Magnetic sensor control system and method

Abstract

The application provides a kind of magnetic sensor control system and method, belong to magnetic sensor technical field, magnetic sensor control system includes magnetic sensor, atomic gas chamber temperature control circuit, laser temperature control circuit and laser current control circuit, atomic gas chamber temperature control circuit controls the temperature of atomic gas chamber based on negative feedback closed loop control algorithm, laser current control circuit controls the temperature of laser based on the light absorption characteristic curve of atomic gas chamber, laser current control circuit adjusts the drive voltage of the laser based on voltage negative feedback closed loop control algorithm to realize the closed loop control of the drive current of the laser, realize the cooperative control of magnetic sensor, accurately control atomic gas chamber temperature, laser temperature and current, avoid affecting fine magnetic signal measurement.

Description

Technical Field

[0001] This invention relates to the field of magnetic sensor technology, and in particular to a magnetic sensor control system and method. Background Technology

[0002] In recent years, optically pumped magnetometers (OPMs) have attracted widespread attention due to their superior performance in measuring extremely weak magnetic fields. These magnetic sensors operate in near-zero magnetic field environments, exhibiting excellent magnetic field sensitivity, which is of great significance for monitoring magnetic fields related to the human body. Magnetic field signals generated by human activity mainly originate from two sources: one is from muscle activity, such as cardiac magnetocardiography (MCC) and myogenic signals, which can be detected by magnetocardiography (MCA) and magnetomyography (MGM) systems, respectively; the other is generated by neural activity, such as brain magnetic signals, which can be detected by magnetoencephalography (MEG). Therefore, OPMs are widely used in various biomedical fields, including magnetocardiography, MGM, and MEG.

[0003] To meet the growing demand for biomagnetic detection applications in the biomedical field, optically pumped magnetometer sensors are being developed towards miniaturization, leading to the emergence of single-beam OPM sensors. Single-beam OPM sensors use vertical-cavity surface-emitting lasers (VCSELs) as the key light source, and their stability is easily affected by temperature and current fluctuations, which affects the actual effect of fine magnetic signal measurement. Therefore, it is necessary to propose a control system to ensure that the single-beam OPM sensor is in the best working condition. Summary of the Invention

[0004] This invention provides a magnetic sensor control system and method, which solves the problem that the stability of VCSEL lasers in the prior art is easily affected by temperature and current fluctuations, thus affecting the actual effect of fine magnetic signal measurement.

[0005] This invention provides a magnetic sensor control system, including a magnetic sensor, an atomic gas chamber temperature control circuit, a laser temperature control circuit, and a laser current control circuit;

[0006] The atomic gas chamber temperature control circuit is used to heat the atomic gas chamber of the magnetic sensor to a preset value, and then heat the atomic gas chamber based on a negative feedback closed-loop control algorithm so that the temperature of the atomic gas chamber is at the set value, wherein the preset value is less than the set value.

[0007] The laser temperature control circuit is used to heat the laser of the magnetic sensor until the light absorption characteristic curve of the atomic gas cell is obtained, and to cool the laser based on the light absorption characteristic curve until the output voltage of the magnetic sensor reaches the preset stable frequency voltage value.

[0008] The laser current control circuit is used to adjust the driving voltage of the laser based on a voltage negative feedback closed-loop control algorithm after the output voltage of the magnetic sensor reaches a preset stable frequency voltage value, so as to realize closed-loop control of the driving current of the laser.

[0009] As one embodiment, the magnetic sensor control system includes a core controller;

[0010] The atomic chamber temperature control circuit includes an atomic chamber temperature measuring circuit and an atomic chamber heating circuit, which are electrically connected to the core controller, respectively.

[0011] The laser temperature control circuit includes a laser temperature measurement circuit and a laser heating circuit, which are electrically connected to the core controller, respectively.

[0012] As an example, the operating frequencies of the heating drive signals of the atomic gas chamber heating circuit and the laser heating circuit are different from the optimal operating frequency of the magnetic sensor.

[0013] As one embodiment, both the atomic gas chamber heating circuit and the laser heating circuit include a gain amplification circuit, a heating filter circuit, a voltage and power amplification circuit, and a heating element connected in sequence.

[0014] The gain amplifier circuit is used to amplify the input heating drive signal to the gain factor set by the core controller.

[0015] The heating filter circuit is used to filter out the DC component of the amplified heating drive signal;

[0016] The voltage and power amplifier circuit is used to amplify the voltage and power of the filtered heating drive signal to drive the heating element.

[0017] As one embodiment, both the atomic gas chamber temperature measurement circuit and the laser temperature measurement circuit include a temperature detection element, a differential amplifier circuit, a voltage amplifier circuit, and a temperature measurement filter circuit connected in sequence.

[0018] The differential amplifier circuit is used to differentially amplify the voltage signal corresponding to the temperature detection element to obtain a differential voltage signal;

[0019] The voltage amplifier circuit is used to amplify the differential voltage signal.

[0020] The temperature measurement and filtering circuit is used to filter out high-frequency noise in the differential voltage signal after voltage amplification and output it to the core controller. The core controller is used to determine the respective heating drive signals of the atomic gas chamber heating circuit and the laser heating circuit based on the received signal.

[0021] As one embodiment, the laser current control circuit includes a laser driving circuit, which includes a differential amplifier, a reference resistor, and a negative feedback circuit. The output terminal of the differential amplifier is connected to the reference resistor and the negative feedback circuit, respectively.

[0022] The differential amplifier is used to adjust the voltage difference across the reference resistor based on the negative feedback signal input to the negative feedback circuit so that the current in the reference resistor remains constant.

[0023] The present invention also provides a magnetic sensor control method, implemented based on the aforementioned magnetic sensor control system, comprising:

[0024] After heating the atomic gas chamber of the magnetic sensor to a preset value, the atomic gas chamber is heated based on a negative feedback closed-loop control algorithm so that the temperature of the atomic gas chamber is at a set value, where the preset value is less than the set value.

[0025] The laser of the magnetic sensor is heated until the light absorption characteristic curve of the atomic gas cell is obtained. Based on the light absorption characteristic curve, the laser is cooled until the output voltage of the magnetic sensor reaches the preset stable frequency voltage value.

[0026] After the output voltage of the magnetic sensor reaches the preset stable frequency voltage value, the driving voltage of the laser is adjusted based on the voltage negative feedback closed-loop control algorithm to achieve closed-loop control of the driving current of the laser.

[0027] As one embodiment, heating the atomic gas chamber based on the negative feedback closed-loop control algorithm to bring the temperature of the atomic gas chamber to a set value includes:

[0028] The atomic gas chamber is heated based on a negative feedback closed-loop control algorithm, and it is determined whether the temperature fluctuation range of the atomic gas chamber is within a first preset range.

[0029] If the temperature fluctuation range of the atomic gas chamber is not within the first preset range, the parameters of the negative feedback closed-loop control algorithm are adjusted, and the atomic gas chamber is heated based on the adjusted negative feedback closed-loop control algorithm until the temperature fluctuation range of the atomic gas chamber is within the second preset range.

[0030] Wherein, the first preset range covers the second preset range.

[0031] As one embodiment, before heating the atomic gas cell of the magnetic sensor to a preset value, the method further includes:

[0032] The atomic gas chamber is heated in an open-loop manner based on the maximum power, and the negative feedback closed-loop control algorithm is activated.

[0033] As one embodiment, cooling the laser based on the light absorption characteristic curve until the output voltage of the magnetic sensor reaches a preset frequency-stabilized voltage value includes:

[0034] The temperature value of the lowest voltage point of the light absorption characteristic curve is superimposed with a temperature compensation coefficient to determine the target temperature for open-loop cooling of the laser.

[0035] The laser is subjected to open-loop cooling until its temperature reaches the target temperature.

[0036] Reduce the power of open-loop cooling so that the output voltage of the magnetic sensor reaches the preset stable frequency voltage value.

[0037] The magnetic sensor control system and method provided by this invention include an atomic gas chamber temperature control circuit that controls the temperature of the atomic gas chamber based on a negative feedback closed-loop control algorithm, a laser current control circuit that controls the laser temperature based on the light absorption characteristic curve of the atomic gas chamber, and a laser current control circuit that adjusts the driving voltage of the laser based on a voltage negative feedback closed-loop control algorithm to achieve closed-loop control of the driving current of the laser. This enables coordinated control of the magnetic sensor, precisely controlling the atomic gas chamber temperature, laser temperature, and current, and avoiding interference with the measurement of refined magnetic signals. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 This is one of the structural schematic diagrams of the magnetic sensor control system provided by the present invention.

[0040] Figure 2 This is a schematic diagram of an embodiment of the magnetic sensor provided by the present invention.

[0041] Figure 3 This is the second schematic diagram of the magnetic sensor control system provided by the present invention.

[0042] Figure 4 This is a circuit diagram of the atomic gas chamber heating circuit provided by the present invention.

[0043] Figure 5 This is a circuit diagram of the atomic gas chamber temperature measurement circuit provided by the present invention.

[0044] Figure 6 This is a circuit diagram of the laser driving circuit provided by the present invention.

[0045] Figure 7 This is one of the flowcharts illustrating the magnetic sensor control method provided by the present invention.

[0046] Figure 8 This is the second flowchart of the magnetic sensor control method provided by the present invention.

[0047] Figure 9 This is a schematic diagram of the atomic gas chamber temperature control process provided by the present invention.

[0048] Figure 10 This is a schematic diagram of the laser temperature and current control process provided by the present invention.

[0049] Figure 11 This is a schematic diagram comparing the temperature measurement curve provided by the present invention with the actual temperature measurement value.

[0050] Figure 12 This is a schematic diagram comparing the measured and calculated output values ​​of the laser driver circuit provided by the present invention.

[0051] Figure 13 This is a schematic diagram of the temperature curve of the atomic gas chamber provided by the present invention.

[0052] Figure 14 This is a schematic diagram of the temperature curve of the laser provided by the present invention.

[0053] In the diagram: 100 - Magnetic sensor, 200 - Atomic gas chamber temperature control circuit, 210 - Atomic gas chamber heating circuit, 211 - Heating element, 212 - Gain amplifier circuit, 213 - Heating filter circuit, 214 - Voltage and power amplifier circuit, 220 - Atomic gas chamber temperature measurement circuit, 221 - Differential amplifier circuit, 222 - Voltage amplifier circuit, 223 - Temperature measurement filter circuit, 300 - Laser temperature control circuit, 400 - Laser current control circuit. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0055] Figure 1 This is one of the structural schematic diagrams of the magnetic sensor control system provided by the present invention, such as... Figure 1 As shown, the present invention provides a magnetic sensor control system, including a magnetic sensor 100, an atomic gas chamber temperature control circuit 200, a laser temperature control circuit 300, and a laser current control circuit 400.

[0056] The atomic gas chamber temperature control circuit 200 is used to heat the atomic gas chamber of the magnetic sensor 100 to a preset value, and then heat the atomic gas chamber based on a negative feedback closed-loop control algorithm so that the temperature of the atomic gas chamber is at a set value, wherein the preset value is less than the set value.

[0057] The laser temperature control circuit 300 is used to heat the laser of the magnetic sensor 100 until the light absorption characteristic curve of the atomic gas cell is obtained, and to cool the laser based on the light absorption characteristic curve until the output voltage of the magnetic sensor 100 reaches the preset stable frequency voltage value.

[0058] The laser current control circuit 400 is used to adjust the driving voltage of the laser based on a voltage negative feedback closed-loop control algorithm after the output voltage of the magnetic sensor 100 reaches a preset stable frequency voltage value, so as to realize closed-loop control of the driving current of the laser.

[0059] Optionally, the magnetic sensor 100 of the present invention is a sensor used in the measurement of biomagnetic signals. The embodiments of the present invention are illustrated using an optically pumped magnetometer as an example.

[0060] like Figure 2 As shown, the magnetic sensor 100 in this embodiment of the invention is a compact single-beam laser OPM sensor. The single beam serves as both the pump light and the probe light, satisfying the functional requirements of pumping and probing within a smaller space. The vertical-cavity surface-emitting laser of the OPM sensor generates a laser with a wavelength λ of 795nm. After being collimated by a lens (Fluorite Crystal, FC), the laser passes sequentially through a λ / 4 waveplate and an 87Rb atomic gas cell. The optical signal output from the atomic gas cell is converted into a voltage signal by a photodiode (PD) to determine the output voltage of the magnetic sensor 100. Preferably, the dimensions of the OPM sensor are length × width × height = 41mm × 20mm × 20mm.

[0061] After heating the atomic gas chamber of the magnetic sensor 100 to a preset value, specifically, after initiating the atomic gas chamber heating process, the atomic gas chamber of the magnetic sensor 100 is heated in an open-loop manner to the preset value. Open-loop heating means that during the heating process, the heating process is not adjusted based on feedback signals, and the heating power or heating time is not adjusted according to actual temperature feedback. The preset value refers to the optimal operating temperature of the atomic gas chamber. The preset value can be determined as a percentage of the set value, for example, the preset value can be set to 90%-95% of the set value, preferably 95%.

[0062] The laser of the magnetic sensor 100 is heated until the light absorption characteristic curve of the atomic gas cell is obtained. Specifically, this means performing a temperature sweep operation on the laser, gradually heating the laser until the light absorption characteristic curve of the atomic gas cell appears. The light absorption characteristic curve serves as the basis for cooling the laser.

[0063] After the output voltage of the magnetic sensor 100 reaches the preset stable frequency voltage value, the driving voltage of the laser is kept constant based on the voltage negative feedback closed-loop control algorithm, thereby ensuring the constant driving current of the laser. The present invention adopts the voltage negative feedback closed-loop control algorithm because the voltage output of the photodiode can directly reflect the degree of light absorption by the atomic gas cell, and can directly determine the frequency stability and achieve better control.

[0064] During the operation of the OPM sensor, it is necessary to control the current and temperature of the VCSEL laser and the temperature of the atomic gas chamber to ensure normal sensor operation. While maintaining a constant VCSEL drive current, controlling the VCSEL laser temperature ensures that it outputs laser light at a wavelength of 795nm. Given the extreme temperature sensitivity of the VCSEL laser, deviations in temperature can prevent it from producing the required wavelength. Therefore, it is also necessary to control the temperature of the atomic gas chamber to ensure that the vapor density of 87Rb atoms within the chamber reaches an appropriate level. Excessive temperature reduces the sensor bandwidth, while excessively low temperature reduces sensor sensitivity. This invention employs three control circuits for coordinated control, precisely controlling the VCSEL laser temperature. These three integrated control circuits play a decisive role in the parameter control of the OPM sensor, enabling closed-loop control of the laser, atomic gas chamber temperature parameters, and laser drive current parameters within the OPM.

[0065] Understandably, the atomic gas chamber temperature control circuit 200 controls the temperature of the atomic gas chamber based on a negative feedback closed-loop control algorithm, the laser current control circuit 400 controls the laser temperature based on the light absorption characteristic curve of the atomic gas chamber, and the laser current control circuit 400 adjusts the driving voltage of the laser based on a voltage negative feedback closed-loop control algorithm to achieve closed-loop control of the driving current of the laser, thereby achieving coordinated control of the magnetic sensor 100, accurately controlling the atomic gas chamber temperature, laser temperature and current, and avoiding affecting the fine magnetic signal measurement.

[0066] Based on the above embodiments, as an optional embodiment, the magnetic sensor control system includes a core controller.

[0067] The atomic chamber temperature control circuit 200 includes an atomic chamber temperature measuring circuit 220 and an atomic chamber heating circuit 210, which are electrically connected to the core controller, respectively.

[0068] The laser temperature control circuit 300 includes a laser temperature measurement circuit and a laser heating circuit, which are electrically connected to the core controller, respectively.

[0069] Optionally, the magnetic sensor control system can use a single controller to control the atomic gas chamber temperature control circuit 200, the laser temperature control circuit 300, and the laser current control circuit 400 respectively. Alternatively, separate controllers can be set in the atomic gas chamber temperature control circuit 200, the laser temperature control circuit 300, and the laser current control circuit 400. This embodiment of the invention uses a single core controller as an example for illustration. The core controller can be composed of a single-chip microcomputer. In this embodiment of the invention, an STM32 single-chip microcomputer is used as an example for illustration.

[0070] The core controller is composed of an STM32F103RCT6 microcontroller, which is responsible for monitoring the operating status of the OPM sensor and executing processes such as current driving, temperature monitoring, gain control and heating driving to maintain the stable working state of the sensor.

[0071] Current drive: The STM32F103RCT6 microcontroller controls the digital-to-analog converter (DAC) AD5541 to output the laser drive voltage, which is then converted into current to drive the VCSEL laser.

[0072] Temperature monitoring: The ADS1256 analog-to-digital converter (ADC) is used to acquire the voltage values ​​generated by the temperature monitoring circuit of the atomic gas cell and laser diode.

[0073] Gain control: The voltage value controlling the amplification factor of the Variable Gain Amplifier (VGA) AD8337 is calculated. The Direct Digital Synthesizer (DDS) AD9837 circuit generates a 50kHz heating-driven sine wave. This frequency is much higher than the bandwidth range of the OPM sensor, which can effectively filter out the sine wave in the signal processing circuit, ensuring signal quality.

[0074] Heating Drive: The driving sine wave passes through the atomic gas chamber heating circuit 210 and the VCSEL laser heating circuit.

[0075] The magnetic sensor control system is integrated into a circuit board, which includes a top plate and a bottom plate. The top plate has excellent heat dissipation capabilities to prevent overheating and triggering the overheat protection of the OPA552FA chip. The bottom plate communicates with the host computer via a serial-to-USB interface to transmit parameters. Real-time temperature monitoring data from the atomic gas chamber and VCSEL laser, as well as information from the transimpedance amplifier circuit, are sent to the host computer for real-time monitoring of the OPM sensor's operating status.

[0076] Optionally, the operating frequencies of the heating drive signals of the atomic gas chamber heating circuit 210 and the laser heating circuit are different from the optimal operating frequency of the magnetic sensor 100.

[0077] In the performance specifications of OPM sensors, they typically exhibit high detection sensitivity within a 100Hz frequency bandwidth. If the frequency of the heating drive current used in the atomic gas chamber and VCSEL laser is set to a bandwidth less than or near 100Hz, it will interfere with the measured magnetic field signal. Considering the limitations of the power amplifier gain-bandwidth product (GBP) parameter, to achieve higher power output, this invention sets the operating frequency of the heating drive signals of the atomic gas chamber heating circuit 210 and the laser heating circuit to 50kHz.

[0078] Based on the above embodiments, as an optional embodiment, both the atomic gas chamber heating circuit 210 and the laser heating circuit include a gain amplification circuit 212, a heating filter circuit 213, a voltage and power amplification circuit 214, and a heating element 211 connected in sequence.

[0079] The gain amplifier circuit 212 is used to amplify the input heating drive signal to the gain factor set by the core controller.

[0080] The heating filter circuit 213 is used to filter out the DC component of the amplified heating drive signal.

[0081] The voltage and power amplifier circuit 214 is used to amplify the voltage and power of the filtered heating drive signal to drive the heating element 211.

[0082] The atomic gas chamber heating circuit 210 and the laser heating circuit have the same circuit structure. This embodiment of the invention will be described using the atomic gas chamber heating circuit 210 as an example.

[0083] like Figure 4 As shown, the heating drive signal of the atomic gas chamber heating circuit 210, with a frequency set to 50kHz, is input to the AD8337 chip through a buffer follower. The AD8337 is a high-precision VGA whose internal architecture can be simplified to a combination of an operational amplifier and a gain adjustment module. The internal operational amplifier of this chip is responsible for the primary amplification of the input signal; the gain adjustment module is responsible for adjusting the gain of the amplified output signal. Since the output signal of the AD8337 chip contains a DC component, it needs to be input to a Sallen-Key high-pass filter to filter out the DC component before further signal amplification. The signal processed by the Sallen-Key high-pass filter first passes through a passive high-pass filter, and then is input to a non-inverting amplifier to amplify the voltage signal. Finally, the signal is sent to the power amplifier OPA552FA for further power amplification. The OPA552FA chip has a maximum current output capability of 380mA and a bandwidth of 12MHz, ensuring that it can provide sufficient power output to the heating element 211 to meet the heating requirements.

[0084] The gain of the atomic gas chamber heating circuit 210 can be calculated using the characteristics of the chip and operational amplifier. for:

[0085] (1)

[0086] in, This is the controlled gain factor for VGA. , , , , , The values ​​shown in the diagram represent the resistance values ​​of the resistors. When the input heating drive control voltage is within the range of -0.6V to 0.6V, the gain factor exhibits an approximately linear trend. (Resistance value of the ceramic heating element.) At around 55 Ω, when the voltage amplitude of the heating drive wave is Effective heating power for:

[0087] (2)

[0088] By adjusting the heating power by changing the gain factor, the temperature of the alkali metal atom gas chamber and the VCSEL laser is maintained, thereby enabling control of the sensor.

[0089] It is understood that the variable gain circuit, heating and filtering circuit 213, and voltage and power amplification circuit 214 designed based on the AD8337 chip and OPA552 chip constitute the atomic gas chamber heating circuit 210 and the laser heating circuit. This invention can achieve approximately linear gain adjustment within a specific voltage input range, as well as DC component filtering function, while also ensuring the power requirements of the downstream heating components.

[0090] Based on the above embodiments, as an optional embodiment, both the atomic gas chamber temperature measurement circuit 220 and the laser temperature measurement circuit include a temperature detection element, a differential amplifier circuit 221, a voltage amplifier circuit 222, and a temperature measurement filter circuit 223 connected in sequence. The temperature detection element is composed of a thermistor.

[0091] The differential amplifier circuit 221 is used to differentially amplify the voltage signal corresponding to the temperature detection element to obtain a differential voltage signal.

[0092] The voltage amplifier circuit 222 is used to amplify the differential voltage signal.

[0093] The temperature measurement and filtering circuit 223 is used to filter out high-frequency noise in the differential voltage signal after voltage amplification and output it to the core controller. The core controller is used to determine the respective heating drive signals of the atomic gas chamber heating circuit 210 and the laser heating circuit based on the received signal.

[0094] The atomic gas chamber temperature measuring circuit 220 and the laser temperature measuring circuit have the same circuit structure. This embodiment of the invention will be described using the atomic gas chamber temperature measuring circuit 220 as an example.

[0095] like Figure 5 As shown, taking a PT1000 resistor as the temperature sensing element as an example, the PT1000 was chosen primarily because of its excellent linear response characteristics, meaning there is a linear relationship between the PT1000 resistance value and temperature changes. Under standard conditions at 0 °C, the PT1000 resistance is calibrated to 1 kΩ, and it increases with increasing temperature. Using a Wheatstone bridge circuit, the resistance change of the PT1000 can be converted into a voltage change between the bridge output terminals, so that... Figure 3 The ADC in the system can perform effective data acquisition.

[0096] To ensure stable operation of the bridge circuit and reduce electromagnetic interference caused by excessive current, the atomic gas chamber temperature measurement circuit 220 employs a voltage divider structure to reduce the driving voltage to 60 mV. The bridge's driving voltage is provided by a stable 2 V DC reference voltage from the ADR4520 chip. The voltage signal output by the bridge is fed into a low-noise precision instrumentation amplifier AD8429 for differential amplification. The amplified differential signal is further adjusted by a non-inverting amplifier to achieve a voltage level suitable for ADC acquisition. Subsequently, the signal is fed into a Sallen-Key low-pass filter to remove high-frequency noise components. The cutoff frequency of the Sallen-Key low-pass filter is set to 35 Hz, effectively eliminating high-frequency AC noise interference that may affect the effective DC signal.

[0097] The relationship between the output voltage of the atomic gas chamber temperature measuring circuit 220 and the resistance value of PT1000 can be calculated based on the properties of the operational amplifier and the characteristics of the chip:

[0098] (3)

[0099] in, The magnification of AD8429. To connect the bridge voltage of the bridge circuit, This refers to the resistance value of the PT1000 resistor. This is the output voltage of the temperature measuring circuit.

[0100] After establishing the relationship between the output voltage of the atomic gas chamber temperature measuring circuit 220 and the resistance value of PT1000, it is also necessary to establish the relationship between the resistance value of PT1000 and the temperature, specifically:

[0101] (4)

[0102] in ℃ -1 , ℃ -2 . For temperature, The standard resistance measured by the PT1000 temperature sensor at 0°C is 1 kΩ. Because... Therefore, in Temperature range of ℃ The relationship between the resistance of PT1000 and temperature can be approximated as linear.

[0103] Formula (4) can be simplified to the following formula:

[0104] (5)

[0105] During circuit parameter debugging, the thermal characteristics differences between the laser heating circuit and the atomic gas chamber heating system circuit must be precisely considered. These thermal characteristics refer to the different target temperatures of the laser and the atomic gas chamber. For the laser, although the required operating temperature is relatively low, temperature has a significant impact on the stability and accuracy of its output wavelength.

[0106] It is understood that the present invention is based on the AD8429 chip and designs an adjustable full-bridge differential circuit, a voltage amplifier circuit 222, and a temperature measurement and filtering circuit 223, which can simultaneously realize the functions of accurate detection of analog voltage, DC component filtering, and accurate amplification of voltage data of the PT1000 module.

[0107] Based on the above embodiments, as an optional embodiment, the laser current control circuit 400 includes a laser driving circuit, which includes a differential amplifier, a reference resistor, and a negative feedback circuit. The output terminal of the differential amplifier is connected to the reference resistor and the negative feedback circuit, respectively.

[0108] The differential amplifier is used to adjust the voltage difference across the reference resistor based on the negative feedback signal input to the negative feedback circuit so that the current in the reference resistor remains constant.

[0109] The output wavelength of a VCSEL laser depends on temperature and current. By keeping the VCSEL laser drive current constant and precisely controlling its temperature, the output wavelength of the laser can be precisely controlled.

[0110] like Figure 6 As shown, the main structure of the AD8276 differential amplifier can be simplified to a combination of resistors and operational amplifiers. The basic principle is to use a negative feedback structure to control the reference resistor. The voltage difference across the two ends, thereby maintaining the flow. The current is kept constant to maintain the stability of the VCSEL laser input current. Because... It has a significant impact on current stability, so a precision metal foil resistor of model RJ711 was specially selected as the reference resistor. This resistor has an accuracy of up to 0.01% and a temperature coefficient as low as 5ppm.

[0111] Let the voltage of the AD5541 input circuit be... The current through the VCSEL laser is Then we can get:

[0112] (6)

[0113] because ,therefore:

[0114] (7)

[0115] Within the current output range of the AD8276 differential amplifier, the current across the load varies with the input voltage. The laser driver circuit can only drive a laser diode with a current of up to 1.6mA, while the AD8276 can provide a maximum current output of 15mA, meeting the driving requirements of the laser diode.

[0116] It is understood that the present invention builds a voltage-controlled current laser driving circuit based on a negative feedback structure, which can realize the function of precise control of the driving current of VCSEL laser diode module.

[0117] The magnetic sensor control method provided by the present invention is described below. The magnetic sensor control method described below can be referred to in correspondence with the magnetic sensor control system described above.

[0118] like Figure 7 As shown, the present invention also provides a magnetic sensor control method, which is implemented based on the magnetic sensor control system and includes the following steps.

[0119] Step S100: After heating the atomic gas chamber of the magnetic sensor to a preset value, the atomic gas chamber is heated based on a negative feedback closed-loop control algorithm so that the temperature of the atomic gas chamber is at a set value, wherein the preset value is less than the set value.

[0120] Step S200: Heat the laser of the magnetic sensor until the light absorption characteristic curve of the atomic gas cell is obtained, and cool the laser based on the light absorption characteristic curve until the output voltage of the magnetic sensor reaches the preset stable frequency voltage value.

[0121] Step S300: After the output voltage of the magnetic sensor reaches the preset stable frequency voltage value, the driving voltage of the laser is adjusted based on the voltage negative feedback closed-loop control algorithm to achieve closed-loop control of the driving current of the laser.

[0122] like Figure 8 As shown, to enhance the magnetic field detection capability of the sensor, it is essential to ensure that a sufficient number of 87Rb atoms participate in the optical pumping phenomenon within the alkali metal atomic gas chamber. This requires precise temperature control of the atomic gas chamber to accelerate the thermal motion of the 87Rb atoms. When a sufficient number of 87Rb atoms participate in the optical pumping, the absorption of the laser light generated by the VCSEL laser within the atomic gas chamber is enhanced, providing a basis for subsequent temperature scanning of the optical absorption characteristics.

[0123] The VCSEL laser has a drive current of 1.4 mA and outputs a center wavelength of 795 nm when the temperature is maintained at approximately 77°C. Considering the laser's temperature drift rate of 0.055 nm / K, assuming a drive current supplied to the laser at a room temperature of 25°C, the center wavelength of the laser output will be approximately 792.4 nm. To ensure the 87Rb atoms are in an optically pumped state, the laser wavelength interacting with the 87Rb atoms should be 795 nm. If optical pumping does not occur, the laser will almost completely pass through the atomic gas cell and be captured by the photodiode, which will generate a large current, causing the sensor output to saturate. When the atomic gas cell temperature is maintained at an appropriate value, the VCSEL laser heating program should be initiated, gradually increasing the temperature to gradually increase the center wavelength of the laser output, eventually exceeding 795 nm. Temperature feedback control can be applied to reduce the temperature over a wide range and stabilize it at a temperature slightly above the 795 nm resonant point. Subsequently, an open-loop method was used to reduce the heating power within a small range, fine-tuning the temperature and output wavelength so that the photodiode output gradually approached the set stable point as the VCSEL laser temperature decreased. Finally, the feedback voltage was determined based on the current flowing through the photodiode, allowing for fine-tuning of the laser temperature within a small range.

[0124] Based on the above embodiments, as an optional embodiment, heating the atomic gas chamber based on the negative feedback closed-loop control algorithm to bring the temperature of the atomic gas chamber to a set value includes:

[0125] The atomic gas chamber is heated based on a negative feedback closed-loop control algorithm, and it is determined whether the temperature fluctuation range of the atomic gas chamber is within a first preset range.

[0126] If the temperature fluctuation range of the atomic gas chamber is not within the first preset range, the parameters of the negative feedback closed-loop control algorithm are adjusted, and the atomic gas chamber is heated based on the adjusted negative feedback closed-loop control algorithm until the temperature fluctuation range of the atomic gas chamber is within the second preset range.

[0127] Wherein, the first preset range covers the second preset range.

[0128] Optionally, before heating the atomic gas cell of the magnetic sensor to a preset value, the method further includes:

[0129] The atomic gas chamber is heated in an open-loop manner based on the maximum power, and the negative feedback closed-loop control algorithm is activated.

[0130] After starting the atomic gas chamber heating process, open-loop heating is first performed at maximum power while PID calculation is started simultaneously. This can prevent the temperature drop caused by the PID control program starting from the lowest power when switching from open-loop heating at maximum power to PID negative feedback heating.

[0131] like Figure 9 As shown, after heating the atomic gas chamber to 95% of the set value, a negative feedback closed-loop control algorithm (PID negative feedback control algorithm) is used to gradually stabilize the atomic gas chamber temperature at the set value. If the atomic gas chamber temperature fluctuates slightly around the set value (temperature measurement voltage fluctuation within the first preset range of 0.01V), the PID parameters should be adjusted to reduce the proportional gain and eliminate the derivative gain to improve the stability of temperature control around the set value. Once the atomic gas chamber temperature stabilizes (temperature measurement voltage fluctuation within the second preset range of 0.005V), the VCSEL laser heating is activated, and the laser output wavelength is controlled.

[0132] As one embodiment, cooling the laser based on the light absorption characteristic curve until the output voltage of the magnetic sensor reaches a preset frequency-stabilized voltage value includes:

[0133] The temperature value of the lowest voltage point of the light absorption characteristic curve is superimposed with a temperature compensation coefficient to determine the target temperature for open-loop cooling of the laser.

[0134] The laser is subjected to open-loop cooling until its temperature reaches the target temperature.

[0135] Reduce the power of open-loop cooling so that the output voltage of the magnetic sensor reaches the preset stable frequency voltage value.

[0136] like Figure 10 As shown, the laser of this invention ensures a stable output frequency by changing the temperature while maintaining a constant driving current. Before starting the control process, a constant current of 1.4mA should be input to the VCSEL laser to output laser power at its rated level. After the control process starts, a temperature sweep operation is first performed, gradually heating the VCSEL laser until the light absorption characteristic curve of the atomic gas cell (i.e., the temperature sweep curve in the figure) appears. The voltage reference point for frequency stabilization is determined based on the light absorption characteristic curve. At the same time, the temperature value corresponding to the lowest voltage point on the light absorption characteristic curve is recorded. Due to the heat conduction time introduced by the PT1000 temperature sensor, there is a lag in the detection of temperature changes. The temperature value of the lowest voltage point cannot be directly used as the target stable temperature. A compensation coefficient needs to be added to obtain a temperature value slightly higher than the lowest voltage point of the temperature sweep curve. The compensated temperature value is used as the basis for temperature negative feedback PID control.

[0137] The temperature negative feedback PID algorithm can rapidly reduce the heating power, causing the VCSEL laser temperature to gradually decrease. Once the temperature approaches the set value, open-loop control further reduces the heating power for fine-tuning of the temperature. The open-loop cooling process is very short. During the gradual temperature reduction, the voltage output of the PT1000 temperature sensor can be observed to gradually decrease, eventually approaching the set stable frequency voltage point. Once near the set stable frequency voltage point, voltage is used as feedback for PID control. The voltage directly reflects the degree of light absorption by the atomic gas cell, allowing for direct assessment of frequency stability and better control.

[0138] When the voltage negative feedback control is initiated, the area around the VCSEL laser has reached thermal equilibrium, thus preventing large-scale fluctuations in heating power. To reduce the impact of accidental disturbances, the control program can employ an averaging method for the output power control quantity. The control expression is as follows:

[0139] (8)

[0140] in, The output power of the heating control at the current moment. For the front i The output power of the heating control is constantly monitored. For voltage negative feedback, the proportional gain For integral gain, and The number of points used for averaging, i.e., the average number of samples during averaging, is used; the larger the number, the more accurate the result. In this embodiment of the invention... N The characteristic value is 100. Stable operation of the OPM sensor can be ensured by continuously applying voltage negative feedback PID control.

[0141] The technical effects of the present invention will be described below with reference to the accompanying drawings.

[0142] like Figure 11 As shown, the yellow curve represents the theoretical curve for laser temperature measurement, and the purple curve represents the theoretical curve for gas chamber temperature measurement. This invention uses a precisely calibrated standard resistor as the circuit input to acquire the corresponding output voltage. Plotting the obtained experimental data as curves in a graph allows observation of the consistency between the experimental results and theoretical predictions.

[0143] like Figure 12 As shown, the measured value of the output of the VCSEL laser drive circuit is basically consistent with the calculated value, proving that the present invention can achieve high-precision current output.

[0144] like Figure 13As shown, this invention outputs the temperature data of the atomic gas chamber in real time via a host computer's serial port and plots a temperature control status diagram to monitor temperature changes over time. The heating process starts from ambient room temperature and gradually increases to the set target value. By adjusting the output power of the heating element, the temperature rise is ensured to be smooth and controllable. Calculations from the data in the diagram show that when the sensor is working normally, the temperature of the atomic gas chamber maintains a stable average value of 137.24℃ with a variance of 0.0011℃. 2 This indicates that the temperature fluctuation is very small.

[0145] The real-time temperature curve during the frequency stabilization control of the VCSEL laser is as follows: Figure 14 As shown in the figure, the data from the calculation shows that when the sensor is in a stable working state, the average temperature of the VCSEL laser is 72.85℃, and the temperature variance is... ℃ 2 This indicates that the temperature fluctuation of the VCSEL laser is very small.

[0146] In summary, this invention achieves multiple PID closed-loop control working in concert in an optically pumped magnetometer, transitions from open-loop to closed-loop control in alkali metal chamber temperature control, and utilizes multi-parameter coordinated PID control in VCSEL laser parameter control. Simultaneously, it precisely controls the temperature and laser current within the sensor, with a current accuracy error within 0.01%. Through precise monitoring and closed-loop control of the sensor's internal parameters, a variance of 0.0011℃ in the atomic chamber is achieved. 2 Temperature stability and VCSEL laser variance are ℃ 2 Temperature stability, with temperature control error within 5ppm.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A magnetic sensor control system, characterized by, The magnetic sensor, an atomic cell temperature control circuit, a laser temperature control circuit and a laser current control circuit are included; The atomic cell temperature control circuit is configured to heat an atomic cell of the magnetic sensor to a preset value, and then heat the atomic cell based on a negative feedback closed loop control algorithm to make the temperature of the atomic cell reach a set value, the preset value being less than the set value; an optical signal output by the atomic cell is converted into a voltage signal by a photodiode to determine an output voltage of the magnetic sensor; The laser temperature control circuit is configured to heat a laser of the magnetic sensor until an optical absorption characteristic curve of the atomic cell is obtained, and then cool the laser based on the optical absorption characteristic curve until the output voltage of the magnetic sensor reaches a preset frequency stabilization voltage value; The laser temperature control circuit is configured to heat a laser of the magnetic sensor until an optical absorption characteristic curve of the atomic cell is obtained, and then cool the laser based on the optical absorption characteristic curve until the output voltage of the magnetic sensor reaches a preset frequency stabilization voltage value; The laser current control circuit is configured to adjust a driving voltage of the laser based on a voltage negative feedback closed loop control algorithm to achieve closed loop control of a driving current of the laser after the output voltage of the magnetic sensor reaches the preset frequency stabilization voltage value.

2. The magnetic sensor control system of claim 1, wherein, The magnetic sensor control system includes a core controller; The atomic cell temperature control circuit includes an atomic cell temperature measurement circuit and an atomic cell heating circuit which are electrically connected to the core controller respectively; The laser temperature control circuit includes a laser temperature measurement circuit and a laser heating circuit which are electrically connected to the core controller respectively.

3. The magnetic sensor control system of claim 2, wherein, The working frequency of the heating driving signal of each of the atomic cell heating circuit and the laser heating circuit is different from the optimal working frequency of the magnetic sensor.

4. The magnetic sensor control system of claim 2 or 3, wherein, The atomic cell heating circuit and the laser heating circuit each include a gain amplification circuit, a heating filter circuit, a voltage and power amplification circuit and a heating sheet connected in sequence; The gain amplification circuit is configured to amplify an input heating driving signal to a gain multiple set by the core controller; The heating filter circuit is configured to filter out the direct current component of the amplified heating driving signal; The voltage and power amplification circuit is configured to perform voltage and power amplification on the filtered heating driving signal to drive the heating sheet.

5. The magnetic sensor control system of claim 2 or 3, wherein, The atomic cell temperature measurement circuit and the laser temperature measurement circuit each include a temperature detection element, a differential amplification circuit, a voltage amplification circuit and a temperature measurement filter circuit connected in sequence; The differential amplification circuit is configured to differentially amplify a voltage signal corresponding to the temperature detection element to obtain a differential voltage signal; The voltage amplification circuit is configured to amplify the differential voltage signal; and The temperature measurement filter circuit is configured to filter out the direct current component of the amplified differential voltage signal. The temperature measurement filter circuit is configured to filter high-frequency noise of the differential voltage signal after voltage amplification and output to the core controller, and the core controller is configured to determine the heating driving signal of the atomic gas chamber heating circuit and the laser heating circuit according to the received signal.

6. The magnetic sensor control system of claim 1, wherein, The laser current control circuit comprises a laser driving circuit, and the laser driving circuit comprises a differential amplifier, a reference resistor and a negative feedback circuit, and the output ends of the differential amplifier are connected with the reference resistor and the negative feedback circuit, respectively. The differential amplifier is configured to adjust the voltage difference across the reference resistor based on the negative feedback signal input by the negative feedback circuit so as to keep the current of the reference resistor constant.

7. A magnetic sensor control method characterized by, The magnetic sensor control system is implemented based on any one of claims 1-6, and the method comprises: After the atomic gas chamber of the magnetic sensor is heated to a preset value, the atomic gas chamber is heated based on a negative feedback closed-loop control algorithm so that the temperature of the atomic gas chamber is at a set value, and the preset value is less than the set value; The laser of the magnetic sensor is heated until the light absorption characteristic curve of the atomic gas chamber is obtained, and the laser is cooled based on the light absorption characteristic curve until the output voltage of the magnetic sensor reaches a preset frequency stabilization voltage value; After the output voltage of the magnetic sensor reaches the preset frequency stabilization voltage value, the driving voltage of the laser is adjusted based on a voltage negative feedback closed-loop control algorithm to realize closed-loop control of the driving current of the laser.

8. The magnetic sensor control method according to claim 7, wherein The heating of the atomic gas chamber based on the negative feedback closed-loop control algorithm so that the temperature of the atomic gas chamber is at a set value comprises: The atomic gas chamber is heated based on the negative feedback closed-loop control algorithm, and it is judged whether the temperature fluctuation range of the atomic gas chamber is within a first preset range; If the temperature fluctuation range of the atomic gas chamber is not within the first preset range, the parameters of the negative feedback closed-loop control algorithm are adjusted, the atomic gas chamber is heated based on the adjusted negative feedback closed-loop control algorithm, and the temperature fluctuation range of the atomic gas chamber is within a second preset range until the temperature fluctuation range of the atomic gas chamber is within the second preset range; The first preset range covers the second preset range.

9. The magnetic sensor control method according to claim 7 or 8, characterized by, Before the atomic gas chamber of the magnetic sensor is heated to a preset value, the method further comprises: The atomic gas chamber is heated in an open loop based on maximum power start, and the negative feedback closed-loop control algorithm is started.

Images