CA1177891A - Magnetic sensors having misalignment compensating means - Google Patents
Magnetic sensors having misalignment compensating meansInfo
- Publication number
- CA1177891A CA1177891A CA000378965A CA378965A CA1177891A CA 1177891 A CA1177891 A CA 1177891A CA 000378965 A CA000378965 A CA 000378965A CA 378965 A CA378965 A CA 378965A CA 1177891 A CA1177891 A CA 1177891A
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- Prior art keywords
- tube
- cap
- magnetic
- bore
- relative
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/15—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for use during transport, e.g. by a person, vehicle or boat
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/022—Measuring gradient
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Remote Sensing (AREA)
- Geology (AREA)
- Environmental & Geological Engineering (AREA)
- Engineering & Computer Science (AREA)
- Geophysics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Measuring Magnetic Variables (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
- Transmission And Conversion Of Sensor Element Output (AREA)
- Medicines Containing Antibodies Or Antigens For Use As Internal Diagnostic Agents (AREA)
- Geophysics And Detection Of Objects (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In magnetic sensing apparatus having a pair of directional magnetic field sensors longitudinally spaced apart in a containing tube, mechanical means is provided to compensate for misalignment in the sensor axes. The compensating means takes the form of a non-magnetic member associated with one end of the tube for rotation about the tube axis and a screwed plug of easily magnetizable material contained in a diamet-rically extending threaded bore formed through the rotatable member. Adjustments in the position of the magnetic body relative to the sensors may thus be made by screwing the body inwardly and outwardly of the bore to adjust the radial distance of the magnetic body from the axis of the tube and the orientation of the mag-netic body relative to the sensors may be adjusted by rotating the member in which it is contained relative to the tube.
In magnetic sensing apparatus having a pair of directional magnetic field sensors longitudinally spaced apart in a containing tube, mechanical means is provided to compensate for misalignment in the sensor axes. The compensating means takes the form of a non-magnetic member associated with one end of the tube for rotation about the tube axis and a screwed plug of easily magnetizable material contained in a diamet-rically extending threaded bore formed through the rotatable member. Adjustments in the position of the magnetic body relative to the sensors may thus be made by screwing the body inwardly and outwardly of the bore to adjust the radial distance of the magnetic body from the axis of the tube and the orientation of the mag-netic body relative to the sensors may be adjusted by rotating the member in which it is contained relative to the tube.
Description
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, Erick Oscar Schonstedt MAGNETIC SENSORS HAVING MISALIGNMENT
COMPENSATING MEANS
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` Background of the Invention The invention relates to apparatus for measuring or sensing magnetic phenomena, such as magnetic fields, objects or disturbances, and is more particularly con-cerned with a magnetic locator or gradiometer incorpor-ating mechanically adjustable magnetic compensation - 10 for misalignment of the axes of the magnetic sensor elements.
Saturatable core (fluxgate) magnetic locators or gradiometers comprise at least two electrically matched field-sensing elements mounted on a nonmagnetic structure such that their magnetic axes are, theoreti-cally, strictly parallel or coaxial. The output signals of the two sensors are arranged such that they oppose each other. If the structure is oriented in any direction in a uniform magnetic field, the field components existing at each sensor are equal, so that there is no resulting output signal from the combina-tion of the sensors.
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If a magnetic object exists within the detection range of the instrument, the magnetic field will gen-erally be stronger at one of the sensors than at the other sensor and as a result, the output signal of one î 5 sensor will be greater than that of the other, so that a net difference signal will be produced which is indicative of the presence of the object.
For complete accuracy of operation, the magnetic axes of the two sensors should be precisely lO aligned. The precision required in such alignment is of the order of 3 seconds of arc if the error signal due to misalignment of the magnetic axes is to be less than 1 gamma (10 5 gauss) in an ambient magnetic field of 60,000 gammas. If the magnetic axes of the two 15 sensors are not precisely aligned, the component of the ambient magnetic field existing along the magnetic axis of one sensor will not be the same as the com-ponent of the magnetic field existing along the mag-netic axis of the other sensor. Accordingly, the dif-20 ference between the two sensor signals will not be zero, and a false signal will be obtained due to the mechanical misalignment of the sensors.
In certain prior art fluxgate gradiometers, alignment of the sensors has been achieved by mechani-25 cal adjustment or bending of structural members, such as a tube in which the sensors are mounted. See, for example, applicant's prior U.S. Patent No. 3,050,679, issued August 21, 1962. With this arrangement, after a certain time, the stress may be relieved and the 30 sensors may become misaligned resulting in inaccuracies and the need for readjustment.
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~ 3 ; Another approach to the problem of sensor misalignment is to provide the apparatus with misalign-ment compensating means. Thus, applicant's prior U.S.
Patent No. 3,488,579, issued January 6, 1970, discloses - 5 a system in which misalignment compensation is produced electrically. While this system is capable of compen-`sating for misalignment with high precision, its cost may be higher than is justified when such high accuracy is not required.
It has also been proposed to compensate for extraneous magnetic effects and misaligned cores by providing bodies of easily magnetizable material ad-justably positioned adjacent to a gradiometer. See, for example, U.S. Patent No. 2,966,853, issued ~anuary 3, 1961 to Gilfillan et al; U.S. Patent No. 3,012, 191, issued December 5, 1961 to Miller et al; U.S. Patent - No. 2,976,483, issued March 21, 1961 to Moore et al;
~ and applicant's prior U.S. Patents Nos. 3,487,459, `~ issued December 30, 1969; and 3,757,209, issued Septem-20 ber 4, 1973.
The compensating system disclosed in Patent No.
~ 3,757,209, aforesaid, is of particular interest because .~ it consists of a mechanical compensating means which is mounted on the sensor tube itself without being at-tached in any way to the sensor core, thereby mini-mizing the possibility of creating stresses in the core resulting in sensing errors. Further, by mounting a mechanical compensator on the sensor tube, the system lends itself to use with portable sensing apparatus.
; 30 In one form of sensing apparatus in accordance with Patent No.3,757,209 the mechanical compensator consists of a nonmagnetic annulus surrounding the tube . ~
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and having a magnetic body attached thereto. Theannulus can be moved both around and along the tube to establish the correct position of the magnetic body to obtain optimum compensation. In another form of the apparatus, the mechanical compensator consists of a non-magnetic cap fitting in one end of the sensing tube and having a magnetic body eccentrically fixed on the inside of the cap. Rotation of the cap within the tube adjusts the position of the magnetic body to obtain optimum sensor compensation. This arrangement is more compact than the previously described annulus but is less flexible since there is no facility for adjusting the position of the magnetic compensating body length-wise of the tube.
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Brief Summary of the Invention It is an object of the present invention to provide a magnetic sensing apparatus with mechanical means compensating for sensor misalignment, which means combines both compactness with a desirable range of compensation adjustment.
Another object of the invention is to provide apparatus of the type set out in the preceding paragraph which avoids stressing the magnetic core or support structure therefor.
In its broadest aspect the present invention provides magnetic sensing apparatus including at least two sensing elements mounted on a core within a nonmag-netic tube and means for mechanically compensating for . misalignment of such elements, the compensating means comprising a nonmagnetic member carried by the tube for rotation about the tube axis and a body of easily magnetizable material carried by the nonmagnetic member r a17~
in a manner permitting adjustment of the position of this body relative to the nonmagnetic member.
In a preferred form of the invention, the nonmagnetic member forms an end cap for the snsor tube or is attached to the outside of the end cap and the magnetic body comprises a plug threaded into a radially : extending bore in the nonmagnetic member. With this arrangement, adjustments can be made both in the ro-tational orientation of the magnetic body relative to the tube by suitable positioning of the end cap about the tube axis, and also to the radial distance of the . body from the tube axis by adjusting movements of the magnetic body within the threaded bore.
It has been found that this facility for adjust-ing the radial distance of the magnetic body from thetube axis, which is not available in apparatus as dis-closed for examp].e in U~S. Patent No. 3,757,209 con-I tributes significantly to the degree of flexibility offered by the instrument. Moreover, the magnetic body :; 20 can be made accessible from the exterior of the tube so that adjustments both of this body and of the non-magnetic member are thereby facilitated.
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Brief Description of the ~rawings The invention is described, by way of example only, with reference to the accompanying drawings.
i Figure 1 is a plan view of a first embodiment of magnetic sensing apparatus in accordance with the ,` invention;
Figure 2 is a sectional view of the distal end portion of the apparatus shown in Figure l;
Figure 3 ls an end view, with the cover removed, of the tube shown in Figure 2;
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Figure 4 is a sectional elevation of part of a second embodiment of a magnetic sensing apparatus in accordance with the invention; and Figure 5 is an end view oE the apparatus shown in Figure 4.
Description of Preferred Embodiments :
Referring to Figure l, reference numeral 10 designates magnetic sensing or detecting apparatus, such as a magnetic locator, employing compensating means in accordance with the invention. The locator which may be employed for locating hidden utility pipes, surveyor's bench marks, etc. comprises a cylindrical ; case 12, containing electronics, and a nonmagnetic sensor-containing tube 14 extending from the case 12.
The apparatus is portable in use and the distal end of tube 14 may be swept back and forth along the ground in a scanning motion. A distinctive signal is produced in earphones 16 when a magnetic object is located.
Tube 14 which is formed of nonmagnetic material such as aluminum, for example, contains magnetic field sensors A and B mounted on a suitable core having a friction fit in tube 14 in known manner. Sensors of the fluxgate type suitable for use in the apparatus are disclosed, for example, in applicant's prior U.S.
- 25 Patent No. 2,981,885, issued April 25, 1961. The sen-sors per se and the electronics associated therewith are well known, and will not therefore be described herein in detail. A suitable sensor may, for example, comprise a tubular magnetic core having excitation windings wound longitudinally through the core and hav-~ ing pickup windings wound circumferentially about the ;~ core. In operation, the excitation windings are sup-plied with alternating current by an oscillator. Second .
, .
~ 3 1 ` harmonic fluxes generated in the sensor cores due to the e~fect of an external magnetic field acting along the core axes (parallel to the length of the cores) cut the pickup windings and generate second harmonic output voltages therein. The output voltages from the sensor are applied differentially to suitable - measuring apparatus so that if the sensors are matched and, if their axes are perfectly aligned, the meter will read zero in a uniform field. If, however, there is a misalignment of one of the core axes, an error ;; signal will be generated due to such misalignment.
The present invention is not concerned with the precise manner of mounting the sensors and windings . therefor, nor with the precise manner in which the .: 15 signals from the fluxgate sensors are detected. It will be apparent, however, to those skilled in the art that the sensors A and B may be mounted substantially co-axially upon a ceramic core, as described in aforesaid U.S. Patent No. 3,487,459 which may then be press-~ .
fitted into tube 14 as indicated, with wires from the respective sensors passing through tube 14 and into the case 12 (with the possible interposition of electric . plug and socket connections between the tube and case, as indicated), the case containing the oscillator, amplifier, etc.
. As previously indicated, to obtain precise - alignment of the longitudinal axes of sensors A and B
is an expensive and tedious operation. Therefore, in . accordance with the invention, means is provided for obtaining mechanical compensation for misalignment of the sensor axes. To this end, tube 14 is provided with an end cap 18 of nonmagnetic material, such as hard syn-thetic plastic material, this end cap containing a plug ,. , ., ;, .., r, `:;
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20 of easily magnetizable material, for example ; Permalloy. An 0-ring seal 22 fits between cap 20 and tube 14 and provides resistance to turning of cap 20 . so that the cap will stay in a particular orientation S to which it is rotated relative to tube 14.
Plug 20 is in the form of a screw contained within a threaded bore 24 extending diametrically through the end cap. Thus, the radial distance of plug 20 relative to the axis of tube 14 can be adjusted by screwing the plug inwardly or outwardly relative to bore 24. Externally, end cap 18 is provided with open-ings 26 for a wrench or the like which may be used to rotate the end cap relative to tube 14.
In use, the orientation of plug 20 relative to sensors A and B can be adjusted by rotating end cap 20 within tube 14, and the radial distance of the plug relative to the tube axis can be adjusted by screwing the plug within bore 24. These two variables may be used to obtain the correct positioning for plug 20, in order to obtain optimum compensation fo. misalignment of the sensors A ~nd B. The theory in obtaining such ; mechanical compensation will not be described herein in detail and is adequately dealt with in the above-mentioned U.S. Patent Nos . 3, 757, 209 and 3, 487, 459 .
In order to adjust the compensating mechanism of the invention, to obtain optimum compensation for : misalignment of sensors A and B, the apparatus 10 may !~ be placed in a fixture (not shown) so that it can be rotated about the axis of tube 14 in an ambient magnetic : 30 field perpendicular to this axis. If the axes of the sensors A and B are not precisely aligned with or parallel to the axis of tube 14, a signal will be ;
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generated when the assembly is turned about the axis of the tube. The position o~ plug 20 may then be adjusted either radially in bore 24 or by rotation of cap 18, or both, in order to minimize the generated signal.
When the optimum positioning of plug 20 is obtained, the plug may be fixed within bore 24 by cement, to ~: prevent it from turning, and a cup-like cover 28 of resilient material such as rubber is then positioned over the end of tube 14 to embrace both the cap and the end of the tube.
A second form of magnetic sensing apparatus in accordance with the invention is illustrated in Fig-ures 4 and 5 and like reference numerals are used to denote the parts thereof corresponding to parts of the previously described embodiment. In this case, tube .' 14 is provided with a plastic end cap 18a and an O-ring seal 22a is again provided between the end cap and tube 14. Cap 18a may in this case be non-rotatably mounted in the end of the tube.
The mechanical compensating mechanism in this embodiment takes the form of a cylindrical plastic , plate 30 rotatably mounted in a recess on the exterior , of end cap 18a and held in place by brackets 32 screwed into the end cap by means of screws 34. Plate 30 is again provided with a diametrically extending threaded bore 24a containing the plug 20a of easily magnetizable material. Plate 30 has external formations 26a and 26b allowing the plate to be rotated relative to end cap 18a when the brackets 32 are suitably loosened.
,~ 30 It will be appreciated that adjustments in the compensating mechanism in this embodiment are made in ;l a similar manner as with the previously described em-b~dyment. ~hus, plu~ 20a may be screwed inwardly and "' lo ~77~
ou~wardly within bore 2~a to adjust its radial distance relative to the axis of tube 14 and may again be ce-~; mented in place. The orientation of plug 20a relative to sensors A and B can again be adjusted by suitably rotating plate 30 in end cap 18a and then tighteningthe plate down by means of screws 34.
It will be seen that the invention provides misalignment compensating means for magnetic sensing apparatus, which means offers a relatively wide range of adjustment while providing a compact structure without internal modification of the sensing equipment and which is readily adaptable to the tube containing such equipment. Further, adjustments of the compen-sating means can be made wholly from the exterior of the tube without requiring the removal of the end cap, thereby facilitating its use.
; While the invention is particularly suitable for use on portable type gradiometers and the like, as shown in Figure 1, it is not limited to this applica-; 20 tion, and the described compensating means can be :;~ used on other types of magnetic sensing apparatus which ;~ include a pair of magnetic sensors within a nonmag-: netic tube.
- While only preferred embodiments of the invention ;.......... 25 have been described herein in detail, it will be ~ appreciated that numerous modifications may be made .-. . within the scope of the attached claims. For example, i~ the compensating means of the invention may, in an : alternative form, comprise an annulus mounted for both longitudinal and rotary movement on tube 14 and incor-porating a radial~y extending ~hreaded bore accommo-dating a screwed plug of magnetic material. This form .
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,, . of the invention offers an additional axis of compen-sation compared with the previously described embodi-ments, namely longitudinally of tube 14, but the arrangement is not as compac~ as those previously described.
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, Erick Oscar Schonstedt MAGNETIC SENSORS HAVING MISALIGNMENT
COMPENSATING MEANS
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` Background of the Invention The invention relates to apparatus for measuring or sensing magnetic phenomena, such as magnetic fields, objects or disturbances, and is more particularly con-cerned with a magnetic locator or gradiometer incorpor-ating mechanically adjustable magnetic compensation - 10 for misalignment of the axes of the magnetic sensor elements.
Saturatable core (fluxgate) magnetic locators or gradiometers comprise at least two electrically matched field-sensing elements mounted on a nonmagnetic structure such that their magnetic axes are, theoreti-cally, strictly parallel or coaxial. The output signals of the two sensors are arranged such that they oppose each other. If the structure is oriented in any direction in a uniform magnetic field, the field components existing at each sensor are equal, so that there is no resulting output signal from the combina-tion of the sensors.
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If a magnetic object exists within the detection range of the instrument, the magnetic field will gen-erally be stronger at one of the sensors than at the other sensor and as a result, the output signal of one î 5 sensor will be greater than that of the other, so that a net difference signal will be produced which is indicative of the presence of the object.
For complete accuracy of operation, the magnetic axes of the two sensors should be precisely lO aligned. The precision required in such alignment is of the order of 3 seconds of arc if the error signal due to misalignment of the magnetic axes is to be less than 1 gamma (10 5 gauss) in an ambient magnetic field of 60,000 gammas. If the magnetic axes of the two 15 sensors are not precisely aligned, the component of the ambient magnetic field existing along the magnetic axis of one sensor will not be the same as the com-ponent of the magnetic field existing along the mag-netic axis of the other sensor. Accordingly, the dif-20 ference between the two sensor signals will not be zero, and a false signal will be obtained due to the mechanical misalignment of the sensors.
In certain prior art fluxgate gradiometers, alignment of the sensors has been achieved by mechani-25 cal adjustment or bending of structural members, such as a tube in which the sensors are mounted. See, for example, applicant's prior U.S. Patent No. 3,050,679, issued August 21, 1962. With this arrangement, after a certain time, the stress may be relieved and the 30 sensors may become misaligned resulting in inaccuracies and the need for readjustment.
~ ~7'78~
~ 3 ; Another approach to the problem of sensor misalignment is to provide the apparatus with misalign-ment compensating means. Thus, applicant's prior U.S.
Patent No. 3,488,579, issued January 6, 1970, discloses - 5 a system in which misalignment compensation is produced electrically. While this system is capable of compen-`sating for misalignment with high precision, its cost may be higher than is justified when such high accuracy is not required.
It has also been proposed to compensate for extraneous magnetic effects and misaligned cores by providing bodies of easily magnetizable material ad-justably positioned adjacent to a gradiometer. See, for example, U.S. Patent No. 2,966,853, issued ~anuary 3, 1961 to Gilfillan et al; U.S. Patent No. 3,012, 191, issued December 5, 1961 to Miller et al; U.S. Patent - No. 2,976,483, issued March 21, 1961 to Moore et al;
~ and applicant's prior U.S. Patents Nos. 3,487,459, `~ issued December 30, 1969; and 3,757,209, issued Septem-20 ber 4, 1973.
The compensating system disclosed in Patent No.
~ 3,757,209, aforesaid, is of particular interest because .~ it consists of a mechanical compensating means which is mounted on the sensor tube itself without being at-tached in any way to the sensor core, thereby mini-mizing the possibility of creating stresses in the core resulting in sensing errors. Further, by mounting a mechanical compensator on the sensor tube, the system lends itself to use with portable sensing apparatus.
; 30 In one form of sensing apparatus in accordance with Patent No.3,757,209 the mechanical compensator consists of a nonmagnetic annulus surrounding the tube . ~
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and having a magnetic body attached thereto. Theannulus can be moved both around and along the tube to establish the correct position of the magnetic body to obtain optimum compensation. In another form of the apparatus, the mechanical compensator consists of a non-magnetic cap fitting in one end of the sensing tube and having a magnetic body eccentrically fixed on the inside of the cap. Rotation of the cap within the tube adjusts the position of the magnetic body to obtain optimum sensor compensation. This arrangement is more compact than the previously described annulus but is less flexible since there is no facility for adjusting the position of the magnetic compensating body length-wise of the tube.
. .
Brief Summary of the Invention It is an object of the present invention to provide a magnetic sensing apparatus with mechanical means compensating for sensor misalignment, which means combines both compactness with a desirable range of compensation adjustment.
Another object of the invention is to provide apparatus of the type set out in the preceding paragraph which avoids stressing the magnetic core or support structure therefor.
In its broadest aspect the present invention provides magnetic sensing apparatus including at least two sensing elements mounted on a core within a nonmag-netic tube and means for mechanically compensating for . misalignment of such elements, the compensating means comprising a nonmagnetic member carried by the tube for rotation about the tube axis and a body of easily magnetizable material carried by the nonmagnetic member r a17~
in a manner permitting adjustment of the position of this body relative to the nonmagnetic member.
In a preferred form of the invention, the nonmagnetic member forms an end cap for the snsor tube or is attached to the outside of the end cap and the magnetic body comprises a plug threaded into a radially : extending bore in the nonmagnetic member. With this arrangement, adjustments can be made both in the ro-tational orientation of the magnetic body relative to the tube by suitable positioning of the end cap about the tube axis, and also to the radial distance of the . body from the tube axis by adjusting movements of the magnetic body within the threaded bore.
It has been found that this facility for adjust-ing the radial distance of the magnetic body from thetube axis, which is not available in apparatus as dis-closed for examp].e in U~S. Patent No. 3,757,209 con-I tributes significantly to the degree of flexibility offered by the instrument. Moreover, the magnetic body :; 20 can be made accessible from the exterior of the tube so that adjustments both of this body and of the non-magnetic member are thereby facilitated.
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Brief Description of the ~rawings The invention is described, by way of example only, with reference to the accompanying drawings.
i Figure 1 is a plan view of a first embodiment of magnetic sensing apparatus in accordance with the ,` invention;
Figure 2 is a sectional view of the distal end portion of the apparatus shown in Figure l;
Figure 3 ls an end view, with the cover removed, of the tube shown in Figure 2;
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Figure 4 is a sectional elevation of part of a second embodiment of a magnetic sensing apparatus in accordance with the invention; and Figure 5 is an end view oE the apparatus shown in Figure 4.
Description of Preferred Embodiments :
Referring to Figure l, reference numeral 10 designates magnetic sensing or detecting apparatus, such as a magnetic locator, employing compensating means in accordance with the invention. The locator which may be employed for locating hidden utility pipes, surveyor's bench marks, etc. comprises a cylindrical ; case 12, containing electronics, and a nonmagnetic sensor-containing tube 14 extending from the case 12.
The apparatus is portable in use and the distal end of tube 14 may be swept back and forth along the ground in a scanning motion. A distinctive signal is produced in earphones 16 when a magnetic object is located.
Tube 14 which is formed of nonmagnetic material such as aluminum, for example, contains magnetic field sensors A and B mounted on a suitable core having a friction fit in tube 14 in known manner. Sensors of the fluxgate type suitable for use in the apparatus are disclosed, for example, in applicant's prior U.S.
- 25 Patent No. 2,981,885, issued April 25, 1961. The sen-sors per se and the electronics associated therewith are well known, and will not therefore be described herein in detail. A suitable sensor may, for example, comprise a tubular magnetic core having excitation windings wound longitudinally through the core and hav-~ ing pickup windings wound circumferentially about the ;~ core. In operation, the excitation windings are sup-plied with alternating current by an oscillator. Second .
, .
~ 3 1 ` harmonic fluxes generated in the sensor cores due to the e~fect of an external magnetic field acting along the core axes (parallel to the length of the cores) cut the pickup windings and generate second harmonic output voltages therein. The output voltages from the sensor are applied differentially to suitable - measuring apparatus so that if the sensors are matched and, if their axes are perfectly aligned, the meter will read zero in a uniform field. If, however, there is a misalignment of one of the core axes, an error ;; signal will be generated due to such misalignment.
The present invention is not concerned with the precise manner of mounting the sensors and windings . therefor, nor with the precise manner in which the .: 15 signals from the fluxgate sensors are detected. It will be apparent, however, to those skilled in the art that the sensors A and B may be mounted substantially co-axially upon a ceramic core, as described in aforesaid U.S. Patent No. 3,487,459 which may then be press-~ .
fitted into tube 14 as indicated, with wires from the respective sensors passing through tube 14 and into the case 12 (with the possible interposition of electric . plug and socket connections between the tube and case, as indicated), the case containing the oscillator, amplifier, etc.
. As previously indicated, to obtain precise - alignment of the longitudinal axes of sensors A and B
is an expensive and tedious operation. Therefore, in . accordance with the invention, means is provided for obtaining mechanical compensation for misalignment of the sensor axes. To this end, tube 14 is provided with an end cap 18 of nonmagnetic material, such as hard syn-thetic plastic material, this end cap containing a plug ,. , ., ;, .., r, `:;
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20 of easily magnetizable material, for example ; Permalloy. An 0-ring seal 22 fits between cap 20 and tube 14 and provides resistance to turning of cap 20 . so that the cap will stay in a particular orientation S to which it is rotated relative to tube 14.
Plug 20 is in the form of a screw contained within a threaded bore 24 extending diametrically through the end cap. Thus, the radial distance of plug 20 relative to the axis of tube 14 can be adjusted by screwing the plug inwardly or outwardly relative to bore 24. Externally, end cap 18 is provided with open-ings 26 for a wrench or the like which may be used to rotate the end cap relative to tube 14.
In use, the orientation of plug 20 relative to sensors A and B can be adjusted by rotating end cap 20 within tube 14, and the radial distance of the plug relative to the tube axis can be adjusted by screwing the plug within bore 24. These two variables may be used to obtain the correct positioning for plug 20, in order to obtain optimum compensation fo. misalignment of the sensors A ~nd B. The theory in obtaining such ; mechanical compensation will not be described herein in detail and is adequately dealt with in the above-mentioned U.S. Patent Nos . 3, 757, 209 and 3, 487, 459 .
In order to adjust the compensating mechanism of the invention, to obtain optimum compensation for : misalignment of sensors A and B, the apparatus 10 may !~ be placed in a fixture (not shown) so that it can be rotated about the axis of tube 14 in an ambient magnetic : 30 field perpendicular to this axis. If the axes of the sensors A and B are not precisely aligned with or parallel to the axis of tube 14, a signal will be ;
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generated when the assembly is turned about the axis of the tube. The position o~ plug 20 may then be adjusted either radially in bore 24 or by rotation of cap 18, or both, in order to minimize the generated signal.
When the optimum positioning of plug 20 is obtained, the plug may be fixed within bore 24 by cement, to ~: prevent it from turning, and a cup-like cover 28 of resilient material such as rubber is then positioned over the end of tube 14 to embrace both the cap and the end of the tube.
A second form of magnetic sensing apparatus in accordance with the invention is illustrated in Fig-ures 4 and 5 and like reference numerals are used to denote the parts thereof corresponding to parts of the previously described embodiment. In this case, tube .' 14 is provided with a plastic end cap 18a and an O-ring seal 22a is again provided between the end cap and tube 14. Cap 18a may in this case be non-rotatably mounted in the end of the tube.
The mechanical compensating mechanism in this embodiment takes the form of a cylindrical plastic , plate 30 rotatably mounted in a recess on the exterior , of end cap 18a and held in place by brackets 32 screwed into the end cap by means of screws 34. Plate 30 is again provided with a diametrically extending threaded bore 24a containing the plug 20a of easily magnetizable material. Plate 30 has external formations 26a and 26b allowing the plate to be rotated relative to end cap 18a when the brackets 32 are suitably loosened.
,~ 30 It will be appreciated that adjustments in the compensating mechanism in this embodiment are made in ;l a similar manner as with the previously described em-b~dyment. ~hus, plu~ 20a may be screwed inwardly and "' lo ~77~
ou~wardly within bore 2~a to adjust its radial distance relative to the axis of tube 14 and may again be ce-~; mented in place. The orientation of plug 20a relative to sensors A and B can again be adjusted by suitably rotating plate 30 in end cap 18a and then tighteningthe plate down by means of screws 34.
It will be seen that the invention provides misalignment compensating means for magnetic sensing apparatus, which means offers a relatively wide range of adjustment while providing a compact structure without internal modification of the sensing equipment and which is readily adaptable to the tube containing such equipment. Further, adjustments of the compen-sating means can be made wholly from the exterior of the tube without requiring the removal of the end cap, thereby facilitating its use.
; While the invention is particularly suitable for use on portable type gradiometers and the like, as shown in Figure 1, it is not limited to this applica-; 20 tion, and the described compensating means can be :;~ used on other types of magnetic sensing apparatus which ;~ include a pair of magnetic sensors within a nonmag-: netic tube.
- While only preferred embodiments of the invention ;.......... 25 have been described herein in detail, it will be ~ appreciated that numerous modifications may be made .-. . within the scope of the attached claims. For example, i~ the compensating means of the invention may, in an : alternative form, comprise an annulus mounted for both longitudinal and rotary movement on tube 14 and incor-porating a radial~y extending ~hreaded bore accommo-dating a screwed plug of magnetic material. This form .
:..
. .
'~
,.
77~
,, . of the invention offers an additional axis of compen-sation compared with the previously described embodi-ments, namely longitudinally of tube 14, but the arrangement is not as compac~ as those previously described.
!
., '~
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., , :' ,'
Claims (11)
1. Magnetic sensing apparatus comprising an elongated nonmagnetic tube containing a pair of directional magnetic field sensor means longitudinally spaced apart in said tube and having individual magnetic axes approximately aligned with the longitudinal axis of said tube, and means for compensating for misalignment of the axis of either of said sensor means with said longitudinal axis, said compensating means comprising a nonmagnetic end cap carried by said tube, a body of easily magnetizable material carried by said end cap in a position accessible from the exterior of the tube, means for adjusting the circumferential orientation of said body relative to said longitudinal axis and means for adjusting the distance of said body from said longitudinal axis whereby adjustments in the position of said body both circumferentially and radially of the tube may be made without removing the end cap from the tube.
2. The apparatus defined in claim 1, wherein said means for adjusting the distance of said body from said longitudinal axis comprises means for radially adjusting the position of said body relative to said end cap.
3. The apparatus as defined in claim l or claim 2, wherein said means for adjusting the circumferential orientation of said body relative to said axis comprises means permitting rotational adjustment of said nonmagnetic end cap on said tube.
4. The apparatus as defined in claim 2, wherein said means for adjusting the position of said body relative to said member comprises a screw threaded bore formed in said end cap, and said body comprising a threaded plug screwed into said bore.
5. The apparatus defined in claim 1, wherein said cap has a friction fit with said tube permitting rotational adjustment of said cap about said longitudinal axis for adjusting the circumferential orientation of said body.
6. The apparatus defined in claim 5, wherein said cap includes a threaded radially extending bore and said body comprises a threaded plug screwed into said bore.
7. The apparatus as defined in claim 6, wherein said bore is located in a portion of said cap protruding from said tube.
8. The apparatus as defined in claim 7, including a cup-shaped cover embracing said cap and an end portion of said tube.
9. The apparatus as defined in claim 1, wherein said body is carried in a plate member mounted on the exterior of said cap for rotational adjustment relative to said cap to adjust the circumferential orientation of said body relative to said axis.
10. The apparatus as defined in claim 9, wehrein said plate member includes a radially extending threaded bore and said body comprises a threaded plug screwed into said bore.
11. The apparatus as defined in claim 9 or claim 10, including releasable bracket means securing said plate member to said cap for rotational adjustment of said plate member relative to said cap.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16248980A | 1980-06-24 | 1980-06-24 | |
| US162,489 | 1980-06-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1177891A true CA1177891A (en) | 1984-11-13 |
Family
ID=22585840
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000378965A Expired CA1177891A (en) | 1980-06-24 | 1981-06-03 | Magnetic sensors having misalignment compensating means |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5730965A (en) |
| CA (1) | CA1177891A (en) |
| DE (1) | DE3124255C2 (en) |
| FR (1) | FR2485751A1 (en) |
| GB (1) | GB2078968B (en) |
| NO (1) | NO155025C (en) |
| SE (1) | SE445956B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0125741B1 (en) * | 1983-01-20 | 1990-08-08 | Scopemoor Limited | Detector for buried objects |
| GB2135460B (en) * | 1983-01-20 | 1987-10-07 | Scopemoor Ltd | Detecting hidden objects |
| JPH0792499B2 (en) * | 1984-08-08 | 1995-10-09 | 三菱電機株式会社 | Magnetic field probe positioning device |
| FR2582905B1 (en) * | 1985-06-07 | 1989-08-25 | Agot Aime | DETECTION DEVICE FOR ANIMALS. |
| GB2230341B (en) * | 1989-01-28 | 1994-01-05 | Cambridge Engineering Design L | Apparatus for and method of measuring magnetic flux density |
| DE4210905A1 (en) * | 1992-04-02 | 1993-10-07 | Steingroever Magnet Physik | Magnetic field sensor with acoustic indicator - uses magnetic field dependent sensor which transmits acoustic signal proportional to strength or direction of magnetic field |
| DE4232466A1 (en) * | 1992-09-28 | 1994-03-31 | Klaus Ebinger | Magnetometer probe |
| CN103229056B (en) | 2010-11-30 | 2015-06-24 | 皇家飞利浦电子股份有限公司 | A sensor device for magnetically actuated particles |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2966853A (en) * | 1941-10-27 | 1961-01-03 | Jr Edward S Gilfillan | Buoyant mine with gradiometer |
| US2981885A (en) * | 1958-07-21 | 1961-04-25 | Erick O Schonstedt | Saturable measuring device and magnetic core therefor |
| US3050679A (en) * | 1960-02-18 | 1962-08-21 | Erick O Schonstedt | Device for detecting or measuring magnetic fields |
| US3487459A (en) * | 1968-03-28 | 1969-12-30 | Erick O Schonstedt | Induced magnetic compensation for misalignment of magnetic gradiometer sensors |
| US3488579A (en) * | 1969-04-01 | 1970-01-06 | Erick O Schonstedt | Magnetic gradiometer apparatus with misalignment compensation |
| US3757209A (en) * | 1972-02-11 | 1973-09-04 | E Schonstedt | Compensation for misalignment of magnetic sensors |
| US3961245A (en) * | 1974-11-20 | 1976-06-01 | Schonstedt Instrument Company | Magnetic locator having improved sensors |
| DE2929404C2 (en) * | 1979-07-20 | 1983-10-27 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Differential field probe |
-
1981
- 1981-05-28 GB GB8116312A patent/GB2078968B/en not_active Expired
- 1981-06-03 CA CA000378965A patent/CA1177891A/en not_active Expired
- 1981-06-05 SE SE8103541A patent/SE445956B/en not_active IP Right Cessation
- 1981-06-05 NO NO811927A patent/NO155025C/en unknown
- 1981-06-19 DE DE3124255A patent/DE3124255C2/en not_active Expired
- 1981-06-23 FR FR8112295A patent/FR2485751A1/en active Granted
- 1981-06-24 JP JP9679181A patent/JPS5730965A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| NO155025C (en) | 1987-01-28 |
| DE3124255A1 (en) | 1982-06-24 |
| NO155025B (en) | 1986-10-20 |
| JPS5730965A (en) | 1982-02-19 |
| SE8103541L (en) | 1981-12-25 |
| SE445956B (en) | 1986-07-28 |
| GB2078968A (en) | 1982-01-13 |
| DE3124255C2 (en) | 1985-05-09 |
| NO811927L (en) | 1981-12-28 |
| FR2485751B1 (en) | 1984-11-30 |
| GB2078968B (en) | 1984-07-25 |
| FR2485751A1 (en) | 1981-12-31 |
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