53to hold magnetometer20in the desired position in cavity42-2are preferably included. Center point46-2of coil335is desirably located proximate magnetometer20and preferably proximate location47of the magnetic sensor(s) within magnetometer20. In the illustration ofFIG. 8, coil335is located at angle63-2in the x-y plane with respect to the principal face of magnetometer20, but persons of skill in the art will understand that coil335can have any desired angle with respect to magnetometer20and can be rotated around any of axes x, y or z to achieve the desired orientation with respect to magnetometer20. Coil335is desirably molded or otherwise solidly placed within body43-2of test socket41-2, but other means for fixing the relative position of coil335and magnetometer20may also be used. The advantages described earlier for arrangement40-1with test socket41-1relative to the prior art arrangements ofFIGS. 2-4also apply generally to arrangement40-2with test socket41-2.

FIG. 9shows a simplified cross-sectional view of test arrangement40-3analogous to that ofFIG. 8but according to a still further embodiment of the invention wherein differently configured test socket41-3is provided using a single pair of electromagnetic coils336analogous to coils25ofFIG. 2for providing the test magnetic field. Cap54-3with P&P coupling point57-3and extension or tang55-3adapted to move in directions53to hold magnetometer20in the desired position in cavity42-3during testing are preferably included. Center point46-3along common centerline336-1of coil pair336is desirably located proximate magnetometer20and preferably proximate location47of the magnetic sensor(s) within magnetometer20. In the illustration ofFIG. 9, centerline336-1of coil pair336is located at angle63-3in the x-y plane with respect to the principal face of magnetometer20, but persons of skill in the art will understand that coil pair336can have any desired angle with respect to magnetometer20and can be rotated around any of axes x, y or z to achieve the desired orientation with respect to magnetometer20. Coil pair336is desirably molded or otherwise solidly placed within body43-3of test socket41-3, but other means for fixing the relative position of coil pair336and magnetometer20may also be used. The advantages described earlier for arrangement40-1with test socket41-1relative to the prior art arrangements ofFIGS. 2-4also apply generally to arrangement40-3with test socket41-3.

FIG. 10shows a simplified cross-sectional view of test arrangement40-4analogous to that ofFIG. 8but according to a yet further embodiment of the invention wherein differently configured test socket41-4is provided using magnetic yoke or source281analogous to magnetic yoke28ofFIG. 3for providing the test magnetic field. Cap54-4with P&P coupling point57-4and extension or tang55-4adapted to move in directions53to hold magnetometer20in the desired position within cavity42-4are preferably included. Center point46-4between faces271of yoke281is desirably located proximate magnetometer20and preferably proximate location47of the magnetic sensor(s) within magnetometer20. In the illustration ofFIG. 10, yoke281is aligned approximately parallel to the principal face of magnetometer20, but persons of skill in the art will understand that yoke or source281can have any desired angle with respect to magnetometer20and can be rotated around any of axes x, y or z to achieve the desired orientation with respect to magnetometer20. Yoke or source281is desirably molded or otherwise solidly placed within body43-4of test socket41-4, but other means for fixing the relative position of yoke or source281and magnetometer20may also be used. In the illustration ofFIG. 10, yoke or source281has lower part283angled back behind the plane ofFIG. 10so that the central portion of lower part283and its energizing coil equivalent to coil29ofFIG. 3is located behind connection or test pins50-4. To avoid unduly cluttering the drawings, the energizing coil is not shown inFIG. 10. In an additional embodiment, the energizing coil may be replaced by a permanent magnet. The earlier described advantages of test arrangement40-1with test socket41-1relative to the prior art arrangements ofFIGS. 2-4also apply generally to arrangement40-4with test socket41-4.

FIG. 11shows a simplified cross-sectional view of test arrangement40-5analogous to that ofFIG. 7but according to a still yet further embodiment of the invention wherein somewhat differently configured test socket41-5is provided wherein electrical connection or test pins50-5to magnetometer20is made through cap54-5with P&P coupling point57-2and extension or tang55-5of test socket41-5, rather than through body43-5that is otherwise analogous to body43-1inFIGS. 5-7. In other respects test socket41-5ofFIG. 11is substantially similar to test socket41-1ofFIGS. 5-7, and the discussion ofFIGS. 5-7with respect to the test socket41-1is incorporated herein by reference. Test socket41-5has electrical connection or test pins50-5extending through cap54-5and extension or tang55-5into the interior of cavity42-5so as to connect with terminals22of magnetometer20. In the embodiment ofFIG. 11, magnetometer20is placed in cavity42-5with terminals22facing up, rather than facing down as illustrated inFIGS. 6-10. In other respects, it functions in the same way as previously described for test socket41-1. Persons of skill in the art will also understand that the “contacts in the cap” configuration illustrated inFIG. 11also applies to test sockets41-2through41-4and41-6through41-8illustrated elsewhere.

FIG. 12shows a simplified exploded cross-sectional view of test arrangement40-6analogous to that ofFIG. 6but according to a yet still further embodiment of the invention wherein somewhat differently configured test socket41-6is provided wherein magnetometer20is initially placed in extension or tang55-6of test socket cap54-6, and then combination544of cap54-6with magnetometer20held in tang or extension55-6is inserted into test socket cavity42-6of body43-6of test socket41-6. P&P coupling point57-6is desirably but not essentially included in cap54-6. When combination544is inserted into cavity42-6, terminals22of magnetometer20come into contact with connection or test pins50-6in substantially the same manner as already described for connection or test pins50-1of test socket45-1ofFIG. 7. Accordingly, the discussion of arrangement40-1with test socket41-5in connection withFIGS. 5-7applies generally to arrangement40-6with test socket41-6ofFIG. 12and is, therefore, incorporated herein by reference. Persons of skill in the art will also understand based on the discussion herein, that the “contacts in the cap” configuration illustrated inFIG. 11may be combined with the embodiment illustrated inFIG. 12by moving connection or test pins50-6from body43-6to extension or tang55-6of cap54-6. Either arrangement is useful.

FIG. 13shows a simplified cross-sectional view of test arrangement40-7analogous to that ofFIG. 7but according to a another embodiment of the invention wherein somewhat differently configured test socket41-7is provided, wherein electrical connection50-7to magnetometer20is made using wireless interface501. Test socket41-7comprises body43-7having cavity42-7therein in much the same configuration as in sockets41-1,41-6, etc. However, instead of having connections50-1through50-6traversing body43-7or cap54-7, electrical connection is made to magnetometer20by placing wireless interface501of connection50-7proximate magnetometer20, that is, close enough for wireless communication with magnetometer20. In this situation, magnetometer20also needs a wireless interface capability. Wireless interface technology is widely used, for example, in connection with radio frequency identification (RFID) tags, cell phones, and other two-way remotely addressable units (e.g., such as those employing the well known Bluetooth® protocol). In the example ofFIG. 13, wireless interface501is shown located in body43-7close to a compatible wireless interface unit within magnetometer20, but this is not essential and wireless interface501may also be located outside of body43-7or in other locations proximate magnetometer20where wireless communication with magnetometer20can occur. Magnetometer20is otherwise located substantially, proximate to centerline point46-1. External leads502allow signals to be coupled into wireless interface501for energizing and transferring information to and from magnetometer20. In yet other embodiments, wireless interface501and leads502may be placed in extension or tang55-7of cap54-7or wireless interface501and leads502may be located outside of body43-7. Any of such arrangements are useful.

FIG. 14shows a simplified cross-sectional view of testing arrangement40-8analogous to that ofFIGS. 5-13, but according to still another embodiment of the invention wherein differently configured test socket41-8is provided having therein one or more cams60for pressing terminals22of magnetometer20against electrical connections50-8within text socket41-8. One or more cams60are rotatably mounted on axles or shafts64within subsidiary cavities62, for example, in the sidewalls of principle cavity42-8. In the illustration ofFIG. 14, cam60L on the left inFIG. 14is shown rotated into the DOWN (pressing) position wherein it applies force on magnetometer20in the direction of connections or pins50-8so that terminals22of magnetometer20make good electrical contact with connections or pins50-8. Cam60R on the right inFIG. 14is shown rotated into the UP (retracted) position so that it does not protrude into magnetometer cavity42-8, thereby allowing magnetometer20to be freely inserted or removed from socket41-8. Persons of skill in the art will understand that when it is desired to insert or remove magnetometer20that both of cams60are rotated into the UP position and, preferably, that when it is desired to insure good electrical contact between magnetometer terminals22and test connections or pins50-8, both cams are desirably rotated into the DOWN position. Persons of skill in the art will also understand based on the description herein that one or more cams may be used and that cam(s)60may be rotated from outside of cavity42-8by, for example, fixing cam(s)60on axel(s) or shaft(s)64which extend through body43-8of socket41-8so as to be rotatable from outside of body43-8, thereby causing cam(s)60to rotate in response to twisting or rotating shafts or axels64.

Test arrangements40-1through40-8described above are collectively referred to as test arrangements40. Similarly: (1) test sockets41-1through41-8are collectively referred to as test sockets41; (2) test socket bodies43-1through43-8are collectively referred to as test socket bodies43; (3) test socket body cavities42-1through42-8are collectively referred to as test socket body cavities42; (4) test socket caps54-1through54-7are collectively referred to as test socket caps54; (5) test socket extensions or tangs55-1through55-7in the foregoing are collectively referred to as test socket extensions or tangs55; and (6) coupling or connection points57-1through57-7are referred to collectively as connection points57. It should also be understood with arrangements40and sockets41that socket caps54may be omitted and extensions or tangs55provided without caps54. Connection points55on extensions or tangs55may be attached to any other element (e.g., part of an automatic P & P handling machine—not shown) to facilitate insertion and removal of magnetometer20into and from socket41. Further, while extension or tang55is convenient for insuring that terminals22of magnetometer20are in reliable contact with external connection or test pins50, any other means of accomplishing this function may also be used. Non-limiting examples of alternative arrangements for insuring that magnetometer20is seated within zone48of socket40with terminals22touching electrical connection or test pins50are: (1) an inflatable bag(s) or chamber(s), for example mounted in the walls of cavity42, that expands within cavity42after magnetometer20is inserted in cavity42so as to press terminals22of magnetometer20against external electrical connection or test pins50, or (2) one or more levers or cams such as are illustrated inFIG. 14that may be stored in the walls of cavity42and that flip down as or after magnetometer20is inserted in cavity42to press terminals22of magnetometer20against electrical connection or test pins50, or any other element(s) that are retracted when magnetometer20is being inserted or removed from cavity42and that press on magnetometer20to push terminals22of magnetometer20against electrical connection or test pins50. Accordingly, extension or tang55, cam(s)60, and their equivalents may be more generally referred to as pressing elements55,60, and the term “pressing element” is intended to include any way of holding magnetometer20in zone48within test socket41during testing so that terminals22of magnetometer20and/or any wireless communication interface within magnetometer20are in electrical communication with connection or test pins50of test socket41.

Although coil pairs or coils332,333,334,335,336are shown in connection with arrangements40and sockets41, the current carrying leads needed to energize these and other coils have been omitted inFIGS. 5-14in order to avoid unduly cluttering the drawings and obscuring embodiments of the invention. However, such current carrying leads to the various coils used to generate the test magnetic fields are indicated schematically by link or bus408-1ofFIG. 15.

FIG. 15shows simplified schematic block diagram400of an electrical portion of test arrangements40illustrated inFIGS. 5-14, according to a still yet further embodiment of the invention. Electrical portion400comprises external input402coupled via bus or link402-1to controller404. Controller404is coupled by bus or link404-2to drivers408for supplying current to the various coils that produce magnetic fields Hx, Hy, Hz. Coil drivers408are coupled via bus or link408-1to the magnetic field producing coil or coils (e.g., yoke or coils281,332,333,334,335,336) within magnetometer test socket41, as have been illustrated for example inFIGS. 5-14. Within magnetometer test socket41is magnetometer20, various magnetic field sensor(s) and, in some cases other functions as well as calibration and trim circuitry associated with the magnetic sensor(s) and other functions (e.g., accelerometers, temperature gages, etc.). Controller404is also coupled by bus or link404-4to magnetometer response transceiver410which may also contain receivers for other functions as noted above and calibration, trim setting and other circuitry. Magnetometer response transceiver410receives responses from magnetometer20and sends them on to controller404and receives calibration, trimming and other instructions from controller404which it then passes on to magnetometer test socket41and magnetometer20. Magnetometer response receiver410and magnetometer test socket41are coupled by bus or link410-1. Controller404is also coupled by bus or link404-3to memory406. Memory406may contain both transient memory for use during various operations as well as permanent or semi-permanent memory for storing various program instructions and for longer term data storage. Controller404is coupled via bus or link404-5to external output412, as for example but not intended to be limiting, a display on which the status of magnetometer20and/or the various test functions being performed may be displayed as well as the test results. However, external output412is not limited merely to a display and may included means for recording and/or transmitting test result data and other information to other manufacturing operations, as well as to production control operations, customer service operations, data logging equipment or services, and other business functions.

FIGS. 16 and 17show simplified method600for testing, calibrating and/or trimming magnetometer20and other functions that may be included therein (e.g., accelerometers, etc.), using test arrangements40comprising test sockets41, for example, of the type illustrated inFIGS. 5-14and electrical portion400ofFIG. 14, according to additional embodiments of the invention. Referring now toFIG. 16, method600begins with START601and initial step602wherein magnetometer20is provided and installed in test socket41of any of the types illustrated inFIGS. 5-14and variations thereon. To reduce the clutter inFIGS. 16 and 17, the abbreviation “MAG.” is used for the word “magnetometer”. In step604, the magnetic field applied to magnetometer20in test socket41is set to zero. This may be accomplished for example, by setting the drive current supplied by coil driver408(seeFIG. 15) to yoke or coils281,332,333,334,335and/or336to zero, or if there is a significant background magnetic field in the test area that might affect the “zero H field” reading of the magnetic sensors within magnetometer20, then controller404can arrange to have coil driver408energize yoke or coils281,332,333,334,335and/or336to provide an equal and opposite field to the background field so that the net field at the location of magnetometer20is effectively zero. Either arrangement is useful depending upon the circumstances.

Continuing to refer toFIG. 16, in step606, in an exemplary embodiment, magnetometer20under test is queried by magnetometer response transceiver410to determine the response of magnetometer20to a “zero field” condition. In logical query step608of method600, controller404of electrical system400determines whether the response received from magnetometer20during the “zero field” test corresponds to the expected response stored in memory406. For example, if the output of magnetometer20corresponds to a “H≠0” output, then logical query608directs method along path609-1to loop limiting query step610wherein it is determined whether or not method600has made a corrective loop (e.g.,606,608,610,612,606, etc.) more than M times, where M is a number selected by, for example, the test engineer or other person supervising the test procedure. The purpose of query610is to interrupt the testing process if for some reason corrective loop606,608,610,612,606, etc., does not result in a unit with a correct zero field response. If the outcome of query610is “YES” indicating that the allowed number of loops has been reached then method600proceeds via path611-2to step630where magnetometer20under test is identified as a “FAILED” unit. Then method600proceeds along path631as further illustrated inFIG. 17.

If the outcome of loop limiting query610is “NO” indicating that the corrective loop limit M has not yet been reached, then method600advances via path611-1to step612, wherein the H=0 response of magnetometer is optionally trimmed, calibrated or otherwise adjusted (e.g., SET H=0 POINT). Method600then returns to step606where the response of magnetometer20to H=0 test condition is re-determined and in query608again compared with the expected response from memory406. This loop606,608,610,612,606, etc., is repeated until either loop limit M is exceeded (e.g., unit has FAILED) or the response of magnetometer20to an H=0 test condition corresponds to the expected response, which is indicated in query608as being “RESPONSE=0”, that is, corresponding to the expected output for H=0. This indicates that magnetometer20has been successfully calibrated for H=0 and/or has successfully passed the H=0 test or both. While the H=0 test, trim and/or calibration steps explained above are desirable, they are not essential and in still further embodiments they may omitted or an H=0 test accomplished in other ways, as for example but not intended to be limiting, by averaging the responses from H=+H1and H=−H1tests described below. Method600is intended to accommodate such variations.

Still referring toFIG. 16, method600then advances to step614wherein as directed by controller404, coil driver408provides predetermined currents to the various coils or coil pairs or yoke (e.g.,281,332,333,334,335, and/or336) of test socket41so as to expose magnetometer20to a predetermined magnetic field H of magnitude and direction H=+H1, keeping in mind that +H1may include components in any or all magnetic directions and magnitudes, e.g., +Hx, +Hy, +Hz. This is especially relevant in the arrangement illustrated by test sockets41-1and40-5through40-8wherein three substantially orthogonal coils332,333,334are provided, which when receiving currents Ix, Iy, Iz can provide any and all magnetic vectors +Hx, +Hy, +Hz, so that resulting magnetic field +H1has the desired direction and magnitude. In step616, the response of magnetometer20to magnetic field H=+H1is measured via transceiver410and controller404, and in step618temporarily stored in memory406for future use.

In step620of method600, as directed by controller404, coil driver408desirably provides predetermined currents to the various coils or coil pairs or yoke (e.g.,281,332,333,334,335, and/or336) of test socket41so as to expose magnetometer20to a predetermined magnetic field H of magnitude and direction H=−H2, keeping in mind that −H2may include components in any or all magnetic directions and magnitudes, e.g., −Hx, −Hy, −Hz. In a preferred embodiment, +H1and −H2desirably have different magnetic directions, as indicated by the + and − signs accompanying them, but this is not essential and H1and H2may have the same or different magnetic directions and/or magnitudes. Either arrangement is useful. In step624, the response of magnetometer20to magnetic field H=−H2is measured via transceiver410and controller404, and in step622temporarily stored in memory406for future use. In logical query626, controller404determines if the responses of magnetometer20to the +H1and −H2applied magnetic field tests received via transceiver410correspond to the expected responses stored in memory406, where “H1& H2RESPONSES=SPEC.” corresponds to a logical “YES” (i.e., meets the desired specification) and “H1& H2RESPONSES≠SPEC.” corresponds to a logical “NO”, that is, does not meet the desired specification. Persons of skill in the art will understand that “H1& H2RESPONSES≠SPEC.” also includes the situation where either of H1or H2responses fails to correspond to the stored specification value(s).

If the outcome of query626is “YES” then the unit is magnetically “GOOD” and method600advances via path627-1to step636inFIG. 17. If the outcome of query626is “NO”, indicating that the unit under test failed the test, then method600advances via path627-2to further logical query628wherein it is determined whether or not to merely reject the unit (e.g., follow path629-1to “IDENTIFY AS FAILED” step630and path631to “REMOVE MAG. FROM TEST SOCKET” step670ofFIG. 17), or to attempt to trim or calibrate the unit to provide the desired response when exposed to calibrating fields, e.g., +H1and/or −H2. Whether or not to reject or trim may be pre-determined by the test engineer or other person supervising the test procedure. If the outcome of query628is “TRIM” than as shown by path629-2method600advances to adjustment step632wherein using the stored responses received via transceiver410, controller404calculates an adjustment intended to have the magnetometer's response more closely match the specified response when subjected to magnetic fields H=+H1and/or −H2, and causes transceiver410to send such settings or changes in settings back to magnetometer20via link or bus410-1(seeFIG. 15). Method600desirably but not essentially proceeds to loop limiting step634, whose operation is similar to that of step610. If loop limit N is not exceeded, then method600proceeds via path635-2to step614already described and loop614,616,618,620,622,624,626,628,632,634is repeated until either loop limit N is exceeded (YES outcome) whereupon method600proceeds via path635-1to (“IDENTIFY AS FAILED”) step630and following, or if the outcome (“H1& H2RESPONSES=SPEC.”) of query626indicates that the magnetometer response matches the stored specifications and the unit passed the tests, then method600advances via path627-1to step636ofFIG. 17. Loop limiting step634and adjustment step632may be performed in either order. While method600illustrates the use of H=0 as well as +H and −H applied field tests, this is not essential and, depending upon the characteristics of magnetometer20being tested, one or more of H=0 and/or +H and/or −H tests may be performed or several of +H and/or −H tests may be performed with different magnetic directions and/or magnitudes, as determined by the test engineer or user. Method600is intended to accommodate such variations.

In a further embodiment, the magnetometer trimming operation is performed in two stages: (i) a coarse correction stage, and (ii) a fine correction stage. The coarse correction stage comprises: establishing a predetermined test magnetic field H (e.g., H=0, and/or H=+H1, and/or H=−H2, etc.) through magnetometer20, measuring the response of magnetometer20thereto and comparing it to the stored expected value, and when it does not substantially match the expected value, calculating a coarse correction parameter, sending the coarse correction parameter to the magnetometer to alter its response to the test magnetic field H, and re-measuring and comparing the re-measured value to the expected value. The fine correction stage comprises, calculating a fine correction parameter using the re-measured value, sending the fine correction parameter to magnetometer20, exposing the magnetometer to a predetermined test magnetic field H that may be the same or different than previously used, measuring the re-measured response of magnetometer20thereto and comparing it to the stored expected value. This two stage (coarse adjustment then fine adjustment) may be performed for any of the desired magnetometer parameters, including its response to non-magnetic stimuli as discussed later.

Referring now toFIG. 17, those units that have failed the above-described tests are proceeding via path631to “REMOVE MAG. FROM TEST SOCKET” step670and thence to END672. Those units that have passed the various magnetic tests described in connection withFIGS. 15-16proceed along path627-1fromFIG. 16to logical query step636ofFIG. 17, wherein it is determined whether or not other tests need to be performed on magnetometer20, in this example, query636corresponds to “ACCELERATION TEST NEEDED?”. It will be understood that “ACCELERATION” is merely exemplary and not limiting and that any other type of test may be substituted for the described acceleration tests. In general, such other tests may be described as subjecting the magnetometer to other energy sources besides the above-described magnetic field sources. If the outcome of query636is “NO” indicating that no other type of test is needed, then method600proceeds via path637-1to step670, where the device is removed from test socket41and, since it has passed prior tests, is sorted as a “GOOD” unit.

If the outcome of query636is YES indicating that other tests are needed, then method600proceeds via path637-2to step638where the environmental parameter being tested is set to an appropriate reference value. In the case of acceleration A, then A=0 is convenient. In the case of other functions or environmental variables that need to be tested, the condition to which magnetometer20will be exposed, is set to some convenient reference value determined by the magnetometer user or designer. In step640, the response of magnetometer20to the assigned environmental condition (e.g., A=0) is measured, e.g., via transceiver410, and reported to controller404and in query step642it is determined whether or not the response corresponds to the predicted value retrieved by controller404from memory406. In the case of A=0, the expected response from an accelerometer located within magnetometer20is also conveniently but not essentially zero, so that “RESPONSE=0” or equivalent indicates that the unit has passed this test (i.e., unit is, so far, GOOD) and “RESPONSE≠0” or equivalent indicates “FAIL”. A “FAIL” response can indicate that the unit is defective or that it has not yet been appropriately calibrated or trimmed. For a “FAIL” output of query642, method600proceeds via path643-1to loop limiting step644, similar in function to other loop limiting steps previously discussed. If the outcome of query644is “YES” that is, more than P loops have occurred (e.g., the unit could not be calibrated), then as indicated by path645-2method600proceeds to “IDENTIFY AS FAILED” step664and thence to “REMOVE MAG. FROM TEST SOCKET” step670and then to END672, where the unit can be sorted with those that have “FAILED” a test. If the outcome of query644is “NO” indicating the loop limit of P loops has not been exceeded, then as indicated by path645-1, method600proceeds to step646where the, e.g., accelerometer A=0 test condition response error is evaluated and a correction calculated by controller404and sent to magnetometer20via transceiver410. Method600then returns to SET A=0 CONDITION step638and the response of magnetometer20is measured again in step640and compared in query642to determine whether the adjustment has been successful. The loop638,640,642,644,646,638, etc. can be repeated until P is exceeded or the outcome of query642is “RESPONSE=0 (or whatever other reference point has been chosen) indicating that the unit has passed this test. While the A=0 test, trim and/or calibration steps explained above are desirable, they are not essential and in still further embodiments they may omitted or an A=0 test accomplished in other ways, as for example but not intended to be limiting, by averaging the responses from A=+A1and A=−A1tests described below. Method600is intended to accommodate such variations.

When an A=0 test has been performed and the outcome of query642is “RESPONSE=0” (or equivalent) indicating that the unit has passed this test (or the test has been omitted or otherwise accomplished), method600proceeds to steps648,650,652,654,656,658and query660, analogous to steps614,616,618,620,622,624and query626during magnetic testing of magnetometer, but in this case, magnetometer20is being subjected to various inputs relating to the function currently under test, e.g., acceleration. In the case of a built-in accelerometer function, acceleration A is set to, for example, various values A=+A1and/or −A2(see steps648,654), the responses of magnetometer20to such stimuli measured (steps650,656) and temporarily stored (steps652,658), then compared (step660) to the expected responses and a calibration or trim curve calculated and an adjusted calibration fed back (step666) to the accelerometer circuitry on board magnetometer20in generally the same manner as for the magnetic response calibration procedures described earlier. The loop648,650,652,654,656,658,660,662,666,668and along path669-1back to step648may be followed as long as loop limit Q has not been exceeded or until “A1& A2RESPONSES=SPEC.” (e.g., the unit is properly calibrated or trimmed) is obtained, and along path661-1to “REMOVE MAG. FROM TEST SOCKET” step670and then to END672where the unit may be classified as a GOOD unit. If loop limit Q in query668is exceeded, then it has not been possible to calibrate or trim the unit and method600proceeds as shown by path669-2to “IDENTIFY AS FAILED” step664, then to “REMOVE MAG. FROM TEST SOCKET” step670and then to END672where the unit may be classified as a “FAILED” unit. These tests may all be performed without removing magnetometer20from test socket41, although using more than one test socket is not precluded even though less economical. For convenience of description, a magnetometer that has not yet passed various tests may be identified herein as magnetometer20, and a unit that has passed various tests may be identified as magnetometer20′. While method600illustrates the use of, for example, A=0 as well as +A and/or −A tests, this is not essential and, depending upon the characteristics of magnetometer20being tested, one or more of A=0 and/or +A and/or −A tests (or equivalent parameter) may be performed or several of +A and/or −A tests may be performed with different directions and/or magnitudes, as determined by the test engineer or user. Accordingly, method600is intended to accommodate such variations.

According to a first embodiment, there is provided a test socket (41) for a magnetometer (20), comprising, a substantially rigid body (43) having therein a cavity (42) adapted to receive the magnetometer (20) in a predetermined position (48) within the body (43), one or more magnetic field sources (281,332,333,334,335,336) adapted to provide a magnetic field passing through the predetermined position (48), electrical connection (50) within or proximate the test socket (41) for temporary electrical coupling to the magnetometer (20) during testing, and a pressing element (55,60) adapted to fit into the cavity (42) to hold the magnetometer (20) in the predetermined position (48) electrically coupled to the electrical connection (50). According to a further embodiment, the one or more magnetic field sources (281,332,333,334,335,336) comprise one or more electrical coils (332,333,334,335,336) each having a centerline (e.g.,332-1,333-1,334-1,335-1,336-1) passing substantially through the predetermined position (48). According to a still further embodiment, the one or more magnetic field sources (281,332,333,334,335,336) comprise three substantially mutually orthogonal electrical coil pairs (332,333,334), wherein each coil pair (332,333,334) has a centerline (332-1,333-1,334-1) passing substantially through the predetermined position (48). According to a yet further embodiment, the centerlines (332-1,333-1,334-1) pass substantially through a common point (46) located within the predetermined position (48). According to a till yet further embodiment, the one or more magnetic field sources (281,332,333,334,335,336) are substantially fixedly held by the substantially rigid body (43) in predetermined relationship to the predetermined position (48). According to a yet still further embodiment, the magnetometer (20) is temporarily attached to the pressing element (55) when inserted into the test socket (41). According to another embodiment, the electrical connection (50) to the magnetometer (20) is held by the pressing element (55). According to a still another embodiment, magnetometer (20) has an exterior volume VMAGand the test socket (41) has an exterior volume VTSand a ratio VTS/VMAGis less than 2.8×104.

According to a second embodiment, there is provided a method (600) for manufacturing a magnetometer (20), comprising, installing the magnetometer (20) in a predetermined position (48) in a test socket (41), wherein the test socket comprises a substantially rigid body (43) with a cavity (42) therein adapted to receive the magnetometer (20) in the predetermined position (48) within the cavity (42), one or more magnetic field sources (281,332,333,334,335,336) fixedly held by the substantially rigid body (43) in predetermined relation to the predetermined position (48) and adapted to provide a magnetic field passing through the predetermined position (48), and electrical connection (50) adapted to provide electrically coupling to the magnetometer (20) during testing, holding the magnetometer (20) in the predetermined position (48) in cooperative contact or communication with the electrical connection (50) during testing, using the one or more magnetic field sources (281,332,333,334,335,336), creating a magnetic field H in the predetermined position (48) passing through the magnetometer (20), using the electrical connection (50), measuring a response of the magnetometer (20) to the magnetic field H, comparing the measured response to a stored expected value of the response to asses whether the magnetometer (20) provided an expected value of the response, and removing the magnetometer (20) from the test socket (41). According to a further embodiment, the holding step is performed using a pressing element (55,60) within the cavity (42). According to a still further embodiment, the pressing element (55,60) is retracted when the magnetometer (20) is being removed from the cavity (42). According to a yet further embodiment, if the magnetometer (20) did not provide an expected value, the method (600) further comprises, using the measured response to calculate a trimming or calibrating parameter intended to correct the measured response to more closely match the expected value, sending the trimming or calibrating parameter to the magnetometer (20), and repeating the creating, measuring, and comparing steps to assess a result thereof. According to a still yet further embodiment, the steps comprising calculating a trimming or calibrating parameter, sending it to the magnetometer (20), and comparing and assessing the results thereof, comprises at least, (i) a coarse trim or calibration and assessment operation, and (ii) a fine trim or calibration and assessment operation. According to a yet still further embodiment, the step of creating a magnetic field H in the predetermined position, comprises creating a magnetic field having at least two predetermined values. According to another embodiment, the method further comprises subjecting the magnetometer (20) in the same or a substantially similar test socket (41) to a test using a non-magnetic stimulus, measuring a response thereto and comparing it to an expected non-magnetic stimulus response value. According to a still another embodiment, the method still further comprises using the first response, obtaining and sending a first non-magnetic trimming or calibrating signal to the magnetometer (20) to alter its response to the non-magnetic stimulus, performing a further test using a non-magnetic stimulus, determining a further response thereto and comparing it to another expected non-magnetic stimulus response value. According to a yet another embodiment, the magnetometer (20) has an exterior volume VMAGand the test socket (41) has an exterior volume VTSand a ratio VTS/VMAGis less than 2.8×104.

According to a third embodiment, there is provided a method for manufacturing a magnetometer unit (20), comprising, inserting a magnetometer unit (20) in a test socket (41) having a substantially rigid body (43) with a cavity (42) therein for holding the unit (20) in a predetermined position (48) proximate electrical connection (50) thereto and one or more magnetic field sources (281,332,333,334,335,336) fixed in the body (43) to provide a known magnetic field H at the position (48), using the one or more magnetic field sources (281,332,333,334,335,336) fixed in the body (43), exposing the untested magnetometer unit (20) to the known magnetic field H, using the electrical connection (50), measuring a response of the magnetometer unit (20) to the magnetic field H, determining any difference between the measured response and a stored expected response to the magnetic field H, using such difference, calculating a trimming parameter adapted to alter the response of the magnetometer unit (20) to reduce the magnitude of the difference, performing a trimming operation by sending the trimming parameter to the magnetometer unit (20) using the electrical connection (50), and assessing the success of the trimming operation by repeating the exposing, measuring and determining steps. According to a further embodiment, the trimming operation comprises a coarse trimming and assessing operation, and thereafter repeating the exposing, measuring, determining and calculating steps to then perform a fine trimming and assessing operation. According to a still further embodiment, the method further comprises, in the same or a substantially similar test socket (41), exposing the magnetometer unit (20) to other energy sources, using the electrical connection (50), measuring a response of the magnetometer unit (20) to the other energy sources, determining any difference between the measured response and a stored expected response to the other energy sources, and if any substantial difference, performing a trimming operation to reduce the magnitude of the difference.