RU2686519C1 - Digital ferro-probe magnetometer - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to electric measuring equipment and can be used for measurement of three orthogonal components of magnetic field induction vector. Digital ferroprobe magnetometer contains a digital-to-analogue converter, to which a current amplifier is connected, which is connected to three ferro-probes. Each ferro-probe is connected through normalizing amplifier to three-channel analog-to-digital converter, which is connected to microcontroller, which is connected to digital-to-analogue converter.

EFFECT: high accuracy of measuring three orthogonal components of the magnetic field induction vector, high measurement speed and reliability of operation.

1 cl, 1 dwg

Description

The invention relates to the field of electrical engineering and can be used to measure the three orthogonal components of the magnetic induction vector.

Known digital fluxgate magnetometer [RU 2316781 C1, IPC G01R 33/02, publ. 10.02.2008], containing a master oscillator, a sinusoid shaper, the output of which is connected to the first inputs of flux-probes, whose outputs are connected to the inputs of selective amplifiers, digital-to-analog converters, logic unit and sampling-storage devices, the first inputs of which are connected to the outputs of selective amplifiers, the first outputs connected to the first inputs of analog-to-digital converters, the second outputs are connected to the second inputs of flux-probes. The first output of the logic control unit is connected to the input of the power source, the second output is connected to the second inputs of the sample-hold devices, the third output is connected to the second inputs of the analog-to-digital converters. The input of the logic control unit is connected to the output of the master oscillator. Each channel of the magnetometer is covered by a deep negative feedback on the magnetic field.

This device provides low accuracy and measurement speed of the components of the magnetic field induction vector, has structural complexity and, therefore, low reliability of operation.

Known digital fluxgate magnetometer [RU 2503025 C2, IPC G01R 33/02 (2006.01), publ. 27.12.2013] containing a master oscillator, the output of which is connected to the input of the logic unit, the output of which is connected to the input of a sinusoid shaper, the output of which is connected to the first inputs of three flux-probes, the outputs of which are connected to the inputs of three selective amplifiers, the outputs of which are connected to the inputs of three devices sample storage, the first outputs of which are connected to the second inputs of the three flux-probes. The inputs of the three multiplexers and three inverters are connected to the third outputs of the three sample-hold devices, and the outputs are connected to the second inputs of three multiplexers, the first inputs of which are connected to the second outputs of the three sample-storage devices, and the outputs are connected to the inputs of three analog-digital converters.

To isolate the voltage of the second harmonic from the total spectrum of the signal coming from the measuring windings of flux-probes, selective amplifiers with a finite odd harmonic suppression factor and a resonance frequency different from the second harmonic frequency were used, which reduces the measurement accuracy due to errors in their element base.

The closest adopted for the prototype, is a digital fluxgate magnetometer [RU 2455656 C1, IPC G01R 33/02 (2006.01), publ. 10.07.2012] containing a selective amplifier, the output of which is connected to the first input of the sampling-storage device, the second input of which is connected to the third output of the logic control unit, and the first output is connected to the first input of the analog-to-digital converter, the second input of which is connected to the fourth output a logical control unit, the input of which is connected to the output of the master oscillator, and the first output is connected to the input of the sinusoid shaper, the output of which is connected to the first inputs of the flux-probes, three registers and a multiplex Corso, the first input of which is connected to the output of the first fluxgate, the second input is connected to the output of the second fluxgate, the third input is connected to the output of the third fluxgate, the fourth input is connected to the second output of the sampling-storage device, the first output is connected to the second input of the first fluxgate, the second output is connected with the second input of the second fluxgate, the third output is connected to the second input of the third fluxgate, the fourth output is connected to the input of the selective amplifier, the fifth input is connected to the second output of the logic control unit The fifth output is connected to the second input of the first register, the sixth output is connected to the second input of the second register, the seventh output is connected to the second input of the third register, the first input of which is connected to the first inputs of the first and second registers and the output of the analog-digital converter.

This device has a low measurement rate due to the use of a multiplexer. In addition, the use of a selective amplifier with a finite coefficient of suppression of odd harmonics and with a resonance frequency different from the frequency of the second harmonic for extracting the voltage of the second harmonic from the overall signal spectrum provides low accuracy of measurements due to errors in the element base of the selective amplifier.

The technical result of the proposed invention is to increase the measurement accuracy of the three orthogonal components of the magnetic field induction vector, increase the measurement speed and reliability.

Digital fluxgate magnetometer, as well as in the prototype, contains three fluxgate and analog-to-digital converter.

According to the invention, a current amplifier is connected to a digital-to-analog converter, which is connected to three flux-probes, each of which is connected to a three-channel analog-to-digital converter through a normalizing amplifier, which is connected to a microcontroller that is connected to a digital-to-analog converter.

The proposed digital flux-gate magnetometer makes it possible to excite flux-probes with a complex signal containing in its spectrum the first three odd harmonics of equal amplitude, realize measurements of the instantaneous voltages from the outputs of the flux-probes, and use the principle of synchronous detection for the first three even harmonics to increase the accuracy of measurements of the induction vector components magnetic field and increase the speed of measurements. The use of a digital-analog converter, a three-channel analog-digital converter and a microcontroller allowed us to simplify the circuit, which increased the reliability of the device.

Figure 1 shows the block diagram of the digital fluxgate magnetometer.

Digital fluxgate magnetometer contains a digital-to-analog converter 1 (DAC), to the output of which current amplifier 2 (UT) is connected, which is connected to the inputs of the first 3 (ФЗ1), second 4 (ФЗ2) and third 5 (ФЗ3) ferrozond. The output of the first fluxgate 3 (ФЗ1) is connected via the first normalizing amplifier 6 (NU1) to the first input of the analog-digital converter 7 (ADC). The output of the second fluxgate 4 (FZ2) is connected via the second normalizing amplifier 8 (NU2) to the second input of the analog-to-digital converter 7 (ADC). The output of the third flux-gate 5 (ФЗ3) is connected to the third input of the analog-to-digital converter 7 (ADC) via the third normalizing amplifier 9 (LSD). Analog-to-digital converter 7 (ADC) is connected via an interface to a microcontroller 10 (MC), which is connected via an interface to a digital-to-analog converter 1 (DAC).

As a digital-to-analog converter 1 (DAC) any 14-bit digital-analog converter with a sampling frequency of at least 100 times the excitation frequency of the fluxgate 3 (FZ1), 4 (FZ2), 5 (FZ3) can be used. The current amplifier 2 (UT) can be implemented according to a typical emitter-follower voltage circuit. As the flux-gates 3 (FZ1), 4 (FZ2), 5 (FZ3), any differential flux-gate transducers can be used, for example Mag-01H. The normalizing amplifiers 6 (NU1), 8 (NU2), 9 (NUZ) can be implemented on any operational amplifiers with programmable gain, for example, PGA207. As an analog-to-digital converter 7 (ADC), any three-channel 14-bit analog-to-digital converter with differential inputs with a sampling frequency of not less than 100 times the excitation frequency of flux probes 3 (FZ1), 4 (FZ2), 5 can be used. (FZ3). Any 32-bit microcontroller 10 (MK) can be used, for example, AT32UC3A0512.

Digital fluxgate magnetometer works as follows. The microcontroller 10 (MK) through the interface sets the output parameters of the digital-to-analog converter 1 (DAC): voltage amplitude, voltage frequency, waveform. At the output of the digital-to-analog converter 1 (DAC) after the current amplifier 2 (UT), the signal has the form:

U (t) = Usin [(ω + 3ω + 5ω) t],

Where

U is the amplitude, V;

ω - frequency, rad / s;

t - time, s.

This signal is fed to the excitation windings of the fluxgate 3 (FZ1), 4 (FZ2), 5 (FZ3). Ferrosonde 3 (ФЗ1), 4 (ФЗ2), 5 (ФЗ3) convert the external signal acting on them (the projection of the magnetic field induction vector on their longitudinal axes) into AC voltages U _Ф1 (t), U _Ф2 {t), U _Ф3 (t) respectively, containing the even harmonics of the frequency of the excitation signal 2ω, 4ω, 6ω. The amplitudes of even harmonics in these voltages are proportional to the value of the magnetic field induction, and the phase changes by 180 ° when the direction of the field induction vector is changed by 180 °. In the voltages U _F1 (t), U _F2 (t), U _F3 (t) there is also an interference corresponding to odd harmonics. The signals from the outputs of flux-probes 3 (FZ1), 4 (FZ2), 5 (FZ3) are amplified by normalizing amplifiers 6 (NU1), 8 (NU2), 9 (NUZ), respectively, digitized by the analog-digital converter 7 (ADC) and transmitted via the interface into the microcontroller 10 (MK). In the microcontroller 10 (MK), each digitized voltage U _Фl (t), U _Ф2 (t), U _Ф3 {t) is multiplied by digital sequences that implement the following analog signals:

U _c1 (t) = U ₀ sin (2ωt);

U _c2 (t) = U ₀ sin (4ωt);

U _c3 (t) = U ₀ sin (6ωt).

Thereby implementing the principle of synchronous detection of even harmonics from the 1st to the 3rd. As a result of multiplication for each voltage U _Ф1 (t), U _Ф2 (t), U _Ф3 (t), at phase frequency ω = 0, three common-mode components are obtained, which are proportional to even harmonics from 1 to 3. For each voltage U _Фl (t), U _Ф2 (t), U _Ф3 (t), the in-phase components are summed by the microcontroller. The result of the summation is proportional to the corresponding component of the magnetic field induction vector.

Claims (1)

Digital fluxgate magnetometer containing three fluxgate and analog-to-digital converter, characterized in that a current amplifier is connected to the digital-to-analog converter, which is connected to three flux-probes, each of which is connected to a three-channel analog-digital converter that is connected to a microcontroller which is connected to a digital-to-analog converter.

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