A mu-kelvin level temperature measurement system based on two-stage induction voltage division and a design method thereof

Abstract

The application provides a muK-level temperature measurement system and a design method based on two-stage induction voltage division, and the method comprises the following steps: constructing an alternating current temperature measurement bridge based on two-stage induction voltage division, taking the alternating current temperature measurement bridge as a measurement structure, using an alternating current excitation source to suppress 1 / f noise and power frequency interference through frequency modulation and frequency domain filtering; designing a two-stage induction voltage divider; selecting an NTC thermistor as a temperature measurement sensor; integrating an analog switch, a differential operational amplifier and a microcontroller; analyzing noise sources of a circuit, selecting elements based on a noise power spectrum, combining consistency testing and metrological calibration, and forming a path for improving performance of the sensor. The method is based on the key technology of the high-resolution alternating current temperature measurement bridge based on two-stage induction voltage division, and the high-precision temperature measurement system with a wide temperature range and a muK-level measurement range is realized by designing an analog switch, a differential operational amplifier and a microcontroller to control the program-controlled voltage division.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of temperature measurement, and particularly provides a muK-level temperature measurement system based on secondary induction voltage division and a design method. BACKGROUND

[0002] In the aspects of gravitational wave detection, semiconductor chip manufacturing and rock thermal stress observation related to earthquake prediction, the temperature measurement system needs to have muK-level temperature measurement resolution. In the aspect of gravitational wave detection, the temperature measurement needs to have several muK-level resolutions in the range of 1mHz-0.1Hz. In the aspect of earthquake prediction, the weak temperature change caused by the stress of rock before and after instability can be used to identify the sub-instability stage and then judge the possibility of earthquake occurrence. Since the thermal stress coefficient of rock is small, for example, the thermal stress coefficient of diorite granite is only 0.7mK / Mpa, the stress change is reflected through temperature measurement, and very high measurement resolution is needed.

[0003] The existing temperature measurement system has obvious limitations and cannot meet the above requirements: the direct current bridge temperature measurement system: when measuring temperature change, the resistance change caused by temperature belongs to low-frequency slow-changing signal, which overlaps with the main frequency band of the widely existing 1 / f noise, and cannot effectively suppress the influence of 1 / f noise and power frequency interference and other low-frequency error sources, which will limit the measurement accuracy and make it difficult to meet the muK-level temperature measurement resolution requirement. The traditional resistance voltage division temperature measurement system: the resistance voltage division method has the problem of resistance aging, and the accuracy of the voltage division ratio is limited, and the error can be higher than 10 -9 , which will reduce the voltage control accuracy of the comparison point, affect the overall performance and measurement accuracy of the temperature measurement system, and is not conducive to realizing high-precision temperature measurement.

[0004] Therefore, there is an urgent need for a design method of a muK-level temperature measurement system based on secondary induction voltage division to solve the above problems. SUMMARY

[0005] In order to overcome the above defects, the application is provided to solve or partially solve the above problems.

[0006] In one aspect, the application provides a design method of a μK-level temperature measurement system based on two-stage induction voltage division, comprising the following steps: constructing an AC temperature measurement bridge based on two-stage induction voltage division, using the AC temperature measurement bridge as a measurement structure, using an AC excitation source to suppress 1 / f noise and power frequency interference through frequency modulation and frequency domain filtering; designing a two-stage induction voltage divider, the two-stage voltage divider comprising: a primary induction voltage divider configured to provide an excitation voltage to the bridge, including independently set excitation windings; a secondary induction voltage divider provided with multiple taps, a variable turns ratio being formed by selecting the taps; one winding tap of the primary induction voltage divider being strongly coupled with the secondary induction voltage divider; selecting an NTC thermistor as a temperature measurement sensor; integrating an analog switch, a differential operational amplifier, and a microcontroller, wherein the analog switch is used to switch different voltage division circuits, the differential operational amplifier amplifies the weak differential signal output by the bridge, and the microcontroller is used to program the first switch and the second switch according to the ratio of the real-time measured thermistor and the reference standard resistor, to realize bridge balance adjustment, and simultaneously process measurement data to complete temperature calculation and output; analyzing the noise sources of the circuit, selecting components based on the noise power spectrum, and combining consistency testing and metrological calibration to form a path for improving sensor performance.

[0007] In one technical solution of the above-mentioned design method of a μK-level temperature measurement system based on two-stage induction voltage division, the relationship between the resistance value of the temperature measurement sensor and the temperature change is: In the formula, β represents the temperature characteristic of the material, R0 represents the resistance of the thermistor at a given reference temperature, and T0 is the reference temperature.

[0008] In one technical solution of the above-mentioned design method of a μK-level temperature measurement system based on two-stage induction voltage division, the primary induction voltage divider is designed as a multi-group winding tap structure with the same number of turns, different winding combinations are selected by a first switch to determine the induction voltage division ratio, and then the voltages at A and B ends are output to realize primary coarse adjustment of the excitation voltage of the bridge; the secondary induction voltage divider is designed as M groups of winding taps with 1 turn each, and is strongly coupled with one winding tap of the primary induction voltage divider, and a second switch is used to select the first auxiliary voltage division end and the second auxiliary voltage division end to realize secondary fine adjustment; the first auxiliary voltage division end and the second auxiliary voltage division end are used for weighted superposition with the voltage division of the primary induction voltage divider; the coils of the primary induction voltage divider and the secondary induction voltage divider are connected in series, and the overall induction voltage division ratio is determined by the combination of the first switch and the second switch.

[0009] In one technical solution of the above-mentioned design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider, the coils of the primary inductive voltage divider and the secondary inductive voltage divider are connected in series. The process of jointly determining the overall inductive voltage divider ratio by a combination of the first switch and the second switch includes: when the temperature is constant and the ratio of the thermistor to the reference standard resistance is fixed, the first switch K1 is controlled by the microcontroller to select the number of turns N1 and N2 of the primary inductive voltage divider to be connected in series to one end of the bridge, where N1+N2 is the product of the number of selected groups of the primary inductive voltage divider and the number of turns p in each group, so that the bridge reaches an approximate balance; at the same time, the second switch K2 is controlled by the program to select the winding with an effective number of turns m in the secondary inductive voltage divider to be connected in series to N2 of the primary inductive voltage divider, so as to realize the program-controlled fine adjustment of the voltage divider; the two groups of inductive voltage dividers together replace the resistor network of one end of the bridge arm of the bridge.

[0010] In one technical solution of the above-mentioned design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider, the coils of the primary inductive voltage divider and the secondary inductive voltage divider are connected in series. The process of jointly determining the overall inductive voltage divider ratio through the combination of the first switch and the second switch also includes: when the temperature changes, the ratio of the thermistor to the reference standard resistor will change accordingly. At this time, the first switch is controlled by the program to adjust the turns ratio of windings N1 and N2 in the primary inductive voltage divider so that the temperature measuring bridge reaches a rough balance and ensures that the bridge can work stably under the current temperature environment; then, the second switch is controlled to assist in the adjustment of the effective number of turns of the secondary inductive voltage divider.

[0011] In one technical solution of the above-mentioned design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider, the coils of the primary inductive voltage divider and the secondary inductive voltage divider are connected in series. The process of jointly determining the overall inductive voltage divider ratio through the combination of the first switch and the second switch includes: after the states of the first switch and the second switch are selected by the program, the number of turns N1 and N2 of the primary inductive voltage divider and the effective number of turns m of the secondary inductive voltage divider are determined. At this time, the voltage divider value V1 of the inductive voltage divider bridge arm is: When adjusting the coil turns ratio to achieve basic bridge balance: Among them, R NTC R represents a thermistor. DI V represents the reference resistor, and V0 is the output voltage value of the temperature measuring bridge after inductive voltage division adjustment and signal amplification. S For AC power supply voltage, R S Represent the standard resistance; calculate the temperature sensitivity S(T) of the temperature measurement system:

[0012] In one technical solution of the above design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider, the expression for V0 is: In the formula, V0 is the bridge output voltage, and V1 is the voltage division value of the bridge arm at the inductive voltage divider, which is determined by the inductive voltage division ratio. S Powered by an AC source, R(T) is the resistance of the thermistor, R DI The reference standard resistor at the measurement end, and the differential amplification factor.

[0013] On the other hand, the present invention also provides a μK-level temperature measurement system based on a two-stage inductive voltage divider, comprising: an AC excitation source output terminal connected to the input terminal of a two-stage inductive voltage divider to provide AC power supply voltage for the entire bridge; multiple sets of winding taps of the primary inductive voltage divider connected in series, with its output terminals A and B directly connected to one end of the AC temperature measurement bridge; different combinations of turns are selected by switching a first switch to determine the primary voltage division ratio; M sets of 1-turn winding taps of the secondary inductive voltage divider are strongly coupled to one winding tap of the primary inductive voltage divider; after the coils are connected in series, the effective number of turns m is selected by switching a second switch; its output terminals CX and DX are connected to the N2 winding branch of the primary inductive voltage divider to achieve weighted superposition with the primary voltage divider, together forming an adjustable voltage divider arm of the bridge; an NTC thermistor and a reference standard resistor connected in series form the other end of the bridge. The bridge arm, which forms a symmetrical structure with the bridge arm containing the two-stage inductive voltage divider, has its connection node serving as one of the differential signal output points of the bridge. The input terminals of the differential operational amplifier are connected to the two output nodes of the bridge to amplify the weak differential signal output by the bridge. The amplified signal is then transmitted to the microcontroller. The input terminals of the analog switches are connected to different voltage divider circuits, and their output terminals are connected to the bridge branch. Switching allows for the switching of voltage divider circuits to adapt to different temperature range measurement requirements. The input terminals of the microcontroller are connected to the output terminals of the differential operational amplifier and the circuit measuring the ratio of the thermistor to the reference standard resistance. The output terminals of the microcontroller are connected to the first and second switches, and the switch states are controlled by programmable signals to achieve bridge balance adjustment. Simultaneously, the microcontroller performs temperature calculations through its internal data processing module and outputs the measurement results through the output interface.

[0014] The beneficial effects of the design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider provided by this invention are as follows: First, by constructing an AC temperature measurement bridge based on a two-stage inductive voltage divider, and utilizing an AC excitation source combined with frequency modulation and frequency domain filtering techniques, the main frequency bands of 1 / f noise and power frequency interference can be effectively avoided. This solves the problem of overlap between low-frequency slowly varying signals and noise frequency bands in traditional DC bridges, providing a foundation for μK-level temperature measurement resolution. Second, a two-stage inductive voltage divider replaces the traditional resistive voltage divider: the primary voltage divider determines the voltage division ratio through the winding turns ratio, and the secondary voltage divider achieves fine adjustment through tap selection. The combination of the two makes the voltage division ratio error less than 10%. -9Furthermore, the absence of resistor aging issues significantly improves the accuracy of voltage control at the measurement point and the long-term stability of the system. Secondly, the integrated analog switch enables flexible switching of the voltage divider circuit. Combined with the microcontroller's programmable adjustment of the two-stage voltage divider's switching state based on the real-time resistance ratio, this achieves rapid bridge balancing and adapts to wide-temperature-range measurement requirements, making it particularly suitable for dynamic monitoring of minute temperature changes, such as those related to rock thermal stress. Finally, the weak differential signal output from the bridge is amplified by a differential operational amplifier. Combined with the microcontroller's real-time data processing and temperature calculation functions, this ensures that minute temperature changes are effectively captured and accurately converted into measurement results, enhancing the system's response sensitivity and data reliability to μK-level temperature signals. Attached Figure Description

[0015] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Furthermore, similar numbers in the drawings are used to denote similar components, wherein:

[0016] Figure 1 This is a flowchart of a design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider according to an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of an AC bridge temperature measurement principle according to an embodiment of the present invention;

[0018] Figure 3 This is a temperature measurement bridge based on inductive voltage division according to an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of a high-resolution AC temperature measurement bridge with a two-stage inductive voltage divider according to an embodiment of the present invention;

[0020] Figure 5 This is a schematic diagram of a two-stage inductive voltage divider according to an embodiment of the present invention.

[0021] Figure 6 This is a temperature sensitivity diagram of the bridge output according to an embodiment of the present invention;

[0022] Figure 7 This is a noise evaluation model according to an embodiment of the present invention. Detailed Implementation

[0023] Some embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0024] like Figure 1As shown, the design method of a μK-level temperature measurement system based on a two-stage inductive voltage divider in an embodiment of the present invention mainly includes the following steps S1-S5.

[0025] Step S1: Construct an AC temperature measurement bridge based on a two-stage inductive voltage divider. Using the AC temperature measurement bridge as the basic measurement structure, suppress 1 / f noise and power frequency interference by using an AC excitation source through frequency modulation and frequency domain filtering.

[0026] In this embodiment, an AC temperature measuring bridge is used as the core measurement structure. The core design logic lies in utilizing the characteristics of the AC bridge to suppress low-frequency noise. The basic principle of the AC measuring bridge is as follows: Figure 1 As shown, when R1 / R f When the resistance is equal to R² / R(T), the bridge is balanced. R(T) is a thermistor that changes with temperature. When this condition is met, the bridge output signal is zero, and the temperature change can be inferred from the signal change that deviates from the balance. Compared with a DC bridge, an AC excitation source uses frequency modulation to shift the low-frequency slowly varying signal caused by temperature (corresponding to the resistance change) to a higher frequency band. Combined with frequency domain filtering technology, it avoids 1 / f noise (low-frequency predominance, high power spectral density). It addresses the main frequency bands of power frequency interference, fundamentally solving the problem of signal and noise frequency band overlap in traditional DC bridges, thus laying the foundation for μK-level resolution.

[0027] Step S2: Design a two-stage inductive voltage divider, wherein the two-stage voltage divider includes: a primary inductive voltage divider configured to provide excitation voltage to the bridge and including an independently set excitation winding; a secondary inductive voltage divider having multiple taps, and a variable turns ratio is formed by selecting the taps; one of the winding taps of the primary inductive voltage divider is strongly coupled to the secondary inductive voltage divider.

[0028] In this embodiment, as Figures 2-3 As shown, a two-stage inductive voltage divider design replaces the traditional resistive voltage divider, improving voltage division accuracy and stability. The primary inductive voltage divider, serving as the excitation voltage source for the bridge, includes an independent excitation winding and is designed with multiple sets of winding taps with the same number of turns. The basic voltage division ratio is determined by the turns ratio, eliminating the problem of resistor aging. The secondary inductive voltage divider has multiple taps and is strongly coupled to one winding tap of the primary voltage divider. Fine-tuning of the voltage division ratio is achieved by selecting and adjusting the effective number of turns through the tap selection. The two-stage voltage divider coils are connected in series. Through a combination of "primary coarse adjustment + secondary fine adjustment," the bridge arm voltage is precisely controlled, solving the problems of low accuracy and easy aging of traditional resistive voltage dividers, and improving the control accuracy of the voltage at the measurement point.

[0029] The output voltage of the temperature measuring bridge is as follows:

[0030]

[0031] In the implementation process, to avoid uneven coil distribution and wire diameter superposition during coil winding, and to more accurately control the inductive voltage division ratio of the bridge arms, a high-resolution AC temperature measurement bridge based on a two-stage inductive voltage division is designed here. (Schematic diagram follows.) Figure 4 As shown.

[0032] Step S3: Select an NTC thermistor as the temperature sensor.

[0033] In this embodiment, for the high-resolution AC temperature measurement bridge with inductive voltage division, in order to improve the temperature measurement accuracy of the sensor, a more sensitive NTC thermistor is selected as the temperature sensor, and its resistance value is related to the temperature change as follows: Where β is the temperature characteristic of the material, which is constant over a small temperature range; R0 is the resistance of the thermistor at a given reference temperature; and T0 is the reference temperature, typically 298.15 K.

[0034] Step S4: Integrate an analog switch, a differential operational amplifier, and a microcontroller. The analog switch is used to switch different voltage divider circuits, the differential operational amplifier amplifies the weak differential signal output by the bridge, and the microcontroller is used to program the first switch and the second switch according to the ratio of the thermistor measured in real time to the reference standard resistor to achieve bridge balance adjustment. At the same time, it processes the measurement data and completes temperature calculation and output.

[0035] In this embodiment, the bridge's programmable adjustment and signal processing are achieved through hardware integration, ensuring system automation and high precision. Analog switches are used to switch between different voltage divider circuits, and in conjunction with the tap selection of the two-stage inductive voltage divider, adapt to the voltage division ratio adjustment requirements over a wide temperature range. Differential operational amplifiers amplify the weak differential signal output by the bridge (because the voltage change corresponding to a μK-level temperature change is extremely small), with a high amplification factor. It can amplify minute signals to a processable range. Microcontroller (MCU): As the core control unit, it acquires the ratio of the NTC thermistor to the reference standard resistor in real time, and adjusts the bridge balance through programmable first and second switches; at the same time, the built-in data processing module calculates the temperature and outputs the results, realizing the automation and real-time performance of the measurement.

[0036] Figure 2 The Chinese RC oscillator serves as an AC signal source, providing a high-quality AC signal. The two-stage inductive voltage divider, consisting of an inductive voltage divider and a programmable attenuator, allows for programmable adjustment of the voltage division ratio, thereby providing a suitable output voltage value to achieve circuit balance. Assuming... Figure 2 The output voltage at terminal B in the circuit. When the temperature sensing resistor R... NTC When the ambient temperature changes, R NTC / R DI The value will change accordingly, then Figure 2 The output voltage at terminal C changes accordingly.

[0037] for Figure 4 The high-precision temperature measurement circuit has the following expression for its voltage output value V0:

[0038]

[0039] In the formula, V0 is the bridge output voltage, and V1 is the voltage division value of the bridge arm at the inductive voltage divider, which is determined by the inductive voltage division ratio. S Powered by an AC source, R(T) is the resistance of the thermistor, R DI This is the reference standard resistor for the measurement end.

[0040] In one embodiment, a two-stage inductive voltage divider circuit is designed to regulate coil accuracy, thereby achieving inductive voltage division. The primary stage provides the bridge excitation voltage and contains independent excitation windings to obtain a high-precision voltage division ratio. The secondary stage has multiple taps to provide a variable turns ratio. The two-stage inductive voltage divider design is as follows: Figure 5 As shown. The primary inductive voltage divider IVD1 is designed with multiple sets of winding taps with the same number of turns (let's say p), and one of these winding taps is strongly coupled to the secondary inductive voltage divider IVD2. IVD2 is designed with M sets of winding taps, each with 1 turn. The coils of IVD1 and IVD2 are connected in series, and the inductive voltage division ratio is determined by switches K1 and K2.

[0041] IVD1 determines the inductive voltage divider ratio via switch K1, thus determining the voltage at output terminals A and B. IVD2 determines the output auxiliary voltage divider output C via switch K2. X D X Used for weighted superposition. That is, at a certain temperature, when R... NTC / R DI With a constant ratio, the MCU software controls selector switch K1 to achieve approximate bridge balance, and programmable selector switch K2 adjusts the number of effective turns of IVD2 connected in series with IVD1, achieving programmable fine-tuning. Two sets of inductive voltage dividers replace the resistor network of one bridge arm in the bridge, reducing system resistance noise. Assume that IVD1 is selected by K1 to have turns N1 and N2 connected in series with one end of the bridge (N1 + N2 = N*p), and IVD2 is selected by K2 to have m effective turns connected in series with N2.

[0042] When the temperature changes, it can be determined according to R. NTC / R DI The program controls the first switch K1 to adjust the ratio of N1 and N2 to achieve a rough balance in the temperature measuring bridge, making the bridge work more stably under the current temperature environment. Then, the second switch K2 is used to further adjust and bring the bridge closer to balance. Through the above adjustment process, the temperature measuring system can have a wider measurement temperature threshold.

[0043] Once programs K1 and K2 are selected, the voltage divider value V1 of the inductive voltage divider bridge arm is determined.

[0044]

[0045] When the turns ratio of the coils is adjusted to make the bridge basically balanced, we have:

[0046]

[0047] Substituting equations (2) and (5) into equation (3), we can obtain the temperature sensitivity formula for the temperature measurement system:

[0048]

[0049] Step S5: Analyze the sources of circuit noise, select components based on the noise power spectrum, and combine consistency testing and metrological calibration to form a path for improving sensor performance.

[0050] In this embodiment, this step ensures that the system noise threshold meets the μK-level measurement requirements through noise control and performance calibration. Circuit noise includes resistor thermal noise, excitation source noise, etc. Low-noise components are selected based on the noise power spectrum to reduce inherent noise. Sensors and components with consistent characteristics are screened through consistency testing, and metrological calibration (such as comparing and calibrating the excitation source with a high-precision DDS signal generator) is combined to ensure that system errors are controllable, ultimately enabling the noise threshold to meet the μK-level measurement requirements.

[0051] The design of the excitation source, inductive voltage divider turns ratio, and the selection of resistors and operational amplifiers for a temperature measurement system must be evaluated based on the system's sensitivity, signal-to-noise ratio, and bridge balance. An example of parameter design is provided below for illustration.

[0052] Instance verification

[0053] Let k A =1, V S =1, B=3950, N1+N2=100, R T0 =10k, R S By taking different values, the temperature measurement sensitivity curve of the temperature measuring bridge can be obtained, such as... Figure 6 As shown, the temperature measurement system achieves maximum temperature measurement sensitivity around 20 degrees Celsius.

[0054] The key to achieving high-precision temperature measurement at the μK level is to suppress noise in the temperature measurement system and improve its signal-to-noise ratio. For example, if the sensitivity of the temperature measurement bridge is set to 0.012 V / K, and the RMS (V... S = 1V, the resolution of the designed temperature measurement system reaches The voltage noise threshold of the temperature measurement system is then...

[0055] To improve the signal-to-noise ratio of a temperature measurement system, it is necessary to analyze the noise of the temperature measurement bridge resistors, operational amplifiers, excitation source, and ripple. This can be achieved by optimizing the design of the excitation source, selecting the optimal temperature sensor, standard resistors, and low-noise operational amplifier, and thus lowering the system noise threshold. The voltage divider resistors are selected based on noise power spectrum optimization principles. A suitable temperature sensor is obtained through consistency testing and metrological calibration. Finally, the oscillator parameters are optimized by comparing the output signal of a high-precision DDS digital signal generator with the output signal of an RC oscillator.

[0056] Figure 4 The equivalent noise model of the temperature measurement system can be used Figure 7 The circuit is simplified, and the impact of circuit current noise is evaluated sequentially.

[0057] Figure 7 Temperature measurement circuit noise includes thermal noise from the op-amp input resistor. r1 Output resistor thermal noise v r2 And the input noise v of the op-amp n Input current noise i n The resistor thermal noise is calculated using the Johnson-Nyquist noise equation. The current noise through the resistor bridge and the resistor current noise at the op-amp output can be given by the following formulas:

[0058]

[0059] Where k B Boltzmann constant (1.380649 × 10⁻⁶) –23 J / K), T is the absolute temperature of resistance (Kelvin), R S and R X The resistance of the temperature measuring bridge is given by R1 and R2, which are the output resistors of the amplifier circuit. The equivalent input thermal noise of the temperature measuring circuit can be given by the following formula:

[0060]

[0061] Assume we take R T0 =10k, R S =10k, R1=R2=3k, under the condition of 20 degrees Celsius, When selecting an operational amplifier, special attention should be paid to its input noise level. n Input current noise i n Parameters. Taking TI's OPA140 operational amplifier as an example, this amplifier is a high-precision, low-noise, low-temperature-drift, low-power JFET input amplifier with a typical input voltage noise value of [value missing]. Typical input current noise value is According to Formula 9, it can be calculated that...

[0062] According to formula (3), assuming when V b =1V,k A =1, B=3950, R S =10k, R T0 =10k, When the standard resistor R s When the temperature drift value is 100ppm, a temperature change of 5μK / Hz causes a bridge output voltage error of 1.2342e-10V, introducing an error of only 0.22%, which only has an impact of 1 to 2nV on the equivalent input noise of the measurement system.

[0063] When the ambient temperature changes and the equilibrium state of the temperature-measuring bridge is disrupted, the noise and ripple of the AC power supply become significant. Using 20℃ as a reference, when RMS(V) S ) = 1V, k A =1, B=3950, R S =10k, R T0 When N = 10k and N1 = N2, calculations show that when the measurement error caused by power supply ripple and noise is equivalent to the output voltage change caused by a 5uk temperature change, the power supply error caused by power supply ripple and noise is at the level of one part per million. If the measurement value of 5μK is to be met, the error of power supply ripple and noise under this parameter should be one order of magnitude smaller than the above error.

[0064] Under the above parameters, when the temperature changes by 5 μK / √Hz, the output voltage of the measurement circuit changes by 55.5 nV / √Hz, and the bridge balance is adjusted by 1%, the measurement error caused by the 5 μK / √Hz temperature change is 0.56 nV / √Hz, which has little impact on the measurement signal-to-noise ratio.

[0065] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the original technical features, and the technical solutions resulting from these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider, characterized in that, Includes the following steps: An AC temperature measurement bridge based on a two-stage inductive voltage divider is constructed. Using the AC temperature measurement bridge as the basic measurement structure, the AC excitation source is used to suppress 1 / f noise and power frequency interference through frequency modulation and frequency domain filtering. Design a two-stage inductive voltage divider, the two-stage voltage divider comprising: a primary inductive voltage divider configured to provide excitation voltage to the bridge and including an independently configured excitation winding; a secondary inductive voltage divider having multiple taps, the selection of which forms a variable turns ratio; and one of the winding taps of the primary inductive voltage divider being strongly coupled to the secondary inductive voltage divider. An NTC thermistor was selected as the temperature sensor. The system integrates analog switches, differential operational amplifiers, and a microcontroller. The analog switches are used to switch between different voltage divider circuits, the differential operational amplifiers amplify the weak differential signal output by the bridge, and the microcontroller is used to programmatically control the first and second switches based on the ratio of the thermistor measured in real time to the reference standard resistor, so as to achieve bridge balance adjustment, while processing the measurement data and completing temperature calculation and output. By analyzing the sources of circuit noise, selecting components based on the noise power spectrum, and combining consistency testing and metrological calibration, a path for improving sensor performance is formed.

2. The method according to claim 1, characterized in that, The relationship between the resistance value of the temperature sensor and the temperature change is as follows: In the formula, β represents the temperature characteristics of the material, R0 represents the resistance of the thermistor at a given reference temperature, and T0 is the reference temperature.

3. The method according to claim 1, characterized in that, The primary inductive voltage divider is designed as a winding tap structure with multiple sets of the same number of turns. Different winding combinations are selected by the first switch to determine the inductive voltage division ratio, and then the voltage at terminals A and B is output to achieve primary coarse adjustment of the bridge excitation voltage. The secondary inductive voltage divider is designed with M groups of winding taps, each with 1 turn, forming a strong coupling with one winding tap of the primary inductive voltage divider. The output of the first auxiliary voltage divider terminal and the second auxiliary voltage divider terminal are selected by the second switch to achieve secondary fine-tuning. The first auxiliary voltage divider terminal and the second auxiliary voltage divider terminal are used to perform weighted superposition with the voltage divided by the primary inductive voltage divider. The coils of the primary inductive voltage divider and the secondary inductive voltage divider are connected in series, and the overall inductive voltage ratio is determined by a combination of the first switch and the second switch.

4. The method according to claim 3, characterized in that, The coils of the primary inductive voltage divider and the secondary inductive voltage divider are connected in series, and the process of jointly determining the overall inductive voltage ratio by combining the first switch and the second switch includes: At a constant temperature and with a fixed ratio between the thermistor and the reference standard resistor, the microcontroller controls the first switch K1 to select the number of turns N1 and N2 of the primary inductive voltage divider to be connected in series to one end of the bridge. N1 + N2 is the product of the selected number of groups of the primary inductive voltage divider and the number of turns p in each group, so that the bridge is approximately balanced. At the same time, the program controls the second switch K2 to select the winding with an effective number of turns m in the secondary inductive voltage divider to be connected in series to N2 of the primary inductive voltage divider, so as to realize the program-controlled fine adjustment of the voltage divider. The two groups of inductive voltage dividers together replace the resistor network of one end of the bridge arm of the bridge.

5. The method according to claim 3, characterized in that, The coils of the primary inductive voltage divider and the secondary inductive voltage divider are connected in series. The process of jointly determining the overall inductive voltage divider ratio by combining the first switch and the second switch also includes: when the temperature changes, the ratio of the thermistor to the reference standard resistor will change accordingly. At this time, the first switch is controlled by the program to adjust the turns ratio of windings N1 and N2 in the primary inductive voltage divider so that the temperature measuring bridge is roughly balanced and ensures that the bridge can work stably under the current temperature environment; then, the second switch is controlled to assist in the adjustment of the effective number of turns of the secondary inductive voltage divider.

6. The method according to claim 3, characterized in that, The coils of the primary inductive voltage divider and the secondary inductive voltage divider are connected in series. The process of jointly determining the overall inductive voltage division ratio by combining the first switch and the second switch includes: after the states of the first switch and the second switch are selected by the program, the number of turns N1 and N2 of the primary inductive voltage divider and the effective number of turns m of the secondary inductive voltage divider are determined. At this time, the voltage division value V1 of the inductive voltage divider bridge arm is: When adjusting the coil turns ratio to achieve basic bridge balance: Among them, R NTC R represents a thermistor. DI V represents the reference resistor, and V0 is the output voltage value of the temperature measuring bridge after inductive voltage division adjustment and signal amplification. S For AC power supply voltage, R S Indicates standard resistance; Calculate the temperature sensitivity S(T) of the temperature measurement system:

7. The method according to claim 6, characterized in that, The expression for V0 is: In the formula, V0 is the bridge output voltage, V1 is the voltage division value of the bridge arm at the inductive voltage divider, which is determined by the inductive voltage division ratio, and V S Powered by an AC source, R(T) is the resistance of the thermistor, R DI The reference standard resistor at the measurement end, and the differential amplification factor.

8. A μK-level temperature measurement system based on a two-stage inductive voltage divider, characterized in that, include: The output of the AC excitation source is connected to the input of the two-stage inductive voltage divider to provide AC power supply voltage for the entire bridge. The multiple winding taps of the primary inductive voltage divider are connected in series, and its output terminals A and B are directly connected to one end of the AC temperature measuring bridge. Different combinations of turns are selected by switching the first switch to determine the primary voltage division ratio. The M group of 1-turn winding taps of the secondary inductive voltage divider are strongly coupled to one of the winding taps of the primary inductive voltage divider. After the coils are connected in series, the effective number of turns m is selected by switching the second switch. The output terminals CX and DX of the secondary inductive voltage divider are connected to the N2 winding branch of the primary inductive voltage divider to achieve weighted superposition with the primary voltage division, which together constitutes the adjustable voltage division arm of the bridge. The NTC thermistor and the reference standard resistor are connected in series to form the other arm of the bridge. This branch forms a symmetrical structure with the arm where the two-stage inductive voltage divider is located. The connection node between the two serves as one of the differential signal output points of the bridge. The input terminals of the differential operational amplifier are connected to the two output nodes of the bridge, respectively, to amplify the weak differential signal output by the bridge. The amplified signal is then transmitted to the microcontroller. The input of the analog switch is connected to different voltage divider circuits, and the output is connected to the bridge branch. The voltage divider circuit can be switched by switching to adapt to different temperature range measurement needs. The input terminals of the microcontroller are connected to the output terminals of the differential operational amplifier and the circuit for measuring the ratio of the thermistor to the reference standard resistor, respectively. The output terminals of the microcontroller are connected to the first switch and the second switch, respectively. The switch states are controlled by the programmable control signal to achieve bridge balance adjustment. At the same time, the microcontroller completes temperature calculation through the internal data processing module and outputs the measurement results through the output interface.

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