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
  • G01R33/04—Measuring direction or magnitude of magnetic fields or magnetic flux using the flux-gate principle

Definitions

• the present invention relates to a Low Power Flux-gate Magnetometer for
• Flux-gate Magnetometers are well known in the art. Such devices measure the
• inductor is driven by an alternating current signal having, for example, a sinusoidal or
• the AC input current induces an alternating magnetic field within
• the input signal has sufficient amplitude such that the induced current
• the magnetic flux density within the flux-gate core is a function of both the
• Prior art flux-gate magnetometers are constant amplitude, alternating current
• the series resistance is selected to be many times larger
• the current through the circuit is determined mainly by the resistor rather than
• the input to the flux-gate coil is also connected to
• the voltage across the flux-gate inductor generally follows the inductor current
• the magnetometer circuit is driven by a
• flux-gate magnetometers are very favorable, especially when compared to Hall effect and
• the magnetometer is a constant current device
• the magnetometer is to be battery powered, the current consumption of the device must be battery powered
• magnetometers including linearity, accuracy and noise immunity, while simultaneously
• Another object of the present invention is to provide a magnetometer having a
• An additional of object of the present invention is to provide a flux-gate magnetometer wherein the flux-gate inductor is driven by a relatively low frequency AC
• Yet another object of the present invention is to provide a magnetometer which
• Still another object of the present invention is to provide a flux-gate
• the Flux-Gate Magnetometer of the present invention measures external
• the input square wave generates a sinusoidal current signal through the flux-gate
• a capacitor is connected between the flux-gate output and
• the comparator is configured as a logic gate which changes states when the voltage across
• the capacitor reaches l A the amplitude of the input voltage signal.
• the output signal from the comparator is related to the input signal, but the timing
• Logic circuitry is provided to compare the comparator output signal to the input
• the logic circuitry generates two pulse width modulated
• the pulse width of the first PWM signal pulses corresponds to the rising edge
• Pulse width demodulating circuitry is provided to measure the difference in pulse
• the demodulation circuitry includes
• the magnetometer of the present invention draws much less current than
• the invention is also particularly well suited to magnetostrictive torque sensing
• the invention is ideal for portable consumer products which require torque sensing or any combination
• FIG. 1 is a schematic diagram of a Micro-Power Magnetometer circuitry
• FIG. 2 shows pulse width modulated output signals from NOR gates 116, 118
• FIG. 1 depicted in FIG. 1;
• FIG. 2a shows the two signals when no external magnetic field is present
• FIG. 2b shows the two signals when an external magnetic field is present
• FIG. 2c show the two signals when an external magnetic field is present
• the present invention relates to a flux-gate magnetometer, and more particularly
• Micro-Power Flux-Gate Magnetometer circuitry is
• magnetometer circuit 100 The significant elements of magnetometer circuit 100 include an inverting circuit
• inverter 114 first and second NOR gates 116, 118; first and second analog switches 120,
• the flux-gate inductor 104 is positioned near the point where external
• the flux-gate coil 104 is oriented such that the
• the input to the magnetometer circuit 100 is excited by a
• Input buffer 102 inverts the input
• the output of buffer 102 drives the
• flux-gate inductor 104 and one input of the first NOR gate 116, and the output of flux-
• first Schotky diode 108 is also connected between the flux-gate inductor 104 output and
• the output of second output inverter 114 drives the second input of second NOR gate
• first NOR gate 116 drives the first analog switch 120, and the
• the two analog switches 120, 122 are configured to operate as a tri-state switch.
• the first analog switch 120 is referenced to the supply voltage V DD , and second analog
• switch 122 is referenced to ground.
• the outputs of the two analog switches 120, 122, are
• a low pass filter comprising 10K ⁇ resistor 124 and
• This symmetrical square wave voltage signal alternates
• Flux-gate inductor 104 is constructed with a
• the threshold saturation current I SAT which saturates the flux-gate core is
• buffer 112 connected to the output of flux-gate 104 and capacitor 106 operates as a
• buffer 112 will be set to logic 1(V DD ) when the voltage across capacitor 105 is less than
• Schottky diodes 108, 110 are
• capacitor 106 will begin resonantly charging from O.OV toward V DD .
• the rate at which capacitor 106 begins charging will be
• capacitor 106 is less than V_V DD , the output of inverting output buffer 112 is set to logic
• capacitor 106 charges to V DD
• capacitor 106 down to O.OV almost immediately. As the voltage on capacitor 106 drops
• Capacitor 106 is sized such that during the discharge cycle, the saturation current I SAT occurs when the voltage across capacitor 106 is approximately
• inverting output buffer 112 is connected directly to one
• output buffer 112 In addition to one input of NOR gate 116, output buffer 112 also drives second
• Inverter 114 applies the inverted output of buffer 112 to one input
• magnetometer circuitry 100 is applied to the other input of NOR gate 118.
• NOR gate 118 NOR gate 118
• each pulse output from NOR gate 118 corresponds to the time delay
• gates 116, 118 corresponds to the propagation delay of both the rising and falling edges
• circuit 100 is inverted prior to being input to the flux-gate, a forward current is induced
• capacitor 106 begins charging when the input signal transitions from V DD to OV.
• the external magnetic field is oriented such that the
• Capacitor 106 begins discharging when the input
• FIG. 2b shows the same output pulse trains
• FIG. 2b the external field is oriented in a
• FIG. 2c shows the output
• NOR gates 116 and 118 are of equal width. In FIG. 2b, however, the forward
• FIG. 2c shows the
• NOR gate 116 is much narrower than the wider output pulses from NOR gate 118.
• outputs of NOR gates 116, 118 are in effect pulse width modulated signals where the
• pulse width of the two signals is determined by the strength and direction of the external magnetic field.
• the low pass filter comprising the lOk ⁇ resistor 124 and the O.Ol ⁇ F capacitor 126.
• Switch 120 is input to analog switch 122.
• Switch 120 is referenced to the supply voltage V DD , and
• switch 122 is referenced to ground. The outputs of the two switches are connected
• switch 120 act as a tri-state switch.
• switch 120 When the input to switch 120 is high, switch 120
• V DD is input to the low pass filter.
• switch 122 is high, switch 122 becomes conductive, and ground potential is applied to the filter.
• capacitor 126 will begin charging toward V DD .
• capacitor 126 will begin discharging
• Capacitor 126 and resistor 124 are sized such that the RC time constant
• switch 120 will be conductive for
• pulses output from NOR gate 116 are of greater duration than those output from NOR
• analog switch 120 is conductive for each cycle of the input waveform.
• capacitor 126 spends slightly more
• magnetic field is oriented in a second direction, 180E opposite the first direction
• analog switch 122 is conductive for a longer duration than analog
• analog switches 120, 122 will be conductive for a greater and greater amount of time
• This analog signal can be used to drive a conventional volt meter, or some other
• the circuit shown in FIG. 1 consumes only a fraction of the power consumed by
• capacitor 1 to changing the frequency of the input waveform.
• capacitor 2 In the preferred embodiment capacitor

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• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Measuring Magnetic Variables (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Cited By (2)

Families Citing this family (5)

Citations (1)

• 1998
  • 1998-02-24 US US09/028,858 patent/US6014025A/en not_active Expired - Lifetime
• 1999
  • 1999-01-25 AU AU23384/99A patent/AU2338499A/en not_active Abandoned
  • 1999-01-25 JP JP2000533768A patent/JP4409765B2/ja not_active Expired - Lifetime
  • 1999-01-25 GB GB0020648A patent/GB2349956B/en not_active Expired - Fee Related
  • 1999-01-25 DE DE19982981T patent/DE19982981T1/de not_active Ceased
  • 1999-01-25 WO PCT/US1999/001441 patent/WO1999044072A1/en not_active Ceased
  • 1999-02-24 TW TW088102622A patent/TW509800B/zh not_active IP Right Cessation

Patent Citations (1)

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