Magnetic measuring device

Abstract

To achieve stable magnetic field detection processing while improving the accuracy of magnetic field detection. [Solution] The magnetic sensor module 1 comprises a cell 4 containing an alkali metal, a pump laser light source 6 that emits pump light L into the cell 4, a photodiode 7 that detects the pump light L that has passed through the cell 4 and generates a magnetic field detection signal, a temperature sensor 13 that has a built-in resistance thermometer and outputs a detection signal that detects the temperature of the cell 4, and an amplifier 54 that amplifies the detection signal output from the temperature sensor 13.

Description

Technical Field

[0001] One aspect of the embodiment relates to a magnetic measurement device.

Background Art

[0002] Conventionally, there is known a magnetic sensor module including a cell filled with an alkali metal, a laser light source that emits laser light toward the inside of the cell, a light detection unit that detects the laser light that has passed through the cell, a magnetic field correction unit that corrects the magnetic field inside the cell, a correction process that controls the magnetic field correction unit to apply a correction magnetic field to the magnetic field inside the cell, and a detection process that detects a magnetic field based on an electrical signal from the light detection unit, and a control unit that executes the processes (see, for example, Non-Patent Document 1).

Prior Art Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] ​In the magnetic sensor module described above, it is necessary to increase the density of alkaline vapor in the cell, and the control unit must control the temperature inside the cell to a predetermined range. Therefore, a temperature sensor is required to measure the cell temperature. In a magnetic sensor module, however, in order to suppress the influence on measurement, it is preferable that the materials of the components constituting the magnetic sensor module are as non-magnetic as possible. For this reason, in conventional magnetic sensor modules, resistance temperature detectors (RTDs), which are temperature sensors that incorporate a resistor to measure the cell temperature, have been frequently used for the above control. However, it has been found that in such temperature sensors, a magnetic field is generated by the current supplied when the temperature sensor is driven, which can affect the detection of the magnetic field. In particular, when performing temperature measurement with higher precision in order to perform stable magnetic field detection processing, it is necessary to increase the amount of current used during driving, so the influence of the magnetic field generated by the temperature sensor becomes greater, and the accuracy of magnetic field detection can decrease.

[0005] Therefore, one aspect of the embodiment was made in view of the above problems, and aims to provide a magnetic measuring device that achieves stable magnetic field detection processing while improving the accuracy of magnetic field detection. [Means for solving the problem]

[0006] A magnetic measuring device according to a first aspect of the embodiment comprises a cell containing an alkali metal, a laser light source that emits laser light into the cell, a photodetector that detects the laser light that has passed through the cell and generates a magnetic field detection signal, a temperature sensor that has a built-in resistor and outputs a detection signal that detects the temperature of the cell, and an amplification unit that amplifies the detection signal output from the temperature sensor.

[0007] Alternatively, a magnetic detection device according to a second aspect of the embodiment comprises a cell containing an alkali metal, a laser light source that emits laser light into the cell, a photodetection unit that detects the laser light that has passed through the cell and generates a photodetection signal, a coil that applies a magnetic field in a predetermined direction within the cell, a temperature sensor that has a built-in resistor and outputs a detection signal that detects the temperature of the cell, and a control unit that supplies a modulated signal having a modulation frequency to the coil, measures the magnetic field strength within the cell based on a magnetic field detection signal generated based on the photodetection signal output from the photodetection unit, and drives the resistor of the temperature sensor at a drive frequency higher than the modulation frequency.

[0008] According to the magnetic detection device relating to the first aspect described above, the cell temperature is detected by a temperature sensor and a detection signal is output, and the detection signal from the temperature sensor is amplified by an amplification unit. With this configuration, the signal amount of the detection signal itself can be kept smaller, and therefore the amount of current required to drive the temperature sensor can be kept smaller. As a result, it is possible to reduce magnetic noise generated from the temperature sensor while performing highly accurate temperature measurement. Thus, stable magnetic field detection processing is possible while improving the detection accuracy of the magnetic field in the cell.

[0009] On the other hand, according to the magnetic detection device relating to the second aspect described above, a temperature sensor driven by the control unit at a driving frequency outputs a detection signal having the driving frequency. The control unit also supplies a modulation signal having a modulation frequency to a coil that applies a magnetic field in a predetermined direction within the cell. Here, the driving frequency is higher than the modulation frequency of the modulation signal. With this configuration, it becomes easy to remove low-frequency components of magnetic noise caused by the current used to drive the temperature sensor while performing highly accurate temperature measurement without suppressing the driving current of the temperature sensor. Therefore, stable magnetic field detection processing is possible while improving the detection accuracy of the magnetic field within the cell.

[0010] In the first or second aspect described above, the resistor is preferably a platinum resistor. In this case, the temperature sensor can be made of a non-magnetic material, and the detection accuracy of the magnetic field in the cell can be further improved.

[0011] Furthermore, in the first or second aspect described above, it is also preferable that the temperature sensor outputs the voltage across a resistor when a constant current is supplied as a detection signal. In this case, the temperature of the cell can be evaluated by the voltage value indicated by the detection signal output by the temperature sensor, and stable magnetic field detection processing can be performed using the evaluation result.

[0012] Furthermore, in the first or second aspect described above, it is also preferable that the temperature sensor outputs the terminal voltage of a resistor as a detection signal when a divided voltage, which is a constant voltage, is supplied to it. In this case, the temperature of the cell can be evaluated by the voltage value indicated by the detection signal output by the temperature sensor, and stable magnetic field detection processing can be performed using the evaluation result.

[0013] Furthermore, in the first aspect described above, it is preferable that the amplification unit includes an amplifier connected to the terminals of the resistor and which amplifies the detection signal. In this case, the detection signal can be amplified and output by the amplifier. As a result, the supply current for driving the temperature sensor can be reduced, thereby reducing magnetic noise generated from the temperature sensor and improving the detection accuracy of the magnetic field in the cell.

[0014] Furthermore, in the second aspect described above, it is also preferable that the control unit includes a drive source that supplies a voltage divider voltage having a driving frequency or a constant current to the resistor. In this case, the temperature of the cell can be evaluated by the voltage value indicated by the detection signal output by the temperature sensor driven by the drive source, and stable magnetic field detection processing can be performed using the evaluation result.

[0015] The magnetic detection device of the embodiment includes [1] a cell containing an alkali metal, A laser light source that emits laser light into the cell, A photodetector that detects the laser light that has passed through the cell and generates a magnetic field detection signal, A temperature sensor that incorporates a resistor and outputs a detection signal that detects the temperature of the cell, An amplification unit that amplifies the detection signal output from the temperature sensor, It is a magnetic measuring device equipped with [a specific feature].

[0016] The magnetic detection device of the embodiment includes [2] a cell containing an alkali metal, A laser light source that emits laser light into the cell, A photodetection unit that detects the laser light that has passed through the cell and generates a photodetection signal, A coil that applies a magnetic field in a predetermined direction within the cell, A temperature sensor that incorporates a resistor and outputs a detection signal that detects the temperature of the cell, A control unit having the function of supplying a modulated signal having a modulation frequency to the coil, measuring the magnetic field strength in the cell based on a magnetic field detection signal generated based on the photodetection signal output from the photodetection unit, and driving the resistor of the temperature sensor at a drive frequency higher than the modulation frequency, It is a magnetic measuring device equipped with [a specific feature].

[0017] The magnetic detection device of the embodiment [3] "The resistor is a platinum resistor, The magnetic measuring device described in [1] or [2] above may also be the same.

[0018] The magnetic detection device of the embodiment [4] "The temperature sensor outputs the voltage across the resistor when a constant current is supplied as the detection signal, The magnetic measuring device described in [1] to [3] above may also be used.

[0019] The magnetic detection device of the embodiment [5] "The temperature sensor outputs the terminal voltage of the resistor when a divided voltage obtained by dividing a constant voltage is supplied as the detection signal, The magnetic measuring device described in [1] to [3] above may also be used.

[0020] The magnetic detection device of the embodiment [6] "The amplification unit includes an amplifier connected to the terminals of the resistor and which amplifies the detection signal, It may be the "magnetic measurement device" described in [1] above.

[0021] The magnetic detection device of the embodiment includes, in [7], "the control unit includes a drive source that supplies a voltage-divided voltage or a constant current having the drive frequency to the resistor." It may be the "magnetic measurement device" described in [2] above.

Advantages of the Invention

[0022] According to one aspect of the embodiment, stable magnetic field detection processing can be realized while enhancing the detection accuracy of the magnetic field.

Brief Description of the Drawings

[0023] [ [Figure 1] FIG. 1 is a block diagram showing a magnetic detection system including a magnetic measurement device according to the first embodiment. [Figure 2] FIG. 2 is a schematic configuration diagram showing the magnetic sensor module of FIG. 1. [Figure 3] FIG. 3 is a diagram showing in detail the configuration of the cell temperature control unit 31 of the control circuit 3 in FIG. 2. [Figure 4] FIG. 4 is a flowchart showing the flow of detection processing by the magnetic detection system 100 in FIG. 1. [Figure 5] FIG. 5 is a graph showing the frequency characteristics of the optical detection signal detected when a 100 Hz modulation signal is applied into the cell 4. [Figure 6] FIG. 6 is a diagram showing in detail the configuration of the cell temperature control unit 31 in the control circuit 3A according to the second embodiment.

Modes for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals will be used for the same elements or elements having the same function, and redundant descriptions will be omitted.

[0025] [First Embodiment]

[0026] Figure 1 is a block diagram showing a magnetic detection system equipped with a magnetic measuring device according to the first embodiment. Figure 2 is a schematic configuration diagram showing a magnetic sensor module, which is a magnetic measuring device according to the first embodiment. The magnetic sensor module is a device that measures magnetic fields using optical pumping. The magnetic sensor module 1 is used for the purpose of biomedical measurement such as magnetoencephalography and magnetospinal spectroscopy, or for the purpose of material analysis such as NMR (Nuclear Magnetic Resonance), but its use is not limited to these. In Figure 2, the X-axis is taken in the direction along the incident direction of pump light to the cell, which will be described later, the X-axis is taken perpendicular to the Y-axis, and the Z-axis is taken perpendicular to the Y-axis and X-axis. Also in Figure 2, the propagation path of light is shown by a dotted line, and the transmission paths of power and signal are shown by solid lines with arrows.

[0027] As shown in Figure 1, the magnetic detection system 100 comprises a magnetic sensor module 1 and a control device 10. The magnetic sensor module 1 comprises a magnetic sensor 2 and a control circuit 3 (control unit). The control device 10 controls the operation of the magnetic sensor 2 by controlling the control circuit 3. The control device 10 is a PC or an MCU (Microcontroller Unit), etc. The control circuit 3 is a drive board that drives the magnetic sensor 2 and incorporates, for example, an MCU and an FPGA (Field Programmable Gate Array) or other arithmetic circuits. Note that the control circuit 3 may be integrated with the control device 10, in which case the magnetic detection system 100 can be considered as the magnetic sensor module 1.

[0028] As shown in Figure 2, the magnetic sensor 2 comprises a cell 4, a heater 5, a pump laser light source (laser light source) 6, a photodiode (light detection unit) 7, a magnetic field correction unit 8, a current source 9, an amplifier 11, a heater control circuit 12, and a temperature sensor 13. The details of each component of the magnetic sensor module 1 will be described below.

[0029] Cell 4 has a shape that is, for example, a roughly rectangular parallelepiped and bottomed cylindrical shape, and is made of a material that is light-transmitting to the pump light L described later. The material of cell 4 is, for example, quartz, sapphire, silicon, Kovar glass, borosilicate glass, etc. Cell 4 contains alkali metals and a sealed gas. The alkali metal sealed in cell 4 may be, for example, at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). The sealed gas protects alkali metal vapors and suppresses noise emission. The sealed gas may be an inert gas such as helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N2), etc.

[0030] The heater 5 is located close to the cell 4 and heats the inside of the cell 4. The heater 5 generates heat in accordance with the current supplied from the heater control circuit 12, which will be described later. Based on the detection signal from the temperature sensor 13, which measures the internal temperature of the cell 4, the heater 5 controls the supply current of the heater control circuit 12 so that the internal temperature of the cell 4 reaches a predetermined temperature (for example, 180°C), thereby vaporizing alkali metals inside the cell 4 and controlling the vapor density.

[0031] The pump laser light source 6 emits pump light L (laser light) towards the cell 4 along the X-axis direction (first direction). The pump laser light source 6 emits pump light L in a circularly polarized state to excite alkali metal atoms. The pump laser light source 6 may shape the pump light L to any size. The alkali metal atoms contained in the cell 4 are excited by the pump light L. The wavelength of the pump light L is set according to the type of atoms constituting the alkali metal vapor (more specifically, the wavelength of the absorption line), and is set to match, for example, the absorption wavelength of alkali. In the first embodiment, the driving conditions of the pump laser light source 6 are determined by the control circuit 3, and the intensity and wavelength of the pump light L emitted from the pump laser light source 6 can be adjusted by control by the control circuit 3. To realize such control, the pump laser light source 6 has a wavelength control function, such as a function that allows the oscillation wavelength to be controlled using an external resonator, or a configuration that allows the oscillation wavelength to be controlled by temperature control of the laser element.

[0032] The photodiode 7 is a detection unit that detects the pump light L that has passed through the cell 4 outside of the cell 4. The pump light L that has passed through the inside of the cell 4 is incident on the photodiode 7. The photodiode 7 generates and outputs an electrical signal corresponding to the frequency distribution of the intensity of the pump light L. The amplifier 11 amplifies the electrical signal output from the photodiode 7 and generates a photodetection signal (magnetic field detection signal) that detects the intensity of the pump light L that has passed through the cell 4. The amplifier 11 outputs the amplified photodetection signal to the control circuit 3.

[0033] The magnetic field correction unit 8 corrects the magnetic field within the cell 4. Specifically, the magnetic field correction unit 8 is a group of coils provided around the cell 4 to correct and cancel noise components in the X, Y, and Z axes when detecting the environmental magnetic field, such as the Earth's magnetic field, in the space where the cell 4 exists, i.e., the magnetic field of the object being measured. The magnetic field correction unit 8 includes, for example, a first correction coil 8a, a second correction coil 8b, and a third correction coil 8c, which are wound around the X, Y, and Z axes, respectively. The first correction coil 8a, the second correction coil 8b, and the third correction coil 8c each generate a first correction magnetic field along the X axis, a second correction magnetic field along the Y axis, and a third correction magnetic field along the Z axis, respectively, using current supplied from the current source 9, and apply them to the cell 4. Specifically, the first correction coil 8a corrects the strength of the magnetic field in the X-axis direction included in the magnetic field within cell 4, the second correction coil 8b corrects the strength of the magnetic field in the Y-axis direction included in the magnetic field within cell 4, and the third correction coil 8c corrects the strength of the magnetic field in the Z-axis direction included in the magnetic field within cell 4. The magnetic field correction unit 8 operates to cancel the ambient magnetic field in the space in which cell 4 exists by controlling the supply current of the current source 9 to the first correction coil 8a, the second correction coil 8b, and the third correction coil 8c by the control circuit 3.

[0034] The temperature sensor 13 is located close to the cell 4, detects the cell temperature (external temperature of the cell), outputs a detection signal, and incorporates a resistance thermometer (RTD) made of platinum or copper. From the viewpoint of detection accuracy, detection stability, and detectable temperature range, the resistance thermometer incorporated in the temperature sensor 13 is preferably a platinum resistor. Specifically, the temperature sensor 13 outputs the voltage across its terminals as a detection signal when a constant voltage is supplied from the control circuit 3 through a voltage divider (details will be described later).

[0035] The control circuit 3 performs a detection process to acquire the magnetic field strength based on the photodetection signal from the photodiode 7. Specifically, the control circuit 3 derives the magnetic field strength within cell 4 based on the amplified photodetection signal from amplifier 11. For example, the control circuit 3 detects the change in transmittance of the pump light L, which is circularly polarized light that has passed through cell 4, caused by the change in the magnetic field within cell 4, and derives the magnetic field strengths in the Y-axis direction and the Z-axis direction within cell 4 based on the change in transmittance. The control circuit 3 outputs the derived results to the control device 10.

[0036] Furthermore, the control circuit 3 determines the operating conditions (driving conditions) of the pump laser light source 6. Specifically, the control circuit 3 controls the wavelength of the pump light L emitted by the pump laser light source 6. For example, the control circuit 3 adjusts the wavelength of the pump light L to the absorption wavelength of the alkali metal sealed in the cell 4.

[0037] As shown in Figure 1, the control circuit 3 comprises a cell temperature control unit 31, a laser temperature control unit 32, a magnetic field control unit 33, and a signal processing unit 34. The functions of each functional part of the control circuit 3 will be described in detail below.

[0038] The cell temperature control unit 31 adjusts the internal temperature of cell 4. Specifically, it receives an instruction (start trigger) from the control device 10 to adjust the internal temperature of cell 4 and starts control to adjust the internal temperature of cell 4. Based on the detection signal (RTD resistance value) from the temperature sensor 13 that measures the external temperature of cell 4, the cell temperature control unit 31 controls the current supplied by the heater control circuit 12 to the heater 5, for example, by PID (Proportional Integral Differential) control, so that the internal temperature of cell 4 reaches a predetermined temperature (for example, 180°C).

[0039] The laser temperature control unit 32 adjusts the temperature of the pump laser light source 6 (specifically, the temperature of the laser element built into the pump laser light source 6). Specifically, the laser temperature control unit 32 receives an instruction (start trigger) from the control device 10 to adjust the temperature of the pump laser light source 6 and starts the process of controlling the temperature. The control circuit 3 adjusts the temperature of the pump laser light source 6 to a predetermined temperature, for example by PID control, based on a detection signal (RTD resistance value) from a temperature sensor (not shown) that measures the temperature of the pump laser light source 6 and a photodetection signal output from the photodiode 7. This predetermined temperature is the temperature at which the wavelength of the pump light L matches the absorption wavelength of the alkali metal sealed in the cell 4. In detail, the laser temperature control unit 32 monitors the photodetection signal while sweeping the temperature of the pump laser light source 6, searches for the temperature at which the absorption of the alkali metal in the cell 4 is maximum, that is, the temperature at which the output of the photodiode 7 is minimum, and sets that temperature as the target value. The laser temperature control unit 32 then performs PID control so that the temperature calculated from the RTD resistance value (the temperature of the pump laser light source 6) reaches the target value.

[0040] The magnetic field control unit 33 performs a correction process to correct the magnetic field within cell 4. Specifically, the magnetic field control unit 33 receives an instruction (start trigger) from the control device 10 to perform the correction process and starts the correction process. Based on the photodetection signal output from the photodiode 7, the magnetic field control unit 33 controls the supply current to the first correction coil 8a, the second correction coil 8b, and the third correction coil 8c of the current source 9 to generate a first correction magnetic field along the X-axis, a second correction magnetic field along the Y-axis, and a third correction magnetic field along the Z-axis, respectively. That is, the magnetic field control unit 33 sweeps the first correction magnetic field and adjusts its magnetic field so that the absorption of alkali metals within cell 4 is maximized. The magnetic field control unit 33 also sweeps the second correction magnetic field and adjusts its magnetic field so that the absorption of alkali metals within cell 4 is minimized, and sweeps the third correction magnetic field and adjusts its magnetic field so that the absorption of alkali metals within cell 4 is minimized.

[0041] Furthermore, when the detection process for acquiring the strength of the magnetic field in cell 4 is performed, the magnetic field control unit 33 controls the supply current to the second correction coil, which includes a first modulation signal having the first modulation frequency, in order to superimpose a signal having the first modulation frequency onto the second correction magnetic field along the Y-axis. Furthermore, when the detection process for acquiring the strength of the magnetic field in cell 4 is performed, the magnetic field control unit 33 controls the supply current to the third correction coil, which includes a second modulation signal having the second modulation frequency, in order to superimpose a signal having the second modulation frequency different from the first modulation frequency onto the third correction magnetic field along the Z-axis.

[0042] The signal processing unit 34 performs a detection process to acquire the strength of the magnetic field within cell 4. Specifically, the signal processing unit 34 receives an instruction (start trigger) from the control device 10 to perform the detection process and starts the detection process. Based on the photodetection signal output from the photodiode 7, the signal processing unit 34 derives the strength of the magnetic field within cell 4 and outputs the derived result to an external device such as the control device 10. In the first embodiment, the signal processing unit 34 derives the strength of the Y-axis magnetic field by demodulating the photodetection signal using a first modulation signal of a first modulation frequency, and derives the strength of the Z-axis magnetic field by demodulating the photodetection signal using a second modulation signal of a second modulation frequency. The signal processing unit 34 then formats the derived magnetic field strength into an appropriate signal format and outputs it externally via an external output connector.

[0043] Referring to Figure 3, the configuration of the cell temperature control unit 31 of the control circuit 3 will be described in detail. Figure 3 shows only the configuration of the cell temperature control unit 31 in the control circuit 3. The cell temperature control unit 31 includes, for example, a reference voltage source (drive source) 51 that supplies a constant voltage of 1V, a fixed resistor element 52, a capacitor 53, an amplifier (amplifier) ​​54, resistor elements 55, 56, an A / D converter (ADC) 57, a feedback control unit 58, a D / A converter (DAC) 59, and an amplifier 60. The cell temperature control unit 31 is configured to send and receive various signals with the magnetic sensor 2 via a cable 62 connected to a connector 61 provided in the control circuit 3.

[0044] The fixed resistor element 52 has a constant resistance value (e.g., 10kΩ), one end of which is connected to the output of the reference voltage source 51, and the other end of which is connected to one end of the resistance thermometer of the temperature sensor 13 in the magnetic sensor 2 via the connector 61 and cable 62. The other end of the resistance thermometer of the temperature sensor 13 in the magnetic sensor 2 is connected to a reference potential (e.g., ground potential) in the control circuit 3 via the cable 62 and connector 61. With this configuration, the constant voltage output from the reference voltage source 51 is supplied to the resistance thermometer of the temperature sensor 13 after being split between it and the fixed resistor element 52. The capacitor 53 has one end of which is connected to the other end of the fixed resistor element 52 and one end of the resistance thermometer of the temperature sensor 13, and the other end of which is connected to the reference potential. The fixed resistor element 52 and the capacitor 53 function as a low-pass filter, cutting out high-frequency components from the voltage applied from the reference voltage source 51 and supplying it to the resistance thermometer of the temperature sensor 13. The order of connection between the fixed resistor element 52 and the capacitor 53 may be reversed.

[0045] Amplifier 54 has its first input connected to the other end of a fixed resistor element 52 and one end of a capacitor 53, and its second input connected to two resistor elements 55 and 56. It amplifies the voltage of the first input, with reference to a reference potential, by a predetermined amplification factor and outputs the amplified voltage from its output. In this embodiment, amplifier 54 outputs the voltage across the resistance thermometer, with reference to a reference potential, as a detection signal output from the temperature sensor 13, by a predetermined amplification factor. Specifically, resistor element 55 is connected between the reference potential and the second input of amplifier 54, and resistor element 56 is connected between the second input of amplifier 54 and the output of amplifier 54. At this time, the amplification factor of amplifier 54 is determined by the resistance ratio of resistor element 55 and resistor element 56. For example, if the resistance value of resistor element 55 is 1 kΩ and the resistance value of resistor element 56 is 10 kΩ, the amplification factor is set to 10 times.

[0046] The ADC 57 has its input connected to the output of the amplifier 54 and performs A / D conversion on the detection signal output from the amplifier 54. The ADC 57 outputs the A / D converted detection signal to the feedback control unit 58. Alternatively, the ADC 57 may monitor the output voltage of the reference voltage source 51, perform A / D conversion on that output voltage, and output it to the feedback control unit 58.

[0047] The feedback control unit 58 is implemented within the arithmetic circuit such as an MCU or FPGA in the control circuit 3. As described above, the feedback control unit 58 generates an instruction signal, for example by PID control, to adjust the supply current of the heater 5 to the heater control circuit 12 so that the internal temperature of the cell 4 reaches a predetermined temperature, based on the detection signal (RTD resistance value) from the temperature sensor 13. When performing PID control, the feedback control unit 58 derives the RTD resistance value from the value of the detection signal and the output voltage value of the reference voltage source 51.

[0048] The DAC59 has its input connected to the output of the feedback control unit 58 and performs D / A conversion on the instruction signal output from the feedback control unit 58. The output of the DAC59 is connected to one control input of the heater control circuit 12 of the magnetic sensor 2 via an amplifier 60, which is a voltage follower, a connector 61, and a cable 62. The other control input of the heater control circuit 12 is connected to a reference potential in the control circuit 3 via the cable 62 and connector 61. With this configuration, the instruction signal generated by the feedback control unit 58 is input to the heater control circuit 12, and the internal temperature of the cell 4 in the magnetic sensor 2 is adjusted. Here, the amplifier 60 constitutes a voltage follower, but it may also be configured to amplify the output of the DAC59.

[0049] Next, with reference to Figure 4, the operation procedure of the detection process by the magnetic detection system 100 will be explained. Figure 4 is a flowchart showing the flow of the detection process by the magnetic detection system 100.

[0050] First, a start trigger is generated by a switch or the like provided in the control device 10 or the control circuit 3. When the control circuit 3 receives the start trigger, the internal temperature of the cell 4 is adjusted by the cell temperature control unit 31 (step S01). Specifically, the cell temperature control unit 31 controls the current supplied to the heater 5 based on the detection signal from the temperature sensor 13 so that the internal temperature of the cell 4 reaches a predetermined temperature.

[0051] Next, when the internal temperature of cell 4 reaches a predetermined temperature, an instruction (start trigger) to adjust the emission wavelength of the pump laser light source 6 is sent from the control device 10 to the control circuit 3, and the process of adjusting the emission wavelength of the pump laser light source 6 is started (step S02). Specifically, the laser temperature control unit 32 controls the temperature of the pump laser light source 6 so that it reaches the temperature at which absorption by alkali metals in cell 4 is maximized.

[0052] Subsequently, when the temperature of the pump laser light source 6 reaches the target temperature, an instruction (start trigger) to start the correction process to correct the magnetic field in cell 4 is sent from the control device 10 to the control circuit 3, and the correction process is started (step S03). In detail, the magnetic field control unit 33 adjusts the supply current to the magnetic field correction unit 8 to generate a first correction magnetic field, a second correction magnetic field, and a third correction magnetic field based on the photodetection signal output from the photodiode 7.

[0053] Next, once the settings for the first, second, and third correction magnetic fields are complete, an instruction (start trigger) to begin the detection process for acquiring the magnetic field strength within cell 4 is sent from the control device 10 to the control circuit 3, and the detection process begins (step S04). Specifically, the signal processing unit 34 detects the strength of the Y-axis magnetic field and the Z-axis magnetic field by demodulating the photodetection signal output from the photodiode 7. Finally, the signal processing unit 34 formats the detection result of the magnetic field strength into an appropriate signal and outputs it externally (step S05).

[0054] According to the magnetic detection system 100 described above, the temperature of cell 4 is detected by the temperature sensor 13, a detection signal is output, and the detection signal of the temperature sensor 13 is amplified. With this configuration, the signal amount of the detection signal itself can be kept smaller, and therefore the amount of current required to drive the temperature sensor 13 can be kept smaller. As a result, it is possible to reduce magnetic noise generated from the temperature sensor 13 while performing highly accurate temperature measurement. Thus, stable magnetic field detection processing is possible while improving the detection accuracy of the magnetic field in cell 4.

[0055] In this embodiment, the resistance thermometer built into the temperature sensor 13 is a platinum resistance thermometer. In this case, the temperature sensor 13 can be made of a non-magnetic material, and the detection accuracy of the magnetic field in the cell 4 can be further improved.

[0056] Furthermore, in this embodiment, the temperature sensor 13 is configured to output the terminal voltage of the resistance thermometer as a detection signal when a divided voltage, which is a constant voltage, is supplied to it. In this case, the temperature inside the cell 4 can be evaluated by the voltage value indicated by the detection signal output by the temperature sensor 13, and stable magnetic field detection processing can be performed using the evaluation result.

[0057] Furthermore, in this embodiment, the control circuit 3 includes an amplifier 54 connected to the terminals of the temperature sensor 13's resistance thermometer, which amplifies the detection signal. In this case, the detection signal can be amplified and output by the amplifier 54. As a result, the supply current for driving the temperature sensor 13 can be reduced, thereby reducing magnetic noise generated from the temperature sensor 13 and improving the detection accuracy of the magnetic field in the cell 4.

[0058] The effects of this embodiment will be explained with reference to Figure 5. Figure 5 is a graph showing the frequency characteristics of the photodetection signal detected when a 100 Hz modulated signal is applied to cell 4. Here, the frequency characteristics of this embodiment and the frequency characteristics of a comparative example in which the amplifier 54 and resistor elements 55 and 56 are removed from the configuration of this embodiment are shown. In this embodiment, it was found that the supply current of the resistance thermometer can be reduced to 1 / 10 compared to the comparative example, and as a result, the noise superimposed on the photodetection signal can be reduced. [Second Embodiment]

[0059] Next, the configuration of the control circuit 3A according to the second embodiment will be described. Figure 6 is a diagram showing in detail the configuration of the cell temperature control unit 31 in the control circuit 3A according to the second embodiment.

[0060] Compared to the first embodiment, the cell temperature control unit 31 of the control circuit 3A differs in that it includes a reference AC source (drive source) 51A instead of a reference voltage source 51, a capacitor 53A is added between the reference AC source 51A and the fixed resistor element 52, and the input of the ADC 57 is directly connected to the other end of the fixed resistor element 52 without going through the amplifier 54.

[0061] The reference AC source 51A is a current source that supplies an alternating current with a constant amplitude (constant current) having a predetermined drive frequency (e.g., 5 kHz) that is higher than the first and second modulation frequencies. For example, the reference AC source 51A is a current source that generates an alternating current with a drive frequency of 5 kHz and an amplitude of 1 Vp-p, and is configured by a combination of FPGA and DAC, or by a DDS (Direct Digital Synthesizer). The capacitor 53A is connected between the reference AC source 51A and the fixed resistor element 52, and together with the fixed resistor element 52, forms a high-pass filter, cutting out the DC component, which is a low-frequency component, from the alternating current output from the reference AC source 51A. With this configuration, the alternating current generated from the reference AC source 51A is supplied to the resistance thermometer of the temperature sensor 13 via the fixed resistor element 52, and the resistance thermometer is driven.

[0062] The ADC57 performs A / D conversion on the effective value of the voltage across the temperature sensor 13's resistance thermometer, when a constant amplitude AC current is supplied to it, and uses it as a detection signal. The ADC57 outputs the A / D converted detection signal to the feedback control unit 58.

[0063] The feedback control unit 58 generates an instruction signal to adjust the supply current of the heater 5 by PID control, in the same manner as in the first embodiment. At this time, the feedback control unit 58 derives the RTD resistance value based on the value of the detection signal and the effective value of the AC current generated by the reference AC source 51A.

[0064] In the second embodiment described above, the temperature sensor 13 is driven by an alternating current with a drive frequency higher than the modulation frequency of the modulation signal superimposed on the magnetic field in cell 4. With this configuration, high-precision temperature control can be performed without suppressing the drive current of the temperature sensor 13, while easily removing the low-frequency component of the magnetic noise caused by the alternating current used to drive the temperature sensor 13. Therefore, stable magnetic field detection processing is possible while improving the detection accuracy of the magnetic field in cell 4.

[0065] In the second embodiment, the temperature sensor 13 outputs the effective value of the voltage across the resistance thermometer when a constant amplitude AC current is supplied as a detection signal. In this case, the temperature inside the cell 4 can be evaluated by the voltage value indicated by the detection signal output by the temperature sensor 13, and stable magnetic field detection processing can be performed using the evaluation result.

[0066] Furthermore, in the second embodiment, a reference AC power source 51A is provided that supplies an AC current with a constant amplitude having a driving frequency to the temperature sensor 13's resistance thermometer. In this case, the temperature inside the cell 4 can be evaluated by the voltage value indicated by the detection signal output by the temperature sensor 13 driven by the reference AC power source 51A, and stable magnetic field detection processing is possible using the evaluation result.

[0067] Although various embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and may be modified or applied to other things without changing the gist of each claim.

[0068] The control circuit 3 according to the first embodiment described above may include a current source that supplies a constant current instead of a reference voltage source 51 that supplies a constant voltage. In that case, the feedback control unit 58 derives the RTD resistance value based on the value of the detection signal and the current value generated by the current source.

[0069] Furthermore, the control circuit 3A according to the second embodiment may include a voltage source that supplies an AC voltage of a constant amplitude (constant voltage) instead of the reference AC source 51A. In that case, the feedback control unit 58 derives the RTD resistance value based on the value of the detection signal and the effective value of the AC voltage generated by the voltage source. [Explanation of symbols]

[0070] 1...Magnetic sensor module (magnetic measuring device), 3...Control circuit (control unit), 4...Cell, 5...Heater, 6...Pump laser light source (laser light source), 7...Photodiode (light detection unit), 8...Magnetic field correction unit, 8a...First correction coil, 8b...Second correction coil, 8c...Third correction coil, 13...Temperature sensor, 54...Amplifier (amplification unit), 51...Reference voltage source (drive source), 51A...Reference AC source (drive source), L...Pump light (laser light), 100...Magnetic detection system.

Claims

1. Cells containing alkali metals, A laser light source that emits laser light into the cell, A photodetector that detects the laser light that has passed through the cell and generates a magnetic field detection signal, A temperature sensor that incorporates a resistor and outputs a detection signal that detects the temperature of the cell, An amplification unit that amplifies the detection signal output from the temperature sensor, A magnetic measuring device equipped with the following features.

2. Cells containing alkali metals, A laser light source that emits laser light into the cell, A photodetection unit that detects the laser light that has passed through the cell and generates a photodetection signal, A coil that applies a magnetic field in a predetermined direction within the cell, A temperature sensor that incorporates a resistor and outputs a detection signal that detects the temperature of the cell, A control unit having the function of supplying a modulated signal having a modulation frequency to the coil, measuring the magnetic field strength in the cell based on a magnetic field detection signal generated based on the photodetection signal output from the photodetection unit, and driving the resistor of the temperature sensor at a drive frequency higher than the modulation frequency, A magnetic measuring device equipped with the following features.

3. The resistor is a platinum resistor. The magnetic measuring device according to claim 1 or 2.

4. The temperature sensor outputs the voltage across the resistor when a constant current is supplied as the detection signal. The magnetic measuring device according to claim 1 or 2.

5. The temperature sensor outputs the terminal voltage of the resistor as the detection signal when a divided voltage, which is a constant voltage, is supplied to it. The magnetic measuring device according to claim 1 or 2.

6. The amplification unit includes an amplifier connected to the terminals of the resistor and which amplifies the detection signal. The magnetic measuring device according to claim 1.

7. The control unit includes a drive source that supplies a voltage divider voltage having the drive frequency or a constant current to the resistor. The magnetic measuring device according to claim 2.

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