CA1289621C - Frequency difference digital compass and magnetometer - Google Patents
Frequency difference digital compass and magnetometerInfo
- Publication number
- CA1289621C CA1289621C CA000570993A CA570993A CA1289621C CA 1289621 C CA1289621 C CA 1289621C CA 000570993 A CA000570993 A CA 000570993A CA 570993 A CA570993 A CA 570993A CA 1289621 C CA1289621 C CA 1289621C
- Authority
- CA
- Canada
- Prior art keywords
- coil
- magnetic field
- oscillator
- axis
- providing
- 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 - Lifetime
Links
Classifications
-
- 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C17/00—Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes
- G01C17/02—Magnetic compasses
- G01C17/28—Electromagnetic compasses
Abstract
ABSTRACT OF THE DISCLOSURE
A digital compass (20) has a sensing coil (60) wound on an elongated strip of high direct current permeability magnetic material. The sensing coil (60) is connected to a sensing circuit (56). The sensing coil and sensing circuit are responsive to the Earth's magnetic field to provide an oscillating signal at an output (28) of the sensing circuit (56) which varies in frequency with orientation of the at least one sensing coil (60) with respect to the Earth's magnetic field. A microprocessor (36) is connected to receive information inputs from the oscillating signal. The microprocessor converts the information inputs to an indication of orientation of the sensing coil with respect to the Earth's magnetic field based on the frequency of the oscillating signal. A
display (52) receives the orientation indication from the microprocessor.
A digital compass (20) has a sensing coil (60) wound on an elongated strip of high direct current permeability magnetic material. The sensing coil (60) is connected to a sensing circuit (56). The sensing coil and sensing circuit are responsive to the Earth's magnetic field to provide an oscillating signal at an output (28) of the sensing circuit (56) which varies in frequency with orientation of the at least one sensing coil (60) with respect to the Earth's magnetic field. A microprocessor (36) is connected to receive information inputs from the oscillating signal. The microprocessor converts the information inputs to an indication of orientation of the sensing coil with respect to the Earth's magnetic field based on the frequency of the oscillating signal. A
display (52) receives the orientation indication from the microprocessor.
Description
FR13QUENCY DIFFERENt::E DIGITAL COMPAS~ NET~13TER
13ACKGROUND O~ E INVENTION
~ hi~ imtentlon r~late~ to a digltal co:~pa~s in which dl~ction oX ths ~arth ' ~ ~agnetlo ~iald ~ deter~ined on th~ ba~i~ oP frQquen~y differences which ara ~ ~unction Or th~ ori~ntatlon o:~ th~ dlgital c:~pas~ wlth r~pe~t to ths~
Earthl~ ~agn~tlc ~ield. Mor~ parttcularly, it r~31a~es~ ~o ~uoh G digital compa~ ~n whioh it l# not n~c~ary ~o conv~rt ~nalog signal~ ts digital ~ignals. It ~urth~r relat~ to a novel r~o~m of a ~açln~to~eter whlch h~
g~nQral ~pllca~ion ~or dQtRrmining orlen~a~ion o~ w~aX
~as~n~tic ~ields based on ~regu~ncy di~rea~c~.
13ACKGROUND O~ E INVENTION
~ hi~ imtentlon r~late~ to a digltal co:~pa~s in which dl~ction oX ths ~arth ' ~ ~agnetlo ~iald ~ deter~ined on th~ ba~i~ oP frQquen~y differences which ara ~ ~unction Or th~ ori~ntatlon o:~ th~ dlgital c:~pas~ wlth r~pe~t to ths~
Earthl~ ~agn~tlc ~ield. Mor~ parttcularly, it r~31a~es~ ~o ~uoh G digital compa~ ~n whioh it l# not n~c~ary ~o conv~rt ~nalog signal~ ts digital ~ignals. It ~urth~r relat~ to a novel r~o~m of a ~açln~to~eter whlch h~
g~nQral ~pllca~ion ~or dQtRrmining orlen~a~ion o~ w~aX
~as~n~tic ~ields based on ~regu~ncy di~rea~c~.
2. Pe~ori,~?tloll ~f ~ P~;Lor ~
A vari~ty o~ digital compa~es and magneto~et~r~ ars l~nown ~n thQ ~rt. For example, U.S. ~atent 3,396,329, i~u~d P.ugu3t 6, 1~8 to Salvi diE~close~; a ~nagn~toraeter in wh~ch th~ ~ntensidcy o~ w~ak m~gn~tie ~ield~ urlotion o~ ~x~ n~y diP~erenca ln ~n~ed ~lgnal~, but ind~p~ndQnt o~ orientation Or a vo8sel in which the ~agnetom~ter 1 ~n~tall~d. U.~. ~atGnt 3,634,946, i~ ed Januury 18, 1972 to ~tar, r~late~ to an all d~git~l clrcuit impl~ntation o~ ~ digital compa~s which opexa~s on the ba~i~ o~
~patial ralatiorl~hips oP pulee~ produced when a ~n30r i~
a~igal~3d in a re~erenae d~ ~eotion and orthogonal to the Earth ' ~ magn~tio ~ield . There is no m~ ntion ln thie P.-4602 0/W~H
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patant OI fregu~ncy differ~nce3 creatsd by orian'c~tion, nor doe~ the circu~ t 6hown di~criminatQ on tha basis o~
~uch îrequency differ~nce~. U.S~ Patent 4,305,034~ u~d ~cemb~r ~, 1981 to ~02lg ~t al. di~alo~e~ a loagn~tomQ~sr ~n whlch ~requency change~ are oxeated when a background magnetlc ~i~ld, which can be the Earth'~ magnetic ~lald, i~ perturbed by a Dlatal ob~ ect, but ~hi~ d~vi¢~ ~anno~
provide ~ign ln~ormation, i~ e., whether the ~i~ld i~
parallel or antiparallel to the sQnsor aoil . U. S . Pat~n~
4,340,861, issued July 20, 1982 to 8p~rks, di~lo~es a ~nagnetometer in which ~requancy differQnces ar~ u~4d to detQrmine distribution o~ magneti~ ~iQld~ producQd by p~rman~nk magnet~, on tha basi~ of amplitud~ in~or:mation ~n thel di~fsr~nt ~r~quQncy sign~l~. U.8.S.R. ~a~ont 945j835, i~au~d July 27, 1982 to Bon~ar~l3vsk e3t al. di~-c:lo~es that a ~trong ma~n~tlG ~leld wlll produc~ ~r0quQncy di~3r~nces in an LC circuitD
~ h~ ~ollowing additlonal issued U. S. patent~ rolata to digital compas~es which utll~ ze phase di~r~nc~, compari~on w~ th prevlou~ ~ignals at known orient~lon~ or courltinq o~ s~n~ing ~arka to dQterminQ ori~ntation:
A vari~ty o~ digital compa~es and magneto~et~r~ ars l~nown ~n thQ ~rt. For example, U.S. ~atent 3,396,329, i~u~d P.ugu3t 6, 1~8 to Salvi diE~close~; a ~nagn~toraeter in wh~ch th~ ~ntensidcy o~ w~ak m~gn~tie ~ield~ urlotion o~ ~x~ n~y diP~erenca ln ~n~ed ~lgnal~, but ind~p~ndQnt o~ orientation Or a vo8sel in which the ~agnetom~ter 1 ~n~tall~d. U.~. ~atGnt 3,634,946, i~ ed Januury 18, 1972 to ~tar, r~late~ to an all d~git~l clrcuit impl~ntation o~ ~ digital compa~s which opexa~s on the ba~i~ o~
~patial ralatiorl~hips oP pulee~ produced when a ~n30r i~
a~igal~3d in a re~erenae d~ ~eotion and orthogonal to the Earth ' ~ magn~tio ~ield . There is no m~ ntion ln thie P.-4602 0/W~H
~g ' .
.
.
' ; :
, ,: . ' `
3L2~2~L
patant OI fregu~ncy differ~nce3 creatsd by orian'c~tion, nor doe~ the circu~ t 6hown di~criminatQ on tha basis o~
~uch îrequency differ~nce~. U.S~ Patent 4,305,034~ u~d ~cemb~r ~, 1981 to ~02lg ~t al. di~alo~e~ a loagn~tomQ~sr ~n whlch ~requency change~ are oxeated when a background magnetlc ~i~ld, which can be the Earth'~ magnetic ~lald, i~ perturbed by a Dlatal ob~ ect, but ~hi~ d~vi¢~ ~anno~
provide ~ign ln~ormation, i~ e., whether the ~i~ld i~
parallel or antiparallel to the sQnsor aoil . U. S . Pat~n~
4,340,861, issued July 20, 1982 to 8p~rks, di~lo~es a ~nagnetometer in which ~requancy differQnces ar~ u~4d to detQrmine distribution o~ magneti~ ~iQld~ producQd by p~rman~nk magnet~, on tha basi~ of amplitud~ in~or:mation ~n thel di~fsr~nt ~r~quQncy sign~l~. U.8.S.R. ~a~ont 945j835, i~au~d July 27, 1982 to Bon~ar~l3vsk e3t al. di~-c:lo~es that a ~trong ma~n~tlG ~leld wlll produc~ ~r0quQncy di~3r~nces in an LC circuitD
~ h~ ~ollowing additlonal issued U. S. patent~ rolata to digital compas~es which utll~ ze phase di~r~nc~, compari~on w~ th prevlou~ ~ignals at known orient~lon~ or courltinq o~ s~n~ing ~arka to dQterminQ ori~ntation:
3,490,024, i~sued Janu~ry 13, 1970 to Sh~rrill et æ.l.s 3,903,610, $~uad Septembar 9, 1970 to H~avi~id~ e~ al. J
3,952,420,~ is~u~d ~prll 27, lg76 to BQn~aD~in ~t al.
3,952,420,~ is~u~d ~prll 27, lg76 to BQn~aD~in ~t al.
4,09~,348, ie~u~d ,June 20, 1978 to Xr~m~r~ 4,17g,741, ~eu~d De¢~mbor 18, 1g7g to Ro~anis 4,424,631, :L~u~d J~nuary 10, 1984 to Frank~ and 4,640,016, l~ued Fabruary 3, 19~7 to Tannar e'c al . Th~ ~ollowin~ is3u~d t~ . 8 .
patent~ relate gan~rally l:o magnetomot~ros 3,432,751, ~ued March 11, 1969 to Godby Qt al. S 3,435,337, i~uad Mar~h 25, 1969 to Inouy~ et al., 3,461l3~7, l~u~d Augu~t 12, lg69 to Morri~ et 21., 3,75a,011, l~u~d Octob~r 23, 1973 to 6~Yain and 4,~41,094, i~ued Fabruary 3, 1~87 to Dalton, Jr. Thfl ~tate o:~ th~ a~ct ln magnetom~t~r d~ign i~ gurther ~ndi¢ated by Talceuchl ~t al., "A ~esonanl:-Typa Amorphous Ribbon MagnetomQtQ~ Drlven by an Op~rational Ampl~ier, " IEEE T~n~aation~ on ~aanetics, Vol . M~G-20, A~46320/W~H
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No. 5. September 1984, pp 1723-1725.
While the art relating to the design of digital compasses and magnetometers is thus a well-developed one, a need remains for development of a simple, reliable, low cost digital compass suitable for consumer use and a simple magnetometer for detexmining orientation of low intensity magnetic fields.
SUMMARY OF THE INVENTION
Accordingly, it is an object of an aspect of this invention to provide a digital compass which can be imple-mented with a simple digital circuit and which is sufficiently low cost for consumer applications.
It is an object of an aspect of the invention to provide such a digital compass in which orientation with respect to the Earth~s magnetic field is determined by frequency differences obtained with a sensing circuit.
The attainment of these and related objects may be achieved, according to an aspect of this invention, through use of the novel digital compass herein disclosed. A
digital compass in accordance with an aspect of this invention has at least one sensing coil wound on an elongated strip of high direct current permeability magnetic material. The sensing coil is connected to a sensing circuit. The at least one sensing coil and sensing circuit are rssponsive to the Earth's magnetic field to provide an oscillating signal at an output of the sensing circuit which varies in frequency with orientation of the at least one sensing coil with respect to the Earth's magnetic field. A microprocessor is connected to receive in~ormation inputs from the oscillating signal. The microprocessor is configured to convert the information inputs to an indication of the orientation of the at least one sensing coil with respect to the Earth's magnetic field based on the frequency of the oscillating signal. A
display means is connected to receive the orientation indication from the microprocessor.
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The frequency o~ the oscillating signal at the output of the sensing circuit varies substantially, e.g., by about 100 percent, as the sensing coil is moved from a parallel to an antiparallel orientation with respect to the Earth's magnetic field. Such subtantial frequency differences mean that a very accurate digital readout of angle between the sensing coil orientation and magnetic North is obtained from the microprocessor.
Similarly, a magnetometer in accordance with an aspect of the invention has at least one sensing coil wound on an elongated strip of high direct current permeability magnetic material. The sensing coil is connected to a sensing circuitO The at least one sensing coil and sensing circuit are responsive to a magnetic field to provide an oscillating signal at an output of the first sensing circuit which varies in frequency with orientation of the at least one sensing coil with respect to the magnetic field. Tha sensing coil is connected to be self-biased by a direct current through the sensing coil. A means for measuring a frequency of the oscillating signal and providing an indication of the ~requency is connected to receive the oscillating signal.
Other aspects of this invention are as follows:
A magnetometer comprising:
an oscillator circuit comprising:
oscillator driver means having first and second terminals for providing an oscillating current; and sensor means having a first coil wound on a first high permeability isotropic core ~or controlling the frequency of said oscillator circuit, said first coil coupled between said first and second terminals, said first coil having a magnetic axis;
said cscillator driver means for providing a DC bias current through said first coil, such that when said sensor mean~ experiences a rhange in an externally applied - . .
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~;~8~6Z~l -4a-magnetic field, the frequency of the oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said first coil; and measurement means for measuring the frequency of the oscillating current and providing a measurement signal in response thereto.
A digital compass comprising:
a first voltage comparator circuit having first and second input terminals, and an output terminal, said output terminal being coupled back to said second input terminal and said second input terminal being coupled to a first reference potential;
a first sensing coil wound on a high permeability isotropic core having a magnetic axis and being connected between said first input terminal and said output terminal of said first voltage comparator circuit so as to form a first relaxation oscillator, said first relaxation oscillator providing a first oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the first sensing coil; and processor means coupled to receive said oscillating signal from said first relaxation oscillator for providing an indicator signal representative of the orientation of the magnetic axis of said first sensing coil with respect to the direction of the earth's local magnetic field. :
The attainment of khe foregoing and related objects, advantages and ~eatures of the invention should be more readily appare~t to those skilled in the art, after review of the following more detailed description of the invention, taken with the drawings, in which:
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-4b-BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a hysteresis curve for a sensing element used in a digital compass in accordance with the invention.
Figure 2 is a plot useful for understanding operation of the invention.
Figure 3 is a schematic diagram of a sensing circuit used in a digital compass in accordance with the , i "~, '' ' ' '~ ', , ' ~ ' .; ' ', " ' ~
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en~ion.
F~gurQ 4 i8 i!l ~lock diagram o~ a dig~tal oompa~ ~n accordance wit~ th~ in~r~ntion.
DE~AILED ~ESCRIPTION OF T}~ INVENTION
Turning now to th~ drawing~, mor~ particularly lto Figur~ 1, therQ i~ sbown R hyl~tQ~ U~ or a aoD mercially availabl~ METG~ ~norphou~ Alloy ~705M, obtainabl~ ~ro~ Uli~d Signal Corporation. Th~s matarial ol~alt-bas2d magnatia aïloy ~rhich 1~ ~haract~rized by n~ar-z~ro magnetostriction and ~igh DC-p~ ability without annealing. Thl~ materlal is us~d to ~orm ~ o~.
for th~ di~tal compa~ o~ th~ ln~ntlon by w~n~lalg a coil around ~ ~t~aigh~ strip of th~ ~lloy irl a ~r~ditional sol~noid gaometry.
Th~ ~ollowing background ini~orm~tion will :Eaeil~tat~
und~r~tanding o~ th~ inYention. ~or magrl~'clo ~or~
~olenola~, tha iollowing Qquations are g~nerally ~ru~. .
~ QS~
wher~ ~t ie th~ magnetiæin~ ~o~c~, n 1~ the turn d~ 'cy o~
th~ coll in turn~ psr unit l~ngth, ~0 le~ th2 per~abi~ity o~ ~r~ ~pac~, an~ t~ curren'c ~lo~r~ng ln the coil.
. ~ nV ~ (2) wh~r~ E :l~ the potential acro#o ths coil in volt~, n i3 th3 tur~ den~ity ln turn3 per unik l~n~th~ V is th~ voluma o~ th~ ~ora mat~rial, and ~ iB the tim~ d~ri~r~t~e o the tot~l magn~ti~ flux.
Fo:~ ~mall ~an~itlon3 o~ chang~ in ~) th~ aoil can l~e modalad a~ an ideal induator, wh~r~
~5 ~ L a~ (3~
By ~ub~tltution o~ the previou~ e~tauations an~ by ~olvlng, t:he ~ollowinçt can ba shown u ~2 V dH~ t 4 ) wh~re ~ the s~ope o~ thQ B vs. H curve a~ a ~articu~ar p~illt .
~et ~ (H) ~ dH. While moæt magn~ti¢ aor0 ma'c~rial~
A; 4 602 0/WE~
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' ~L289621 ~6-exhibit a con~kant ~ over a laxya rang~ o~ ~, the ~bove METGh~S alloy has uniquely difar~nt aharaoterl~tia~, a~
~hown by the ~tH) plot o~ ~igux~ 2. AB ~hown, by pxovid-lng a dc bia~ current ~hrough the co~l, produ¢lng a magnetizlng ~orc~ Hor th~ coil can ~ bla~d at ~n operat-ing point ~hlch is in the middle ~f sloping r~gion 12 o~
~) cuxve 14. A 6tati¢ magnet~o ~l~ld parall~l to th~
coll will b~ addQd to the Ho and will mov~ the operating polnt in either directlon dependent on t:h~ polarity o~ thQ
~tatla magnetia field. 8inae the indu~tan~a L i8 propor tlonal to ~(~), the lnduct~nce wlll chang~ ap~r~iably wlth the applled 6tatia magnstic ~i~ld.
The abov~ prlnclpl~s of induotlon vaxiA~on ~an b~
ob~er~ed with a relaxation o~clllator 0an~ing a4rcuit 16 u~ing a Sch~itt trig~er 18 ~ ~hown ln Figur~ 3. Th~
perlod o~ th~ ou~put, T, ~ proportion~l to L~R. Th~ ~c bia~ ¢urrent i~ d~pendent on R and the thr~hold l~Vel8 0~
kh~ Schmltt trig~er 18. In general~ by u~lng ~he Ben~or a~ the lnductor timing elemenk o~ any o~cillator aircui~, a chanye in the Btatio f ~ eld wlll produce a frequency chang~ at the QUtpUt. ~he duty cyGl~ should ba a~ym~tri-~al and wlll not vary ~ignifi¢antly with the oper~tlng point ~n the linear r~gion ~(H~, i.Q., the ~lopln~ portlon 12 o~ th~ curve 14 in Figure 2. 6uch a ~sequ~ncy chang~
datoction ~aheme render~ an an~log to digital (A/D) eonver~er unnac~s~ary. No~e that th~ linearity o~ th~
~H~ region i8 not essential to r~aov~r useful informa-tion; the operation r~gion merely ha~ to be monotonlc.
Figure 4 show~ a di~ital compa~ ~0 u~ili2ing a 3en3ing alrcuit 23 o~ the type ~hown in ~igure 3. Th~
compas~ 20 ha~ X, Y and Z ~n~or~ 23, 24 ~nd 2~ ~espea-tlvoly connsoted by line~ 28, 30 and 32 to ~n interPac~
cirault 34. Inter~ce circuit 34 i~ connected to mi¢ro-proce~or 3~ by lin~ 38 . ~he mlcroproc~sr 36 ia aon-nected to a read only memory (ROM) 40 and to ~ r~ndom ACC9~8 memory ~RA~) 42 by lin~s 44 and 46, r~psatively.
Th~ ~icroprocessor 36 i~ conn~cted to a d$~play driv~r 48 A-46 oa O~WEH
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by line 50. Di~play dri~r~r 4~ i~ in ~urn conn~t~d to di~p~y 52 by llne 54.
'rh~ X, Y and Z 813n80rE~ 23, 24 and 26 ~ch have ~hs con~igura~ion 6hown ~or ~he X ~ensor 23. 'rhe X ~an~or ~3 has a Sc~mitt tr~ggar ¢ircuit 56 lmpl~msnted with a ~ 339 typ~ voltage comparatox ~nte~rated circuit, oi~ta$nabl~
from Natlonal Seml~onductor Corporation, Santa Clara, C~llfornla. A ~Vca input is conn~ted through a SOK ohm varlable re~lstor Rl to th~ po~ltiv~ input o~ th2 8chmitt triggQr 56 by lin~ 58. ~ san~or coil 60 having 1200 turn~
o~ wlre around a straight ~trip o~ ~fE~rGLA~ Amorphous Alloy 2705M w~th a length OI 1. 8cm, ~ width o~ O . 5m~ and thlckne~s o~ 20~m 18 connact~d t9 ths negati~re lnpu'c o~
th~ Sohmitt trlgger 56 by lina 62. A t~Vca irlput 1~ o aonn~ct~d through a 5K vari~bla r~stc~r R2 to th~ nega tiv~ lnput o~ Schmitt ~rigg~r 56. Th~ output: c)P th~a 6~h~1tt trigyer 56 i~ connect~ad by ths lin~ 28 to the inter~a~e clrcuit 3 4 . ThQ ~utpu~ o~ t~lB S~h~itt trlgg~r ~ also ~d back on lin~ 64 through the ~en~or coil 60 to the input. Ths output i8 alæo Gonnectsd to *~cc through a lN4148 typs dlod~ Dl, and fed baok on line 6fi throu~h a 4.7K ra~istor R3 to the poait~v0 ~nput o~ tha Bchmi~
trigger 56. ThQ re#l~tor R2 c~n be used to ad~u~t both th~ blao current (and h~n~e th~ op~r~tin~ po~nt) und the ~r~gu4ncy o~ the o~cillator~ Rl wlll chang~ the lo¢atlon o~ the Schmitt trigger's po~itlve and negat~ve thr~sholds.
R3 ~an be u~ed to a~ust the grQgu~ncy and th~ ~urr~nt ~wing o~ the os~llatcr oircuit.
In oper~tlon, ae notad abov~, thQ period r 0~ th~
os~illa~lng output o~ the Schmitt triggar 56 i5 propor-tional to ~/R at th~ input. ~he valu~ o~ ~ varl~s wlth th~ oxisntation o~ th~ ~en~cr co~l S0 wlth respe~t to the Earth'~ magnetia ~ield. Whexa Hs~ ths compon~nt o~ ~h9 ~rth'~ magneti~ ~lald parallel to thq langth o~ thQ
~ansor ~0 and He" 15 taken to b~ po~itlve along th~
dire¢tlon o~ ~0, He" can b~ very ~reci~ely da~rmln~d by d~t~cting ~r0guency d~via~ion. By ha~ng two ~an~or~ in A-46020/WE~
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orthogonal direction~, ~uch a~ x and y, o, th~ oriQntatlon angl2 o~ ths magn~tic No~th with rQ . peag ko th~ ~lxed dir~ction o~ th~ ~ompa~ 20 can b~ d~t~ n~d accordlng to the ~ormula o ~ Arctan ~) By na~ing three s~nsors 23, 24 and ~6, the orl~ntation angl e o~ ~na~netl a North can be determin~d at any f ~ xed dirQction o~ the oompa~s 2 0 in thr~ diman~lon~ . With inalination lnformation, we ~xtract the two compcnente ~e,ly and He"x, which are parallel to the Ear~h'~ ~ur~ace.
In praatioe, an o~cillating ~Qnt~r fr~quency ~0 o~
a~out 200 kH~ is obtain~d with tha sen~or~ 23~ ~4 and 2S.
a ~r~guency changa o~ about 100 % i~ obtainQd aB on~ 0~
the 8~3n80r8 23, 24 and 26 i~ rotatQd ~rom a par~llQl to an antiparall~l direction with r3sp~ct to th~ Earth'~ n~agn~t-ia ~ield . Thi ~ magnltuda oi~ ~rQqu~n~y c:h2nq~3 g~v2s very ~ccurat~a d~gital r~aad out o~ ori~ntation with th~ dlgital co~ a~ 0.
It ~hould now b~ readily apparent to thos~ skill~d in th~ art that A novel diqital co~pas~ capable o~ a¢hleving the stated ob~ect~ o~ kh~ in~sntlon has b~n provided.
Th3 d~gital aompa~s o~ thi3 invention U~8 a ~i~pl~
digltal aircu$t and ia th2r~0r3 o~ su~lc~ently low co~t ~o~ con~umer applications. ThQ compas~ dat~r~ine~ orlon tation with resp~ct to th~ Earth'~ magn~tl~ ld ba~ed on ~gu~n~y dl~erena~s ae the direction o~ a s~nsor changea wlth re~peat to the Eaxth'~ magn~tic ~ield. ~h~ 38n~0r produc~ large enough ~r~u~ncy dl~P~r~nae~ ~o that, d very accurats digltal ro~d o~t o~ ~rien~atlon iB obtained~
It ~hould Purth~r be ~ppar~nt to thos~ ~killQd ln the art that varloue change~ orm and dQtalle oP th~
~nvention a~ ~hown and d~ecribed may b3 made. ~t i~
~n~nded that such change3 b~ included wlth~n the 3pirl~
a~d ~cope o~ th~ claim~ appendQd h~reto.
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patent~ relate gan~rally l:o magnetomot~ros 3,432,751, ~ued March 11, 1969 to Godby Qt al. S 3,435,337, i~uad Mar~h 25, 1969 to Inouy~ et al., 3,461l3~7, l~u~d Augu~t 12, lg69 to Morri~ et 21., 3,75a,011, l~u~d Octob~r 23, 1973 to 6~Yain and 4,~41,094, i~ued Fabruary 3, 1~87 to Dalton, Jr. Thfl ~tate o:~ th~ a~ct ln magnetom~t~r d~ign i~ gurther ~ndi¢ated by Talceuchl ~t al., "A ~esonanl:-Typa Amorphous Ribbon MagnetomQtQ~ Drlven by an Op~rational Ampl~ier, " IEEE T~n~aation~ on ~aanetics, Vol . M~G-20, A~46320/W~H
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No. 5. September 1984, pp 1723-1725.
While the art relating to the design of digital compasses and magnetometers is thus a well-developed one, a need remains for development of a simple, reliable, low cost digital compass suitable for consumer use and a simple magnetometer for detexmining orientation of low intensity magnetic fields.
SUMMARY OF THE INVENTION
Accordingly, it is an object of an aspect of this invention to provide a digital compass which can be imple-mented with a simple digital circuit and which is sufficiently low cost for consumer applications.
It is an object of an aspect of the invention to provide such a digital compass in which orientation with respect to the Earth~s magnetic field is determined by frequency differences obtained with a sensing circuit.
The attainment of these and related objects may be achieved, according to an aspect of this invention, through use of the novel digital compass herein disclosed. A
digital compass in accordance with an aspect of this invention has at least one sensing coil wound on an elongated strip of high direct current permeability magnetic material. The sensing coil is connected to a sensing circuit. The at least one sensing coil and sensing circuit are rssponsive to the Earth's magnetic field to provide an oscillating signal at an output of the sensing circuit which varies in frequency with orientation of the at least one sensing coil with respect to the Earth's magnetic field. A microprocessor is connected to receive in~ormation inputs from the oscillating signal. The microprocessor is configured to convert the information inputs to an indication of the orientation of the at least one sensing coil with respect to the Earth's magnetic field based on the frequency of the oscillating signal. A
display means is connected to receive the orientation indication from the microprocessor.
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The frequency o~ the oscillating signal at the output of the sensing circuit varies substantially, e.g., by about 100 percent, as the sensing coil is moved from a parallel to an antiparallel orientation with respect to the Earth's magnetic field. Such subtantial frequency differences mean that a very accurate digital readout of angle between the sensing coil orientation and magnetic North is obtained from the microprocessor.
Similarly, a magnetometer in accordance with an aspect of the invention has at least one sensing coil wound on an elongated strip of high direct current permeability magnetic material. The sensing coil is connected to a sensing circuitO The at least one sensing coil and sensing circuit are responsive to a magnetic field to provide an oscillating signal at an output of the first sensing circuit which varies in frequency with orientation of the at least one sensing coil with respect to the magnetic field. Tha sensing coil is connected to be self-biased by a direct current through the sensing coil. A means for measuring a frequency of the oscillating signal and providing an indication of the ~requency is connected to receive the oscillating signal.
Other aspects of this invention are as follows:
A magnetometer comprising:
an oscillator circuit comprising:
oscillator driver means having first and second terminals for providing an oscillating current; and sensor means having a first coil wound on a first high permeability isotropic core ~or controlling the frequency of said oscillator circuit, said first coil coupled between said first and second terminals, said first coil having a magnetic axis;
said cscillator driver means for providing a DC bias current through said first coil, such that when said sensor mean~ experiences a rhange in an externally applied - . .
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~;~8~6Z~l -4a-magnetic field, the frequency of the oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said first coil; and measurement means for measuring the frequency of the oscillating current and providing a measurement signal in response thereto.
A digital compass comprising:
a first voltage comparator circuit having first and second input terminals, and an output terminal, said output terminal being coupled back to said second input terminal and said second input terminal being coupled to a first reference potential;
a first sensing coil wound on a high permeability isotropic core having a magnetic axis and being connected between said first input terminal and said output terminal of said first voltage comparator circuit so as to form a first relaxation oscillator, said first relaxation oscillator providing a first oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the first sensing coil; and processor means coupled to receive said oscillating signal from said first relaxation oscillator for providing an indicator signal representative of the orientation of the magnetic axis of said first sensing coil with respect to the direction of the earth's local magnetic field. :
The attainment of khe foregoing and related objects, advantages and ~eatures of the invention should be more readily appare~t to those skilled in the art, after review of the following more detailed description of the invention, taken with the drawings, in which:
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-4b-BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a hysteresis curve for a sensing element used in a digital compass in accordance with the invention.
Figure 2 is a plot useful for understanding operation of the invention.
Figure 3 is a schematic diagram of a sensing circuit used in a digital compass in accordance with the , i "~, '' ' ' '~ ', , ' ~ ' .; ' ', " ' ~
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en~ion.
F~gurQ 4 i8 i!l ~lock diagram o~ a dig~tal oompa~ ~n accordance wit~ th~ in~r~ntion.
DE~AILED ~ESCRIPTION OF T}~ INVENTION
Turning now to th~ drawing~, mor~ particularly lto Figur~ 1, therQ i~ sbown R hyl~tQ~ U~ or a aoD mercially availabl~ METG~ ~norphou~ Alloy ~705M, obtainabl~ ~ro~ Uli~d Signal Corporation. Th~s matarial ol~alt-bas2d magnatia aïloy ~rhich 1~ ~haract~rized by n~ar-z~ro magnetostriction and ~igh DC-p~ ability without annealing. Thl~ materlal is us~d to ~orm ~ o~.
for th~ di~tal compa~ o~ th~ ln~ntlon by w~n~lalg a coil around ~ ~t~aigh~ strip of th~ ~lloy irl a ~r~ditional sol~noid gaometry.
Th~ ~ollowing background ini~orm~tion will :Eaeil~tat~
und~r~tanding o~ th~ inYention. ~or magrl~'clo ~or~
~olenola~, tha iollowing Qquations are g~nerally ~ru~. .
~ QS~
wher~ ~t ie th~ magnetiæin~ ~o~c~, n 1~ the turn d~ 'cy o~
th~ coll in turn~ psr unit l~ngth, ~0 le~ th2 per~abi~ity o~ ~r~ ~pac~, an~ t~ curren'c ~lo~r~ng ln the coil.
. ~ nV ~ (2) wh~r~ E :l~ the potential acro#o ths coil in volt~, n i3 th3 tur~ den~ity ln turn3 per unik l~n~th~ V is th~ voluma o~ th~ ~ora mat~rial, and ~ iB the tim~ d~ri~r~t~e o the tot~l magn~ti~ flux.
Fo:~ ~mall ~an~itlon3 o~ chang~ in ~) th~ aoil can l~e modalad a~ an ideal induator, wh~r~
~5 ~ L a~ (3~
By ~ub~tltution o~ the previou~ e~tauations an~ by ~olvlng, t:he ~ollowinçt can ba shown u ~2 V dH~ t 4 ) wh~re ~ the s~ope o~ thQ B vs. H curve a~ a ~articu~ar p~illt .
~et ~ (H) ~ dH. While moæt magn~ti¢ aor0 ma'c~rial~
A; 4 602 0/WE~
' : - ' .
' ~L289621 ~6-exhibit a con~kant ~ over a laxya rang~ o~ ~, the ~bove METGh~S alloy has uniquely difar~nt aharaoterl~tia~, a~
~hown by the ~tH) plot o~ ~igux~ 2. AB ~hown, by pxovid-lng a dc bia~ current ~hrough the co~l, produ¢lng a magnetizlng ~orc~ Hor th~ coil can ~ bla~d at ~n operat-ing point ~hlch is in the middle ~f sloping r~gion 12 o~
~) cuxve 14. A 6tati¢ magnet~o ~l~ld parall~l to th~
coll will b~ addQd to the Ho and will mov~ the operating polnt in either directlon dependent on t:h~ polarity o~ thQ
~tatla magnetia field. 8inae the indu~tan~a L i8 propor tlonal to ~(~), the lnduct~nce wlll chang~ ap~r~iably wlth the applled 6tatia magnstic ~i~ld.
The abov~ prlnclpl~s of induotlon vaxiA~on ~an b~
ob~er~ed with a relaxation o~clllator 0an~ing a4rcuit 16 u~ing a Sch~itt trig~er 18 ~ ~hown ln Figur~ 3. Th~
perlod o~ th~ ou~put, T, ~ proportion~l to L~R. Th~ ~c bia~ ¢urrent i~ d~pendent on R and the thr~hold l~Vel8 0~
kh~ Schmltt trig~er 18. In general~ by u~lng ~he Ben~or a~ the lnductor timing elemenk o~ any o~cillator aircui~, a chanye in the Btatio f ~ eld wlll produce a frequency chang~ at the QUtpUt. ~he duty cyGl~ should ba a~ym~tri-~al and wlll not vary ~ignifi¢antly with the oper~tlng point ~n the linear r~gion ~(H~, i.Q., the ~lopln~ portlon 12 o~ th~ curve 14 in Figure 2. 6uch a ~sequ~ncy chang~
datoction ~aheme render~ an an~log to digital (A/D) eonver~er unnac~s~ary. No~e that th~ linearity o~ th~
~H~ region i8 not essential to r~aov~r useful informa-tion; the operation r~gion merely ha~ to be monotonlc.
Figure 4 show~ a di~ital compa~ ~0 u~ili2ing a 3en3ing alrcuit 23 o~ the type ~hown in ~igure 3. Th~
compas~ 20 ha~ X, Y and Z ~n~or~ 23, 24 ~nd 2~ ~espea-tlvoly connsoted by line~ 28, 30 and 32 to ~n interPac~
cirault 34. Inter~ce circuit 34 i~ connected to mi¢ro-proce~or 3~ by lin~ 38 . ~he mlcroproc~sr 36 ia aon-nected to a read only memory (ROM) 40 and to ~ r~ndom ACC9~8 memory ~RA~) 42 by lin~s 44 and 46, r~psatively.
Th~ ~icroprocessor 36 i~ conn~cted to a d$~play driv~r 48 A-46 oa O~WEH
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by line 50. Di~play dri~r~r 4~ i~ in ~urn conn~t~d to di~p~y 52 by llne 54.
'rh~ X, Y and Z 813n80rE~ 23, 24 and 26 ~ch have ~hs con~igura~ion 6hown ~or ~he X ~ensor 23. 'rhe X ~an~or ~3 has a Sc~mitt tr~ggar ¢ircuit 56 lmpl~msnted with a ~ 339 typ~ voltage comparatox ~nte~rated circuit, oi~ta$nabl~
from Natlonal Seml~onductor Corporation, Santa Clara, C~llfornla. A ~Vca input is conn~ted through a SOK ohm varlable re~lstor Rl to th~ po~ltiv~ input o~ th2 8chmitt triggQr 56 by lin~ 58. ~ san~or coil 60 having 1200 turn~
o~ wlre around a straight ~trip o~ ~fE~rGLA~ Amorphous Alloy 2705M w~th a length OI 1. 8cm, ~ width o~ O . 5m~ and thlckne~s o~ 20~m 18 connact~d t9 ths negati~re lnpu'c o~
th~ Sohmitt trlgger 56 by lina 62. A t~Vca irlput 1~ o aonn~ct~d through a 5K vari~bla r~stc~r R2 to th~ nega tiv~ lnput o~ Schmitt ~rigg~r 56. Th~ output: c)P th~a 6~h~1tt trigyer 56 i~ connect~ad by ths lin~ 28 to the inter~a~e clrcuit 3 4 . ThQ ~utpu~ o~ t~lB S~h~itt trlgg~r ~ also ~d back on lin~ 64 through the ~en~or coil 60 to the input. Ths output i8 alæo Gonnectsd to *~cc through a lN4148 typs dlod~ Dl, and fed baok on line 6fi throu~h a 4.7K ra~istor R3 to the poait~v0 ~nput o~ tha Bchmi~
trigger 56. ThQ re#l~tor R2 c~n be used to ad~u~t both th~ blao current (and h~n~e th~ op~r~tin~ po~nt) und the ~r~gu4ncy o~ the o~cillator~ Rl wlll chang~ the lo¢atlon o~ the Schmitt trigger's po~itlve and negat~ve thr~sholds.
R3 ~an be u~ed to a~ust the grQgu~ncy and th~ ~urr~nt ~wing o~ the os~llatcr oircuit.
In oper~tlon, ae notad abov~, thQ period r 0~ th~
os~illa~lng output o~ the Schmitt triggar 56 i5 propor-tional to ~/R at th~ input. ~he valu~ o~ ~ varl~s wlth th~ oxisntation o~ th~ ~en~cr co~l S0 wlth respe~t to the Earth'~ magnetia ~ield. Whexa Hs~ ths compon~nt o~ ~h9 ~rth'~ magneti~ ~lald parallel to thq langth o~ thQ
~ansor ~0 and He" 15 taken to b~ po~itlve along th~
dire¢tlon o~ ~0, He" can b~ very ~reci~ely da~rmln~d by d~t~cting ~r0guency d~via~ion. By ha~ng two ~an~or~ in A-46020/WE~
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orthogonal direction~, ~uch a~ x and y, o, th~ oriQntatlon angl2 o~ ths magn~tic No~th with rQ . peag ko th~ ~lxed dir~ction o~ th~ ~ompa~ 20 can b~ d~t~ n~d accordlng to the ~ormula o ~ Arctan ~) By na~ing three s~nsors 23, 24 and ~6, the orl~ntation angl e o~ ~na~netl a North can be determin~d at any f ~ xed dirQction o~ the oompa~s 2 0 in thr~ diman~lon~ . With inalination lnformation, we ~xtract the two compcnente ~e,ly and He"x, which are parallel to the Ear~h'~ ~ur~ace.
In praatioe, an o~cillating ~Qnt~r fr~quency ~0 o~
a~out 200 kH~ is obtain~d with tha sen~or~ 23~ ~4 and 2S.
a ~r~guency changa o~ about 100 % i~ obtainQd aB on~ 0~
the 8~3n80r8 23, 24 and 26 i~ rotatQd ~rom a par~llQl to an antiparall~l direction with r3sp~ct to th~ Earth'~ n~agn~t-ia ~ield . Thi ~ magnltuda oi~ ~rQqu~n~y c:h2nq~3 g~v2s very ~ccurat~a d~gital r~aad out o~ ori~ntation with th~ dlgital co~ a~ 0.
It ~hould now b~ readily apparent to thos~ skill~d in th~ art that A novel diqital co~pas~ capable o~ a¢hleving the stated ob~ect~ o~ kh~ in~sntlon has b~n provided.
Th3 d~gital aompa~s o~ thi3 invention U~8 a ~i~pl~
digltal aircu$t and ia th2r~0r3 o~ su~lc~ently low co~t ~o~ con~umer applications. ThQ compas~ dat~r~ine~ orlon tation with resp~ct to th~ Earth'~ magn~tl~ ld ba~ed on ~gu~n~y dl~erena~s ae the direction o~ a s~nsor changea wlth re~peat to the Eaxth'~ magn~tic ~ield. ~h~ 38n~0r produc~ large enough ~r~u~ncy dl~P~r~nae~ ~o that, d very accurats digltal ro~d o~t o~ ~rien~atlon iB obtained~
It ~hould Purth~r be ~ppar~nt to thos~ ~killQd ln the art that varloue change~ orm and dQtalle oP th~
~nvention a~ ~hown and d~ecribed may b3 made. ~t i~
~n~nded that such change3 b~ included wlth~n the 3pirl~
a~d ~cope o~ th~ claim~ appendQd h~reto.
~-~60~0~W~
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Claims (17)
1. A magnetometer comprising:
an oscillator circuit comprising:
oscillator driver means having first and second terminals for providing an oscillating current; and sensor means having a first coil wound on a first high permeability isotropic core for controlling the frequency of said oscillator circuit, said first coil coupled between said first and second terminals, said first coil having a magnetic axis;
said oscillator driver means for providing a DC bias current through said first coil, such that when said sensor means experiences a change in an externally applied magnetic field, the frequency of the oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said first coil; and measurement means for measuring the frequency of the oscillating current and providing a measurement signal in response thereto.
an oscillator circuit comprising:
oscillator driver means having first and second terminals for providing an oscillating current; and sensor means having a first coil wound on a first high permeability isotropic core for controlling the frequency of said oscillator circuit, said first coil coupled between said first and second terminals, said first coil having a magnetic axis;
said oscillator driver means for providing a DC bias current through said first coil, such that when said sensor means experiences a change in an externally applied magnetic field, the frequency of the oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said first coil; and measurement means for measuring the frequency of the oscillating current and providing a measurement signal in response thereto.
2. A magnetometer as in claim 1 wherein said oscillator drive means includes resistive means connected between a source of an electric potential and said sensor means for providing said DC bias current.
3. A magnetometer as in claim 1 wherein said measurement means comprises microprocessor means for providing said measurement signal such that said measurement signal is functionally related to the magnitude and sign of the externally applied magnetic field.
4. A magnetometer as in claim 3 further comprising display means coupled to receive said measurement signal from said microprocessor means for displaying a representation of the magnitude and sign of the externally applied magnetic field relative to the magnetic axis of said first coil.
5. A magnetometer as in claim 1 further comprising:
a second oscillator circuit comprising:
second oscillator driver means having first and second terminals for providing a second oscillating current; and second sensor means having a second coil wound on a second high permeability isotropic core for controlling the frequency of said second oscillator circuit, said second coil coupled between said first and second terminals of said second oscillator driver means, said second coil having a magnetic axis with a directional component othogonal to the magnetic axis of the first coil;
said second oscillator driver means for providing a DC
bias current through said second coil, such that when said second sensor means experiences a change in the externally applied magnetic field, the frequency of the second oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said second coil; and wherein said measurement means includes means for measuring the frequency of the second oscillating current and providing a second measurement signal in response thereto.
a second oscillator circuit comprising:
second oscillator driver means having first and second terminals for providing a second oscillating current; and second sensor means having a second coil wound on a second high permeability isotropic core for controlling the frequency of said second oscillator circuit, said second coil coupled between said first and second terminals of said second oscillator driver means, said second coil having a magnetic axis with a directional component othogonal to the magnetic axis of the first coil;
said second oscillator driver means for providing a DC
bias current through said second coil, such that when said second sensor means experiences a change in the externally applied magnetic field, the frequency of the second oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said second coil; and wherein said measurement means includes means for measuring the frequency of the second oscillating current and providing a second measurement signal in response thereto.
6. A magnetometer as in claim 5 further comprising:
a third oscillator circuit comprising:
third oscillator driver means having first and second terminals for providing a third oscillating current; and third sensor means having a third coil wound on a third high permeability isotropic core for controlling the frequency of said third oscillator circuit, said third coil coupled between said first and second terminals of said third oscillator driver means, said third coil having a magnetic axis with a directional component orthogonal to the magnetic axis of the first coil and the magnetic axis of the second coil;
said third oscillator driver means for providing a DC
bias current through said third coil, such that when said third sensor means experiences a change in the externally applied magnetic field, the frequency of the third oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said third coil; and wherein said measurement means includes means for measuring the frequency of the third oscillating current and providing a third measurement signal in response thereto.
a third oscillator circuit comprising:
third oscillator driver means having first and second terminals for providing a third oscillating current; and third sensor means having a third coil wound on a third high permeability isotropic core for controlling the frequency of said third oscillator circuit, said third coil coupled between said first and second terminals of said third oscillator driver means, said third coil having a magnetic axis with a directional component orthogonal to the magnetic axis of the first coil and the magnetic axis of the second coil;
said third oscillator driver means for providing a DC
bias current through said third coil, such that when said third sensor means experiences a change in the externally applied magnetic field, the frequency of the third oscillating current changes monotonically with the change in magnitude of the applied external magnetic field in the direction of the magnetic axis of said third coil; and wherein said measurement means includes means for measuring the frequency of the third oscillating current and providing a third measurement signal in response thereto.
7. A magnetometer as in claim 1 wherein said high permeability material is a metallic glass alloy.
8. A magnetometer as in claim 6 wherein said first, second and third oscillator drivers comprise Schmitt trigger circuits.
9. A digital compass comprising:
a first voltage comparator circuit having first and second input terminals, and an output terminal, said output terminal being coupled back to said second input terminal and said second input terminal being coupled to a first reference potential;
a first sensing coil wound on a high permeability isotropic core having a magnetic axis and being connected between said first input terminal and said output terminal of said first voltage comparator circuit so as to form a first relaxation oscillator, said first relaxation oscillator providing a first oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the first sensing coil; and processor means coupled to receive said oscillating signal from said first relaxation oscillator for providing an indicator signal representative of the orientation of the magnetic axis of said first sensing coil with respect to the direction of the earth's local magnetic field.
a first voltage comparator circuit having first and second input terminals, and an output terminal, said output terminal being coupled back to said second input terminal and said second input terminal being coupled to a first reference potential;
a first sensing coil wound on a high permeability isotropic core having a magnetic axis and being connected between said first input terminal and said output terminal of said first voltage comparator circuit so as to form a first relaxation oscillator, said first relaxation oscillator providing a first oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the first sensing coil; and processor means coupled to receive said oscillating signal from said first relaxation oscillator for providing an indicator signal representative of the orientation of the magnetic axis of said first sensing coil with respect to the direction of the earth's local magnetic field.
10. A digital compass as in claim 9 further comprising display means coupled to receive said indicator signal for displaying a signal related to the relative orientation of said first sensing coil with respect to the direction of the earth's local magnetic field.
11. A digital compass of claim 9 wherein:
said magnetic axis of said first sensing coil is the X
axis; said digital compass further comprises:
a second voltage comparator circuit having first and second input terminals, and an output terminal, with the second input therminal being connected to a second reference potential;
a second sensing coil wound on a high permeability isotropic core having a magnetic axis, the Y axis, that is orthogonal to the X axis, said second sensing coil being connected between said first input terminal and said output terminal of said second relaxation oscillator, said second relaxation oscillator providing a second oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the second sensing coil;
a third voltage comparator circuit having first and second input terminals, and an output terminal, with the second input terminal being connected to a third reference potential; and a third sensing coil wound on a high permeability isotrophic core having a magnetic axis, the Z axis, that is orthogonal to both the X and Y axes, said third sensing coil being connected between said first input terminal and said output terminal of said third voltage comparator circuit so as to form a third relaxation oscillator, said
said magnetic axis of said first sensing coil is the X
axis; said digital compass further comprises:
a second voltage comparator circuit having first and second input terminals, and an output terminal, with the second input therminal being connected to a second reference potential;
a second sensing coil wound on a high permeability isotropic core having a magnetic axis, the Y axis, that is orthogonal to the X axis, said second sensing coil being connected between said first input terminal and said output terminal of said second relaxation oscillator, said second relaxation oscillator providing a second oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the second sensing coil;
a third voltage comparator circuit having first and second input terminals, and an output terminal, with the second input terminal being connected to a third reference potential; and a third sensing coil wound on a high permeability isotrophic core having a magnetic axis, the Z axis, that is orthogonal to both the X and Y axes, said third sensing coil being connected between said first input terminal and said output terminal of said third voltage comparator circuit so as to form a third relaxation oscillator, said
12 third relaxation oscillator providing a third oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the third sensing coil;
and said processor means further coupled to receive said oscillating signals from said second and third relaxation oscillators for providing indicator signals representative of the orientation of the magnetic axis of said second and third sensing coils with respect to the direction of the earth's local magnetic field.
12. The digital compass of claim 11 wherein at least one of said first, second, and third voltage comparator circuits is a Schmitt trigger circuit.
and said processor means further coupled to receive said oscillating signals from said second and third relaxation oscillators for providing indicator signals representative of the orientation of the magnetic axis of said second and third sensing coils with respect to the direction of the earth's local magnetic field.
12. The digital compass of claim 11 wherein at least one of said first, second, and third voltage comparator circuits is a Schmitt trigger circuit.
13. A digital compass of claim 9 wherein said high permeability material is a metallic glass alloy.
14. A digital compass comprising the magnetometer of claim 6 and wherein said applied external magnetic field is the earth's magnetic field.
15. The digital compass of claim 9 wherein:
said magnetic axis of said first sensing coil is the X axis, said digital compass further comprising:
a second voltage comparator circuit having first and second input terminals, and an output terminal, said output terminal of said second voltage comparator circuit being coupled back to said second input terminal of said second voltage comparator circuit;
a second sensing coil having a magnetic axis, the Y
axis, that is orthogonal to the X axis, said second sensing coil being connected between said first input terminal and said output terminal of said second voltage comparator circuit so as to form a second relaxation oscillator, said second relaxation oscillator providing a second oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the second sensing coil;
and said processor means further coupled to receive said second oscillating signal from said second relaxation oscillator for providing an indicator signal representative of the orientation of the magnetic axis of said second sensing coil with respect to the direction of the earth's local magnetic field.
said magnetic axis of said first sensing coil is the X axis, said digital compass further comprising:
a second voltage comparator circuit having first and second input terminals, and an output terminal, said output terminal of said second voltage comparator circuit being coupled back to said second input terminal of said second voltage comparator circuit;
a second sensing coil having a magnetic axis, the Y
axis, that is orthogonal to the X axis, said second sensing coil being connected between said first input terminal and said output terminal of said second voltage comparator circuit so as to form a second relaxation oscillator, said second relaxation oscillator providing a second oscillating signal having a frequency that is a monotonic function of the magnitude of the earth's local magnetic field in the direction of the magnetic axis of the second sensing coil;
and said processor means further coupled to receive said second oscillating signal from said second relaxation oscillator for providing an indicator signal representative of the orientation of the magnetic axis of said second sensing coil with respect to the direction of the earth's local magnetic field.
16. The digital compass of claim 15 wherein at least one of said first and second voltage comparator circuits is a Schmitt trigger circuit.
17. The digital compass of claim 15 wherein said high permeability cores are constructed of a metallic glass alloy.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/069,495 US4851775A (en) | 1987-07-02 | 1987-07-02 | Digital compass and magnetometer having a sensor coil wound on a high permeability isotropic core |
| US069,495 | 1993-06-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1289621C true CA1289621C (en) | 1991-09-24 |
Family
ID=22089373
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000570993A Expired - Lifetime CA1289621C (en) | 1987-07-02 | 1988-06-30 | Frequency difference digital compass and magnetometer |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4851775A (en) |
| EP (1) | EP0376977B1 (en) |
| JP (1) | JP2934446B2 (en) |
| AT (1) | ATE134773T1 (en) |
| AU (1) | AU603529B2 (en) |
| CA (1) | CA1289621C (en) |
| DE (1) | DE3855048T2 (en) |
| FI (1) | FI896339A0 (en) |
| WO (1) | WO1989000297A1 (en) |
Families Citing this family (60)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5329269A (en) * | 1990-08-10 | 1994-07-12 | Watson William S | Single core triaxial flux-gate magnetometer |
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-
1987
- 1987-07-02 US US07/069,495 patent/US4851775A/en not_active Expired - Lifetime
-
1988
- 1988-06-30 WO PCT/US1988/002191 patent/WO1989000297A1/en active IP Right Grant
- 1988-06-30 AU AU23190/88A patent/AU603529B2/en not_active Expired
- 1988-06-30 DE DE3855048T patent/DE3855048T2/en not_active Expired - Lifetime
- 1988-06-30 JP JP63507091A patent/JP2934446B2/en not_active Expired - Lifetime
- 1988-06-30 AT AT88908050T patent/ATE134773T1/en not_active IP Right Cessation
- 1988-06-30 CA CA000570993A patent/CA1289621C/en not_active Expired - Lifetime
- 1988-06-30 EP EP88908050A patent/EP0376977B1/en not_active Expired - Lifetime
-
1989
- 1989-12-29 FI FI896339A patent/FI896339A0/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0376977A1 (en) | 1990-07-11 |
| DE3855048D1 (en) | 1996-04-04 |
| WO1989000297A1 (en) | 1989-01-12 |
| JP2934446B2 (en) | 1999-08-16 |
| DE3855048T2 (en) | 1996-10-24 |
| EP0376977A4 (en) | 1991-07-17 |
| AU603529B2 (en) | 1990-11-15 |
| AU2319088A (en) | 1989-01-30 |
| JPH02504072A (en) | 1990-11-22 |
| EP0376977B1 (en) | 1996-02-28 |
| ATE134773T1 (en) | 1996-03-15 |
| FI896339A0 (en) | 1989-12-29 |
| US4851775A (en) | 1989-07-25 |
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