MuK-level temperature measurement system based on secondary induction voltage division and design method

Abstract

The invention provides a muK-level temperature measurement system based on secondary induction voltage division and a design method, and the method comprises the steps: constructing an AC temperature measurement bridge based on secondary induction voltage division, taking the AC temperature measurement bridge as a basic measurement structure, and employing an AC excitation source to suppress 1 / f noise and power frequency interference through frequency modulation and frequency domain filtering; designing a two-stage inductive voltage divider; an NTC thermistor is selected as a temperature measurement sensor; an analog switch, a differential operational amplifier and a microcontroller are integrated; a circuit noise source is analyzed, elements are selected based on a noise power spectrum, and a path for improving the performance of the sensor is formed by combining consistency testing and metering calibration. The method is based on a key technology of a high-resolution alternating-current temperature measurement bridge of two-stage induction voltage division, and program-controlled voltage division is controlled by designing an analog switch, a differential operational amplifier and a microcontroller, so that a high-precision temperature measurement system with a relatively wide temperature range and a mu K-stage measurement range is realized.

Description

Technical Field

[0001] The present invention relates to the field of temperature measurement technology, and specifically provides a μK-level temperature measurement system based on two-level inductive voltage division and a design method. Background Art

[0002] Temperature measurement systems for gravitational wave detection, semiconductor chip manufacturing, and rock thermal stress observations related to earthquake prediction require micro-K-level temperature resolution. Specifically, temperature measurements onboard gravitational wave detection require resolutions of several micro-K within the 1mHz to 0.1Hz range. For earthquake prediction research, subtle temperature changes caused by rock stress before and after instability can be used to identify the sub-instability phase and thus determine the likelihood of an earthquake. Because rock thermal stress coefficients are relatively small, such as the 0.7mK / Mpa thermal stress coefficient of diorite granite, reflecting stress changes through temperature measurements requires very high resolution.

[0003] Existing temperature measurement systems have obvious limitations and are unable to meet the above requirements: DC bridge temperature measurement system: When measuring temperature changes, the resistance change caused by temperature is a low-frequency, slowly varying signal, which overlaps with the main frequency band of the widely existing 1 / f noise. It is unable to effectively suppress the influence of low-frequency error sources such as 1 / f noise and power frequency interference, which will lead to limited measurement accuracy and make it difficult to meet the temperature measurement resolution requirement of μK level. Traditional resistor voltage divider temperature measurement system: The resistor voltage divider method has the problem of resistor aging, and the accuracy of the voltage divider ratio is limited, with an error of more than 10 -9 , which will reduce the voltage control accuracy of the measuring point, affect the overall performance and measurement accuracy of the temperature measurement system, and is not conducive to achieving high-precision temperature measurement.

[0004] Therefore, a design method for a μK-level temperature measurement system based on two-level inductive pressure division is urgently needed to solve the above problems. Summary of the Invention

[0005] In order to overcome the above-mentioned drawbacks, the present invention is proposed to provide a solution or partial solution to the above-mentioned problems.

[0006] On the one hand, the present invention provides a design method for a μK-level temperature measurement system based on a two-stage inductive voltage divider, comprising the following steps: constructing an AC temperature measurement bridge based on a two-stage inductive voltage divider, taking the AC temperature measurement bridge as a basic measurement structure, and utilizing an AC excitation source to suppress 1 / f noise and power frequency interference through frequency modulation and frequency domain filtering; designing a two-stage inductive voltage divider, wherein the two-stage voltage divider comprises: a primary inductive voltage divider configured to provide an excitation voltage to the bridge, comprising an independently arranged excitation winding; a secondary inductive voltage divider having a plurality of taps, wherein a variable turns ratio is formed by selecting the taps; a winding tap of the primary inductive voltage divider is connected to a secondary inductive voltage divider; The system is strongly coupled with a first-level inductive voltage divider; an NTC thermistor is selected as a temperature sensor; an analog switch, a differential operational amplifier, and a microcontroller are integrated. The analog switch is used to switch between different voltage divider circuits, and the differential operational amplifier amplifies the weak differential signal output by the bridge. The microcontroller is used to program the first switch and the second switch according to the ratio of the thermistor to the reference standard resistor measured in real time to achieve bridge balance adjustment, while processing the measurement data to complete temperature calculation and output. The system analyzes the source of circuit noise, selects components based on the noise power spectrum, and combines consistency testing with metrological calibration to form a path to improve sensor performance.

[0007] In one technical solution of the above-mentioned design method of the μK-level temperature measurement system based on the two-stage inductive voltage division, the relationship between the resistance value of the temperature sensor and the temperature change is: Where 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 design method of the μK-level temperature measurement system based on the above-mentioned two-level inductive voltage division, the primary inductive voltage divider is designed as a structure of multiple groups of winding taps with the same number of turns. Different winding combinations are selected by the first switch to determine their inductive voltage division ratio, and then the voltages of the A and B terminals are output to achieve primary coarse adjustment of the bridge excitation voltage; the secondary inductive voltage divider is correspondingly designed as M groups of winding taps with a number of turns of 1, which form a strong coupling with a winding tap of the primary inductive voltage divider, and the first auxiliary voltage division terminal and the second auxiliary voltage division terminal are selected and output by the second switch to achieve secondary fine adjustment; the first auxiliary voltage division terminal and the second auxiliary voltage division terminal are used for weighted superposition with the voltage division of the primary inductive voltage divider; the coils of the primary inductive voltage divider and the secondary inductive voltage divider are respectively connected in series, and the overall inductive voltage division ratio is jointly determined by the combination selection of the first switch and the second switch.

[0009] In one technical solution of the above-mentioned design method of the μK-level temperature measurement system based on two-stage inductive voltage division, the coils of the primary inductive voltage divider and the secondary inductive voltage divider are respectively connected in series, and the process of jointly determining the overall inductive voltage divider ratio by the combination selection of the first switch and the second switch includes: when the temperature is constant and the ratio of the thermistor to the reference standard resistor is fixed, the microcontroller controls the first switch K1 to select the 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 selected number of groups of the primary inductive voltage divider and the number of turns p in each group, so that the bridge reaches approximate balance; at the same time, the second switch K2 is controlled by a 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, thereby achieving program-controlled fine-tuning of the voltage division; the two groups of inductive voltage divisions jointly replace the resistor network of the bridge arm at one end of the bridge.

[0010] In one technical solution of the above-mentioned design method of the μK-level temperature measurement system based on two-level inductive voltage division, the coils of the primary inductive voltage divider and the secondary inductive voltage divider are respectively connected in series, and the process of jointly determining the overall inductive voltage divider ratio by combining and selecting 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 first controlled by the program to adjust the turns ratio of the windings N1 and N2 in the primary inductive voltage divider so that the temperature measurement bridge reaches a rough balance and ensures that the bridge can operate stably in the current temperature environment; then, the effective number of turns of the secondary inductive voltage divider is auxiliary controlled by controlling the second switch.

[0011] In one technical solution of the above-mentioned design method of the μK-level temperature measurement system based on two-stage inductive voltage division, the coils of the primary inductive voltage divider and the secondary inductive voltage divider are respectively connected in series, and the process of jointly determining the overall inductive voltage division ratio by selecting the combination of the first switch and the second switch includes: when the states of the first switch and the second switch are selected by the program, the turns N1 and N2 of the primary inductive voltage divider and the effective turns m of the secondary inductive voltage divider are determined, and the voltage division value V1 of the bridge arm of the inductive voltage divider end is then: When the coil turns ratio is adjusted to make the bridge basically balanced: Among them, R NTC Represents thermistor, R DI Represents the reference resistance, V0 is the output voltage value of the temperature measuring bridge after the induction voltage division adjustment and signal amplification, V S is the AC source supply voltage, R S Represents the standard resistance; calculate the temperature sensitivity S(T) of the temperature measurement system:

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

[0013] On the other hand, the present invention also provides a μK-level temperature measurement system based on two-level inductive voltage divider, including: the output end of the AC excitation source is connected to the input end of the two-level inductive voltage divider to provide AC power supply voltage for the entire bridge, multiple groups of winding taps of the primary inductive voltage divider are connected in series, and its output ends A and B are directly connected to one end of the bridge arm of the AC temperature measurement bridge. Different turns combinations are selected by switching the first switch to determine the primary voltage divider ratio, and the M groups of 1-turn winding taps of the secondary inductive voltage divider are strongly coupled with 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, and its output ends 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, and together constitute the adjustable voltage divider arm of the bridge; the NTC thermistor and the reference standard resistor are connected in series to form the other end of the bridge. The bridge arm forms a symmetrical structure with the bridge arm where the two-stage inductive voltage divider is located, and the connection node between the two serves as one of the differential signal output points of the bridge; the input end of the differential operational amplifier is respectively connected to the two output nodes of the bridge, for amplifying the weak differential signal output by the bridge, and the amplified signal is transmitted to the microcontroller; the input end of the analog switch is connected to different voltage-dividing circuits, and the output end is connected to the bridge branch, and the voltage-dividing circuit is switched by switching to meet the measurement requirements of different temperature ranges; the input end of the microcontroller is respectively connected to the output end of the differential operational amplifier and the ratio measurement circuit of the thermistor and the reference standard resistor, and the output end of the microcontroller is respectively connected to the first switch and the second switch, and the switch state is controlled by the program-controlled signal to realize the balance adjustment of the bridge; at the same time, the microcontroller completes the temperature calculation through the internal data processing module, and outputs the measurement results through the output interface.

[0014] The beneficial effects of the design method of a μK-level temperature measurement system based on two-stage inductive voltage division provided by the present invention are as follows: First, by constructing an AC temperature measurement bridge based on two-stage inductive voltage division and utilizing an AC excitation source combined with frequency modulation and frequency domain filtering technology, the main frequency bands of 1 / f noise and power frequency interference can be effectively avoided, solving the problem of overlapping low-frequency slow-changing signals and noise frequency bands in traditional DC bridges, and providing a foundation for μK-level temperature measurement resolution. Secondly, a two-stage inductive voltage divider is used to replace the traditional resistive voltage divider: the primary voltage divider determines the voltage divider ratio by the winding turns ratio, and the secondary voltage divider achieves fine adjustment by tap selection. The combination of the two makes the voltage divider ratio error less than 10 -9, and there is no resistance aging problem, which significantly improves the voltage control accuracy of the ratio measurement point and the long-term stability of the system. Second, the integrated analog switch realizes flexible switching of the voltage divider circuit, and the microcontroller adjusts the switch state of the two-stage voltage divider according to the real-time resistance ratio, which can realize rapid balance of the bridge and adapt to wide-temperature-range measurement requirements, especially for dynamic monitoring of small temperature changes of rock thermal stress. Finally, by amplifying the weak differential signal output by the bridge with a differential operational amplifier, and combining the real-time data processing and temperature calculation functions of the microcontroller, the system ensures that small temperature changes are effectively captured and accurately converted into measurement results, improving the response sensitivity and data reliability of the system to μK-level temperature signals. BRIEF DESCRIPTION OF DRAWINGS

[0015] The disclosure of the present application will become more fully understood from the detailed description given herein below, and appended claims, accompanied by the accompanying drawings. It is to be understood that the drawings are only for the purpose of illustration, and are not intended to limit the scope of the present application. In addition, similar reference numerals are used to indicate similar components in the figures, wherein:

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

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

[0018] Figure 3 is an inductive voltage division-based temperature measurement bridge according to an embodiment of the present application;

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

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

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

[0022] Figure 7 is a noise evaluation model according to an embodiment of the present application. DETAILED DESCRIPTION

[0023] Some embodiments of the present application will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application, and are not intended to limit the protection scope of the present application.

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

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

[0026] In this embodiment, the AC temperature measurement bridge is used as the core measurement structure, and the core design logic is to use the characteristics of the AC bridge to suppress low-frequency noise. The basic principle of the AC measurement bridge is as follows: Figure 1 As shown, when R1 / R f =R2 / R(T), the bridge reaches equilibrium. For a thermistor with R(T) varying with temperature, when this condition is met, the bridge output signal is zero, and the temperature change can be inferred by the signal change that deviates from the equilibrium. Compared with the DC bridge, the AC excitation source transfers the low-frequency slow-changing signal (corresponding to the resistance change) caused by temperature to the high frequency band through frequency modulation, and then combines with frequency domain filtering technology to avoid 1 / f noise (low frequency dominant, power spectrum density The main frequency bands of signal and noise interference are solved in principle, which solves the problem of signal and noise frequency band overlap in traditional DC bridge and lays the foundation for μK level resolution.

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

[0028] In this embodiment, Figures 2-3 As shown in the figure, the collaborative design of the two-stage inductive voltage divider replaces the traditional resistive voltage divider to improve the voltage division accuracy and stability. Primary inductive voltage divider: As the excitation voltage source of the bridge, it contains an independent excitation winding and is designed as multiple sets of winding taps with the same number of turns. The basic voltage division ratio is determined by the turns ratio, and there is no problem of resistor aging. Secondary inductive voltage divider: Multiple taps are set, which are strongly coupled with a winding tap of the primary voltage divider. The effective number of turns is adjusted by tap selection to achieve fine tuning of the voltage division ratio. The two-stage voltage divider coils are connected in series, and the bridge arm voltage is accurately controlled through the combined control of "primary coarse adjustment + secondary fine adjustment", which solves the problems of low accuracy and easy aging of traditional resistive voltage dividers and improves the voltage control accuracy of the ratio measurement point.

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

[0030]

[0031] In the implementation process, in order to avoid the problems of uneven coil distribution and wire warp superposition during coil winding and to more accurately control the bridge arm induction voltage ratio, a high-resolution AC temperature measurement bridge based on two-level induction voltage is designed. Figure 4 shown.

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

[0033] In this embodiment, for the high-resolution AC temperature measurement bridge that senses voltage division, in order to improve the temperature measurement accuracy of the sensor, an NTC thermistor with higher sensitivity is selected as the temperature measurement sensor. The relationship between its resistance value and temperature change is: Where β is the temperature characteristic of the material and 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 298.15K.

[0034] Step S4: Integrate an analog switch, a differential operational amplifier, and a microcontroller, wherein the analog switch is used to switch between 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 to the reference standard resistor measured in real time to achieve bridge balance adjustment, and simultaneously process the measurement data to complete temperature calculation and output.

[0035] In this embodiment, the programmable adjustment and signal processing of the bridge are realized through hardware integration to ensure system automation and high precision. Analog switch: used to switch different voltage divider circuits, and cooperate with the tap selection of the two-stage inductive voltage divider to adapt to the voltage divider ratio adjustment requirements within a wide temperature range. Differential op amp: amplifies the weak differential signal output by the bridge (because the voltage change corresponding to the μK level temperature change is extremely small), and its amplification factor is The microcontroller (MCU) acts as the core control unit, collecting the ratio of the NTC thermistor to the reference resistor in real time and adjusting the bridge balance by programmable first and second switches. Simultaneously, the built-in data processing module calculates the temperature and outputs the result, achieving automated and real-time measurement.

[0036] Figure 2 The Chinese RC oscillator is used as an AC signal source to provide a high-quality AC signal source. The two-stage inductive voltage divider composed of the inductive voltage divider and the programmable attenuator can programmatically adjust the inductive voltage divider ratio, thereby providing a suitable output voltage value to achieve circuit balance. Assume that Figure 2 The output voltage of terminal B is NTC When the ambient temperature changes, R NTC / R DI The value of will change accordingly. Figure 2 The output voltage of the C terminal changes accordingly.

[0037] For Figure 4 The expression of the voltage output value V0 of the high-precision temperature measurement circuit is:

[0038]

[0039] In the formula, V0 is the output voltage of the bridge, V1 is the voltage of the bridge arm at the sensing voltage dividing end, which is determined by the sensing voltage dividing ratio. V S is supplied by an AC source, R(T) is the resistance of the thermistor, and R DI is the reference standard resistance at the measurement end.

[0040] In an embodiment, a two-stage sensing voltage dividing circuit is designed to regulate the precision of the coil, thereby achieving sensing voltage division. The primary stage is used to provide a bridge excitation voltage and contains independent excitation windings to obtain a high-precision voltage dividing ratio, and the secondary stage contains multiple taps to provide a variable number of turns ratio. The two-stage sensing voltage divider is designed as shown in Figure 5 . In the design, the primary sensing voltage divider IVD1 is designed as multiple groups of winding taps with the same number of turns (assuming the number of turns is p), and one of the winding taps is strongly coupled with the secondary sensing voltage divider IVD2, which is designed as M groups of winding taps with one turn. The coils of IVD1 and IVD2 are connected in series, and the sensing voltage dividing ratio is determined by selecting switches K1 and K2.

[0041] IVD1 determines the output voltage at terminals A and B by selecting the switch K1, and IVD2 determines the auxiliary voltage dividing output C X , D X for weighted superposition. That is, at a certain temperature, when the R NTC / R DI ratio is constant, the switch K1 is selected by MCU software control to achieve approximate balance of the bridge, and the switch K2 is programmed to adjust the effective number of turns of IVD2 connected to IVD1, thereby achieving program-controlled fine tuning. The two groups of sensing voltage dividers replace the resistance network of one end of the bridge arm, thereby reducing the system resistance noise. Assuming that IVD1 is selected by K1 to achieve IVD1 turn selection as N1 and N2 connected to one end of the bridge (N1+N2=N*p), and IVD2 is selected by K2 to achieve effective turn selection as m connected to N2.

[0042] When the temperature changes, the R NTC / R DI ratio can be used to adjust the ratio of N1 and N2 by program control of the first switch K1 to achieve approximate balance of the temperature measurement bridge, so that the temperature measurement bridge works more stably at the current temperature environment; and the second switch K2 is used to assist in regulation to achieve more approximate balance of the bridge. Through the above regulation process, the temperature measurement system has a wider measurement temperature threshold.

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

[0044]

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

[0046]

[0047] Substituting equations (2) and (5) into equation (3), the temperature sensitivity formula of the temperature measurement system can be obtained:

[0048]

[0049] Step S5: Analyze the source of circuit noise, select components based on the noise power spectrum, and combine consistency testing and metrological calibration to form a path to improve 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, and other factors. Low-noise components are selected based on the noise power spectrum to reduce inherent noise. Consistent sensors and components are screened through consistency testing. Combined with metrological calibration (such as comparing and calibrating the excitation source with a high-precision DDS signal generator), this ensures that system errors are controllable and ultimately ensures that the noise threshold meets the μK-level measurement requirements.

[0051] The design of the temperature measurement system's excitation source, inductive voltage divider turns ratio, and resistor and operational amplifier parameters must be evaluated based on the system's sensitivity, signal-to-noise ratio, and bridge balance. The following provides an example of parameter design to illustrate this.

[0052] Example verification

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

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

[0055] Improving the signal-to-noise ratio of the temperature measurement system requires analyzing the temperature bridge resistor noise, operational amplifier noise, excitation source noise, and ripple. By selecting the optimal temperature sensor, standard resistor, and low-noise operational amplifier, and optimizing the excitation source design to achieve the aforementioned system noise threshold, the voltage divider resistors are selected based on the noise power spectrum optimization principle. The optimal temperature sensor is obtained through consistency testing and metrological calibration. The oscillator parameters are optimized by comparing the output signal of a high-precision DDS digital signal generator with that of an RC oscillator.

[0056] Figure 4 The equivalent noise model of the temperature measurement system is available Figure 7 The circuit is simplified and the influence of circuit current noise is evaluated one by one.

[0057] Figure 7 The temperature measurement circuit noise includes the thermal noise of the op amp input resistor v r1 , output resistance thermal noise v r2 , and the op amp’s input noise v n , input current noise i n The thermal noise of the resistor is calculated using the Johnson-Nyquist noise equation. The current noise through the resistor bridge and the resistor current noise at the output of the op amp can be given by the following formula:

[0058]

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

[0060]

[0061] Assume that R T0 =10k, R S =10k, R1=R2=3k, at 20 degrees Celsius, When selecting an operational amplifier, special attention should be paid to the input noise v 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. Its input voltage noise is typically The typical input current noise is According to formula 9,

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

[0063] When the ambient temperature changes and the temperature bridge balance is destroyed, the influence of the noise and ripple of the AC power supply cannot be ignored. Taking 20℃ as the reference, when RMS(V S )=1V,k A =1, B=3950, R S =10k, R T0 =10k, N1=N2, it has been measured that when the measurement error caused by power supply ripple and noise is equivalent to the output voltage change caused by 5uk temperature change, the power supply error caused by power supply ripple and noise is at the level of one millionth. If the measurement value of 5μK is to be met, then for this parameter, the error of power supply ripple and noise should be one order of magnitude smaller than the above error.

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

[0065] Thus far, the technical solutions of the present invention have been described in conjunction with 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 may make equivalent changes or substitutions to the original technical features, and the technical solutions after such changes or substitutions will 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 pressure divider, characterized in that: The following steps are involved: Constructing an AC temperature measurement bridge based on a two-stage inductive voltage divider, using the AC temperature measurement bridge as the basic measurement structure, and using an AC excitation source to suppress 1 / f noise and power frequency interference through frequency modulation and frequency domain filtering; A two-stage inductive voltage divider is designed, comprising: a primary inductive voltage divider configured to provide an excitation voltage to a bridge, comprising an independently arranged excitation winding; a secondary inductive voltage divider having a plurality of taps, wherein a variable turns ratio is formed by selecting the taps; and one winding tap of the primary inductive voltage divider is strongly coupled to the secondary inductive voltage divider. Select NTC thermistor as the temperature sensor; An integrated analog switch, a differential operational amplifier, and a microcontroller are included. The analog switch is used to switch between 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 and second switches based on the ratio of the thermistor to the reference standard resistor measured in real time to achieve bridge balance adjustment. The microcontroller also processes the measurement data to complete temperature calculation and output. Analyze circuit noise sources, select components based on the noise power spectrum, and combine consistency testing and metrological calibration to form a path to improve sensor performance.

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: Where 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.

3. The method according to claim 1, characterized in that The primary inductive voltage divider is designed as a structure with multiple groups of winding taps with the same number of turns. Different winding combinations are selected by the first switch to determine the inductive voltage divider ratio, and then the voltages at the A and B terminals are output to achieve primary coarse adjustment of the bridge excitation voltage. The secondary inductive voltage divider is correspondingly designed as M groups of winding taps each having 1 turn, forming a strong coupling with a winding tap of the primary inductive voltage divider. The second switch selectively outputs a first auxiliary voltage divider terminal and a second auxiliary voltage divider terminal to achieve secondary fine-tuning. The first auxiliary voltage divider terminal and the second auxiliary voltage divider terminal are used for weighted superposition with the divided voltage of the primary inductive voltage divider. The coils of the primary inductive voltage divider and the secondary inductive voltage divider are respectively connected in series, and the overall inductive voltage division ratio is jointly determined by the combination selection 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 a process of jointly determining the overall inductive voltage divider ratio by selecting 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 resistor is fixed, the microcontroller controls the first switch K1 to select the turns N1 and N2 of the primary inductive voltage divider and connect them in series to one end of the bridge (where 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 reaches 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 and connect it in series to N2 of the primary inductive voltage divider, achieving program-controlled fine-tuning of the voltage divider. The two sets of inductive voltage dividers jointly replace the resistor network of one end of the bridge arm.

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, and the process of jointly determining the overall inductive voltage divider ratio by combining and selecting 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 first controlled by the program to adjust the turns ratio of the windings N1 and N2 in the primary inductive voltage divider so that the temperature measurement bridge reaches a rough balance and ensures that the bridge can operate stably in the current temperature environment; then, the second switch is controlled to assist in regulating 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, and the overall inductive voltage divider ratio is determined by selecting a combination of the first switch and the second switch. The process includes: when the states of the first switch and the second switch are selected by the program, the turns N1 and N2 of the primary inductive voltage divider and the effective 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 the coil turns ratio is adjusted to make the bridge basically balanced: Among them, R NTC Represents thermistor, R DI Represents the reference resistance, V0 is the output voltage value of the temperature measuring bridge after the induction voltage division adjustment and signal amplification, V S is the AC source 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 of V0 is: Where V0 is the bridge output voltage, V1 is the voltage divider value of the inductive voltage divider end, which is determined by the inductive voltage divider ratio. S is the AC power source, R(T) is the thermistor resistance, R DI is the reference standard resistance of the measurement end, the differential end amplification factor 8. A μK-level temperature measurement system based on two-stage inductive pressure division, characterized in that: include: The output end of the AC excitation source is connected to the input end of the two-stage inductive voltage divider to provide an AC power supply voltage for the entire bridge. Multiple groups of winding taps of the primary inductive voltage divider are connected in series, and its output ends A and B are directly connected to one end of the bridge arm of the AC temperature measurement bridge. Different combinations of turns are selected by switching the first switch to determine the primary voltage divider ratio. The M groups of 1-turn winding taps of the secondary inductive voltage divider are strongly coupled with 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 ends 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 divider, together forming an adjustable voltage divider arm of the bridge. The NTC thermistor and the reference standard resistor are connected in series to form the other end of the bridge arm. This branch forms a symmetrical structure with the bridge 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 respectively connected to the two output nodes of the bridge, and are used to amplify the weak differential signal output by the bridge. The amplified signal is then transmitted to the microcontroller. The input end of the analog switch is connected to different voltage divider circuits, and the output end is connected to the bridge branch. By switching, the voltage divider circuit can be switched to meet the measurement requirements of different temperature ranges. The input end of the microcontroller is respectively connected to the output end of the differential operational amplifier and the ratio measurement circuit of the thermistor and the reference standard resistor. The output end of the microcontroller is respectively connected to the first switch and the second switch. The switch state is controlled by the program-controlled 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.

Images