Temperature measurement system and temperature measurement method based on optimized single-arm bridge and interactive digital filtering

Abstract

The invention discloses a temperature measurement system and a temperature measurement method based on an optimized single-arm bridge and interactive digital filtering, and belongs to the technical field of sensor signal precision measurement. According to the invention, the problems of low accuracy, poor real-time performance and high complexity of a traditional temperature measurement method based on a single-arm bridge are solved. According to the invention, through the optimization design of the resistance value of the resistor on the bridge arm of the single-arm bridge, the output nonlinearity can be effectively inhibited and the sensitivity can be improved; an AD7608 analog-to-digital converter is adopted to synchronously acquire the output of a constant voltage source and the voltage difference between a first measurement bridge arm reference point and a second measurement bridge arm reference point so as to eliminate an asynchronous sampling error caused by asynchronous signal sampling; the accidental error of the sampling value, the random error of the sampling value and the inherent deviation of the temperature measurement value are effectively inhibited through filtering processing, and the error introduction caused by a complex operation process is avoided through directly solving the high-precision temperature measurement value. The method can be applied to the field of temperature measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of precise measurement of sensor signals, and particularly relates to a temperature measurement system and a temperature measurement method based on an optimized single-arm bridge and interactive digital filtering. Background Technique

[0002] Temperature is a physical parameter characterizing the hot and cold state of an object, and its level directly affects the characteristics of the object. Therefore, accurate temperature measurement has always been an important research direction in the field of instruments and meters. The platinum resistance PT1000 has the advantages of high precision, large measurement range, good repeatability, etc., which lays a good hardware foundation for accurately detecting weak changes in the target temperature. Therefore, the temperature weak signal detection method based on the platinum resistance PT1000 is widely used in precise temperature measurement methods. Obtaining high temperature measurement accuracy in a large temperature measurement range is an important research direction in the field of precise temperature measurement, and the key lies in the selection of a high-sensitivity measurement circuit and the elimination of inherent errors. The single-arm bridge has a high ability to detect weak resistance value changes, but its output non-linearity will, to a certain extent, increase the complexity of the temperature measurement value calculation model and reduce the accuracy and reliability of precise temperature measurement; the output voltage of the constant voltage source that excites the single-arm bridge fluctuates, which will cause the output sampling moment and the excitation moment of the single-arm bridge to be asynchronous, thereby introducing asynchronous sampling errors; untimely processing of the temperature measurement sampling value will cause sampling errors and slow down the convergence speed of the temperature measurement value, resulting in the inability to accurately and real-time output the temperature measurement value. Therefore, a precise temperature measurement circuit with wide range and fast convergence characteristics is an important way to improve the accuracy and reliability of precise temperature measurement, and accurate data processing of the temperature measurement value is an important guarantee for the accuracy and reliability of precise temperature measurement. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems of low accuracy, poor real-time performance and high complexity of the traditional temperature measurement method based on a single-arm bridge, and to propose a temperature measurement system and a temperature measurement method based on an optimized single-arm bridge and interactive digital filtering.

[0004] The technical solution adopted by the present invention to solve the above technical problems is:

[0005] Based on one aspect of the present invention, a temperature measurement system based on an optimized single-arm bridge and interactive digital filtering, the system includes a single-arm bridge, a differential amplifier, an analog-to-digital converter, a resistance calculation module, a resistance processing module, a temperature calculation module and a temperature correction module; wherein:

[0006] The single-arm bridge includes a constant voltage source, a first measurement bridge arm and a second measurement bridge arm. The first measurement bridge arm includes resistors R1 and R3, and the second measurement bridge arm includes resistors R2 and R4. The resistor R4 in the single-arm bridge is used as the sensing resistor of the target temperature;

[0007] The voltages of the reference points of the first measurement bridge arm and the second measurement bridge arm are input into a differential amplifier, and an analog-to-digital converter is used to synchronously collect the voltage of the constant voltage source and the output voltage of the differential amplifier;

[0008] The resistance calculation module is used to calculate the value of resistor R4 according to the sampling result of the analog-to-digital converter;

[0009] The resistance processing module is used to process the value of resistor R4, and the temperature calculation module is used to calculate the target temperature T′ according to the processed value of resistor R4;

[0010] The temperature correction module is used to correct the calculated target temperature T′ to obtain the corrected target temperature, that is, to obtain the temperature detection result.

[0011] Based on another aspect of the present invention, a temperature measurement method based on an optimized single-arm bridge and interactive digital filtering, the method specifically includes the following steps:

[0012] Step 1: Use the resistor R4 in the second measurement bridge arm of the single-arm bridge as a temperature sensor to sense the target temperature;

[0013] Step 2: Use the constant voltage source DC to excite the single-arm bridge, take the voltages of the reference points on the first measurement bridge arm and the second measurement bridge arm as the inputs of the differential amplifier, and use the analog-to-digital converter to synchronously sample the voltage of the constant voltage source and the output voltage of the differential amplifier. Denote the sampled output voltage of the differential amplifier as U(t), and denote the sampled voltage of the constant voltage source as U;

[0014] Step 3: Calculate the resistance value of R4 using the sampled U(t) and U, process the calculated resistance value, and then calculate the target temperature T′ based on the processed resistance;

[0015] Step 4: Correct the target temperature T′ calculated in Step 3 to obtain the final target temperature detection result.

[0016] The beneficial effects of the present invention are:

[0017] Through the optimized design of the resistance values on the arms of the single-arm bridge, the present invention can effectively suppress the output non-linearity and improve the sensitivity to enhance the temperature measurement accuracy. The AD7608 analog-to-digital converter is used to synchronously collect the output of the constant voltage source and the voltage difference between the reference points of the first measurement bridge arm and the second measurement bridge arm to eliminate the asynchronous sampling error caused by the asynchronous signal sampling, further enhancing the temperature measurement accuracy. Through the filtering process, the accidental error of the sampling value, the random error of the sampling value, and the inherent deviation of the temperature measurement value are effectively suppressed. By directly obtaining the high-precision temperature measurement value, the error introduced by the complex operation process is avoided. Thus, while improving the accuracy of the temperature measurement value, the rapid convergence and real-time output of the temperature measurement value are ensured, effectively expanding the application of the precise temperature measurement method in the field of precise temperature detection.

[0018] The method of the present invention can achieve precise temperature measurement with a temperature measurement accuracy of ±0.001 °C and a temperature measurement range of approximately 0 °C to 118 °C, realizing high sensitivity, high accuracy, and a wide temperature measurement range in temperature measurement. Description of the Drawings

[0019] Figure 1 is a flowchart of a temperature measurement method based on an optimized single-arm bridge and interactive digital filtering of the present invention;

[0020] Figure 2a is a schematic diagram of a traditional single-arm bridge circuit;

[0021] Figure 2b is a schematic diagram of a traditional resistance comparison method;

[0022] Figure 3 is a schematic diagram of a temperature measurement circuit based on a single-arm bridge adopted by the present invention;

[0023] Figure 4 is a curve graph of the value of f(R) when R0 ∈ [0, 10 kΩ];

[0024] Figure 5 is a curve graph of the value of g(R) when R0 ∈ [0, 10 kΩ];

[0025] Figure 6 is the simulation result of the output voltage of the temperature measurement circuit;

[0026] Figure 7 is the simulation result of the output voltage increment of the temperature measurement circuit;

[0027] Figure 8 is the asynchronous measurement error under the excitation of the output of the constant voltage source with an accuracy error of ±1%;

[0028] Figure 9 is the filtering effect diagram of the temperature measurement data;

[0029] Figure 10is the temperature measurement curve at 10.014 °C;

[0030] Figure 11 is the temperature measurement curve at 52.244 °C;

[0031] Figure 12 is the temperature measurement curve at 87.603 °C. Specific implementation manners

[0032] Theoretical basis

[0033] The output characteristics of the temperature measurement circuit include output non-linearity and sensitivity. The output non-linearity characterizes the mathematical relationship between the output response and the input. Significant output non-linearity increases the difficulty of solving the measurement signal, and reducing the output non-linearity is a necessary means to improve the accuracy of the temperature measurement signal; sensitivity refers to the ability to measure the minimum change value of the measurement signal. High sensitivity indicates a strong ability to detect weak signal changes, and effectively improving the sensitivity is the fundamental way to improve the measurement accuracy. The output non-linearity r L and sensitivity K u have the following mathematical expressions:

[0034]

[0035] In the formula, u is the output of the temperature measurement circuit, u' is the linear value of the output u of the temperature measurement circuit, r is the input resistance, and Δr is the resistance change value of the input resistance r. Traditional temperature measurement circuits include single-arm bridges and resistance comparison methods, which are introduced as follows:

[0036] (1) Single-arm bridge

[0037] The single-arm bridge inversely calculates the target resistance value by measuring the voltage difference induced by the non-equilibrium bridge arm resistance. As Figure 2a shown is the schematic diagram of the traditional temperature measurement circuit based on a single-arm bridge. R1, R2, and R3 are all bridge arm resistances, R4 is the standard resistance value of the physical quantity x under certain conditions, R4 ∝ (x), A F is a differential amplifier, and DC is a constant voltage source with an output voltage of U. R1 and R3 form measurement bridge arm 1, and R2 and R4 form measurement bridge arm 2. DC drives measurement bridge arm 1 and measurement bridge arm 2. The output U(t) of the signal precision measurement method based on a single-arm bridge can be expressed as:

[0038]

[0039] When the target physical quantity x changes and the resistance change amount is ΔR4, the output U0 of the single-arm bridge can be expressed as:

[0040]

[0041] In the formula, n = R2 / R4 = R1 / R3. As shown in Equation (1), the output non-linearity r of the single-arm bridgeL 0 As shown below:

[0042]

[0043] If the target physical quantity x has a slight change relative to R4 and the change in resistance value is ΔR4, the output nonlinearity r of the single-arm bridge L 0 increases. Let r L 0 be differentiated with respect to n, and its derivative is expressed as:

[0044]

[0045] r L 0 is an increasing function with n as the independent variable. Selecting an appropriate n can effectively suppress the output nonlinearity. As shown in Equation (1), the sensitivity K of the single-arm bridge u 0 is as follows:

[0046]

[0047] It can be seen from Equation (6) that as n increases, the sensitivity K u 0 significantly decreases.

[0048] Let K u 0 be differentiated with respect to n, and its derivative can be expressed as:

[0049]

[0050] When n = 1, K u 0 takes the maximum value, that is, K u 0 = U / 4; when n > 1, K u 0 decreases with the increase of n; when 0 < n < 1, K u 0 increases with the increase of n. Therefore, an appropriate n can effectively improve K u 0 .

[0051] (2) Resistance comparison method

[0052] The resistance comparison method realizes accurate measurement of the resistance value of the target physical quantity x under certain conditions by comparing resistances. The schematic diagram of the traditional temperature measurement circuit based on the resistance comparison method is as Figure 2bAs shown in the figure. R5 is a reference resistor, and R6 is the resistance value of the target physical quantity x under certain conditions, and R6 ∝ (x). R5 and R6 form a measurement loop and are driven by a constant voltage source DC. When the target physical quantity x changes and the change in resistance value is ΔR6, the output U1 of the signal precision measurement method based on the resistance value comparison method can be expressed as:

[0053]

[0054] In the formula, n′ = R5 / R6. As shown in formula (1), the output non-linearity r of the resistance value comparison method L 1 and the sensitivity K u 1 are as follows:

[0055]

[0056] It can be seen from formula (9) and formula (10) that r L 0 and r L 1 have the same mathematical expression and there is output non-linearity. An appropriate resistance ratio can effectively suppress the output non-linearity; it can be seen from formula (6) and formula (10) that K u 1 and K u 0 have the same mathematical expression and the amplitude is related to the resistance ratio. Since the measurement principles of the single-arm bridge and the resistance value comparison method are different and the resistance ratios of the measurement circuits are different, according to experience, n ≤ n′. At this time, K u 1 <K u 0 . Based on this, it can be concluded that the single-arm bridge can more accurately detect weak changes in the target signal, and giving full play to the sensitivity and effectively limiting the output non-linearity are important ways to achieve precise temperature measurement.

[0057] Specific implementation method 1: Combine Figure 1 to illustrate this implementation method. A temperature measurement system based on an optimized single-arm bridge and interactive digital filtering described in this implementation method includes a single-arm bridge, a differential amplifier, an analog-to-digital converter, a resistance calculation module, a resistance processing module, a temperature calculation module, and a temperature correction module; among them:

[0058] The single-arm bridge includes a constant voltage source, a first measurement bridge arm, and a second measurement bridge arm. The first measurement bridge arm includes resistors R1 and R3, and the second measurement bridge arm includes resistors R2 and R4. The resistor R4 in the single-arm bridge is used as the sensing resistor for the target temperature (that is, the resistor R4 is used as the temperature measurement sensor);

[0059] The voltages of the reference points of the first measurement bridge arm and the second measurement bridge arm are input into a differential amplifier, and an analog-to-digital converter is used to synchronously collect the voltage of the constant voltage source and the output voltage of the differential amplifier;

[0060] The present invention uses an 18-bit analog-to-digital converter AD7608 to synchronously sample the output of the temperature measurement circuit and the output of the constant voltage source that excites the single-arm bridge, so as to suppress the asynchronous measurement error caused by the output fluctuation of the constant voltage source that excites the single-arm bridge;

[0061] The resistance calculation module is used to calculate the value of resistor R4 according to the sampling result of the analog-to-digital converter;

[0062] The resistance processing module is used to process the value of resistor R4, and the temperature calculation module is used to calculate the target temperature T′ according to the processed value of resistor R4;

[0063] The temperature correction module is used to correct the calculated target temperature T′ to obtain the corrected target temperature, that is, to obtain the temperature detection result.

[0064] As Figure 3 shown, different bridge arm resistors induce different output nonlinearities and sensitivities of the single-arm bridge. It is known that the weak signal change is directly reflected by the differential voltage between the bridge arms. Assuming that R1, R2, R3, and R4 generate resistance changes ΔR1, ΔR2, ΔR3, and ΔR4, R1 and R4 should increase and R2 and R3 should decrease, then

[0065] R1′ = R1 + ΔR1 R2′ = R2 - ΔR2 R3′ = R3 - ΔR3 R4′ = R4 + ΔR4 (11)

[0066] wherein, R1′, R2′, R3′, and R4′ are the bridge arm resistors after the resistance change. At this time, the output U2 of the single-arm bridge can be expressed as:

[0067]

[0068] Based on this, its output nonlinearity r L 3 is as follows:

[0069]

[0070] r L 3 The necessary condition for the amplitude to decrease is that the amplitude of the numerator decreases or the amplitude of the denominator increases, that is, the amplitudes of ΔR2 and ΔR3 decrease. When ΔR2 = 0 and ΔR3 = 0, the amplitude of r L 3 is the minimum value, then there is:

[0071]

[0072] Therefore, the bridge output U3 can be expressed as:

[0073]

[0074] At this time, the bridge sensitivity K u 3 is as follows:

[0075]

[0076] If R2 and R3 remain unchanged, when R1 and the target resistor R4 with the same characteristic change at different and asymmetric positions of the bridge arms, the non - linear output of the single - arm bridge is effectively suppressed and the sensitivity is doubled. R1 can be replaced by the target resistor R4. Figure 3 That is the high - sensitivity and wide - temperature - measurement - range temperature - measurement circuit proposed by the present invention.

[0077] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that both the resistor R1 and the resistor R4 are platinum resistors PT1000; R2 = R3 = R0, where R0 represents the resistance value of the platinum resistor PT1000 when the target temperature is 0 °C.

[0078] Its steps and parameters are the same as those in Specific Embodiment 1.

[0079] Based on the resistance value optimization of the bridge arms of the single - arm bridge, the present invention can effectively suppress the non - linear output characteristics of the single - arm bridge and improve the measurement sensitivity, ensuring a linear relationship between "input resistance - output voltage" to simplify the complexity of the temperature - measurement calculation model, and further ensuring the improvement of temperature - measurement accuracy.

[0080] When the target temperature T changes linearly, U(t) shows a non - linear change. The simpler the corresponding relationship between the target temperature T and U(t), the simpler the temperature - measurement value calculation model, the smaller the calculation error, and the higher the temperature - measurement accuracy. Therefore, appropriately selecting the bridge - arm resistance value in combination with the application scenario to suppress the output non - linearity is an important prerequisite for improving temperature - measurement accuracy. Usually, a platinum resistor is used as the temperature - measurement sensor in the temperature - measurement system, and its resistance R t is as follows:

[0081] R t = R0(1 + AT + BT 2 ) (17)

[0082] In the formula, A, B, and R0 are platinum - resistor parameters. Let R1 = R4 = R t , Equation (2) can be further expressed as:

[0083]

[0084] In the formula, C = R2 / R0, D = R3 / R0.

[0085] Known equation A 2 -4B(C + 1) > 0 and A 2 -4B(D + 1) > 0 hold. Therefore, T 2 + AT / B + (C + 1) / B has real roots r1 and r2, and T 2 + AT / B + (D + 1) / B has real roots r3 and r4. Based on this, Equation (18) can be further deduced as:

[0086]

[0087] Since the resistance value of the platinum resistor is related to the quadratic term of the target temperature T, after performing a second-order Taylor expansion on Equation (3), we can obtain:

[0088]

[0089] In the formula, f(R2) and f(R3) are the coefficients of T, and g(R2) and g(R3) are the coefficients of the square of the target temperature T 2 When R2 and R3 increase, the non-linear relationship between T and U(t) becomes smaller, reducing the influence of f(R2)T and g(R2)T 2 , f(R3)T and g(R3)T 2 on U(t) is the most significant. Since f(R2) and f(R3), g(R2) and g(R3) have consistent mathematical expressions, there is a normalized expression:

[0090]

[0091] In the formula, R is the bridge arm resistance. Taking the platinum resistor PT1000 as an example, A = 3.862314×10 -3 , B = -6.53493×10 -7 , R0 = 1kΩ, Figure 4 shows the value graph of f(R) when R0 ∈ [0, 10kΩ], Figure 5 shows the value graph of g(R) when R0 ∈ [0, 10kΩ].

[0092] As shown by Figure 4 and Figure 5 , f(R) and g(R) show a trend of "increasing first and then decreasing" as the value of R increases. Further, by taking the derivatives of f(R) and g(R), we can obtain:

[0093]

[0094] Based on this, the extreme point of Equation (22) is:

[0095]

[0096] Since f(R) is the coefficient of T, g(R) is T 2 The coefficient of g(R) has a significantly greater impact on U(t) than f(R). The premise of suppressing output nonlinearity is that g(R) takes the maximum value first, that is, R>>0.516R0. Considering that Equation (23) takes the maximum value, R≥R0. To illustrate the effect of suppressing output nonlinearity, the temperature measurement circuit based on a single-arm bridge is used as an example to simulate the relationship between the target temperature and U(t) when R2 and R3 are different. Let R2=R3∈[0,10kΩ], R1 and R4 are both PT1000, and the constant voltage source is DC5V. The simulation conditions are as follows:

[0097] Table 1 Simulation conditions

[0098]

[0099] Figure 6 The simulation results of U(t) at different target temperatures between 0℃ and 100℃ are given. Figure 7 Its increment dU(t) is given. When R2 and R3 increase, the nonlinear relationship between U(t) and T is weakened, and the nonlinearity of the temperature measurement circuit output is effectively suppressed. However, excessive resistance of R2 and R3 will cause the sensitivity of the temperature measurement circuit to decrease, thereby increasing the temperature measurement error and reducing accuracy and reliability. Therefore, R2 and R3 are consistent and their resistance values must be greater than or equal to R0, R1 and R4 are platinum resistors and their resistance values are R t Based on this, the optimal strategy for the bridge arm resistance value of the high-sensitivity and wide-temperature-range temperature measurement circuit of the present invention is obtained.

[0100] Specific embodiment three: This embodiment differs from specific embodiment one or two in that the value of the resistor R4 is calculated based on the sampling result of the analog-to-digital converter, specifically:

[0101]

[0102] Wherein, U(t) represents the output of the differential amplifier, α represents the amplification factor of the differential amplifier, and U represents the instantaneous output of the constant voltage source.

[0103] Other steps and parameters are the same as those in the first or second embodiment.

[0104] From formula (2), we can see that U(t) is also closely related to the constant voltage source excitation voltage U. If U fluctuates, U(t) will also produce measurement fluctuations. The greater the U fluctuation, the greater the U(t) fluctuation, and the more significant the effect of the excitation error on the temperature measurement accuracy. When the constant voltage source outputs time t DC and the target temperature sampling time t s When asynchronous, the instantaneous value of the constant voltage source output voltage U DC and the target temperature sampling value U SThey are asynchronous sampling values, both of which contain asynchronous measurement errors caused by the output voltage fluctuation of the constant voltage source. When the target temperature is 20 °C, the instantaneous resistance value of PT1000 can be obtained from Equation (17) as follows:

[0105] R4 = R0(1 + AT + BT 2 ) = 1076.985 Ω (25)

[0106] Under the excitation of a constant voltage source of DC 5V, U(t) can be expressed as:

[0107]

[0108] If the output of the constant voltage source is accompanied by an accuracy error of ±1%, and the output of the precision temperature measurement circuit at this time is U″(t), then the asynchronous measurement error ΔU(t) of the temperature measurement circuit is ΔU(t) = |U′(t) - U″(t)|. Figure 8 The asynchronous measurement error ΔU(t) is given under the excitation of a constant voltage source output with an accuracy error of ±1%.

[0109] As shown by Figure 8 , under the excitation of a constant voltage source with an accuracy error of ±1%, U(t) is a fluctuating output and the maximum error value is approximately ±5×10 -4 V. In precision temperature measurement, the asynchronous measurement error ΔU(t) is sufficient to affect the accuracy of precision temperature measurement. In order to effectively eliminate the asynchronous measurement error ΔU(t), the measurement interval Δt between the output U(t) of the precision temperature measurement circuit and the constant voltage source U should be shortened as much as possible. The smaller Δt is, the smaller the asynchronous measurement error ΔU(t) is, and the smaller its impact on the temperature measurement accuracy is. Ideally, it is necessary to make Δt = 0, that is, to synchronously measure U(t) and U, which requires using an analog-to-digital conversion module with synchronous sampling and holding functions for signal sampling.

[0110] As shown by Figure 3 , the lower limit of the temperature measurement range of the single-arm bridge is determined by R3. The smaller R3 is, the lower the lower limit of the temperature measurement range is. To reduce the non-linearity of the single-arm bridge output, let R2 = R3 ≥ R0, and a fixed-value resistor with a precision of 1‰ and a resistance value of 1 kΩ is selected to form R2 = R3 = 1 kΩ. Based on this, PT1000 is used as the temperature measurement sensor. Taking the target temperature of 25 °C as a reference, when the target temperature changes by 0.001 °C, the change amount of the PT1000 resistance value is as follows:

[0111] ΔR4 = R t (25.001) - R t (25) = 3.8296×10 -3 Ω (27)

[0112] To eliminate the asynchronous measurement error, the 18-bit synchronous sampling analog-to-digital converter AD7608 with 8 inputs is selected. It has synchronous sampling and holding functions and can synchronously monitor the output of the precision temperature measurement circuit and the constant voltage source output. DC =4.096V constant voltage source ADR444B excites the precision temperature measurement circuit; ADR421 is selected as the reference source of AD7608, and its output voltage of 2.5V is converted into a 4.5V reference voltage by the internal circuit of AD7608. Based on this, AD7608 resolution U res As shown below:

[0113]

[0114] When the target temperature changes by 0.001°C, the output change ΔU(t) of the precision temperature measurement circuit can be expressed as follows:

[0115] ΔU(t)=7.1401×10 -6 V (29)

[0116] To ensure that the AD7608 can accurately distinguish 0.001°C temperature changes, the output of the precision temperature measurement circuit needs to be amplified by the following multiple α:

[0117]

[0118] Based on this, a differential circuit based on INA118 is designed to collect the output of the precision temperature measurement circuit and input it into AD7608 for analog-to-digital conversion. After conditioning by INA118, the output of the precision temperature measurement circuit is as follows:

[0119]

[0120] In the formula, 50K represents the high-precision resistor built into INA118, and R5 represents the external high-precision bypass resistor. Therefore, R5 can be expressed as:

[0121]

[0122] A fixed resistor with an accuracy of 1‰ and a resistance of 10kΩ is selected to form R5 = 10kΩ. At this time, the amplification factor α = 6. After conditioning by the INA118, when the output of the precision temperature measurement circuit is the full-scale input value of the AD7608, the target temperature at this time is the upper limit of the temperature measurement range. Knowing that the reference voltage of the AD7608 is 4.5V, it can be obtained from formula (13):

[0123]

[0124] After the equation in formula (1) is solved, the upper limit of the temperature measurement range is 118.443 °C, that is, the temperature measurement range is 0 °C to 118.443 °C. This indicates that the temperature measurement range of the precision temperature measurement circuit of the present invention spans approximately 118 °C. By adjusting R3, the lower limit of the temperature measurement range can be adjusted, thereby achieving the goal of adjusting the temperature measurement range.

[0125] Specific Embodiment 4. The difference between this embodiment and one of Embodiments 1 to 3 is that the working process of the resistance processing module is as follows:

[0126] Step 1, moving average filtering

[0127]

[0128] Among them, R 4,i represents the sensed resistance value calculated according to the acquisition result at the i-th sampling point, M represents the adaptive window width, represents the sensed resistance value at the m-th sampling point obtained after moving average filtering processing;

[0129] Step 2, the main thread performs second-order Butterworth low-pass filtering

[0130]

[0131] Among them, represents the sensed resistance value at the m-th sampling point obtained after second-order Butterworth low-pass filtering processing;

[0132] Step 3, set the frequency of the system timer triggering an interrupt to f c , when the system timer triggers an interrupt, the auxiliary thread outputs the sensed resistance value after second-order Butterworth low-pass filtering at the moment of triggering the interrupt. When the system timer does not trigger an interrupt, the auxiliary thread directly outputs the sensed resistance value after second-order Butterworth low-pass filtering obtained at the previous moment of triggering the interrupt. The temperature calculation module subsequently performs temperature calculation based on the sensed resistance value output by the auxiliary thread.

[0133] Using a dual-running thread interactive digital filter can accurately filter out the random error of the sampling value of a high-sensitivity wide-temperature measurement range temperature measurement circuit. The purpose of the main thread running the second-order Butterworth low-pass filter is to improve the accuracy of the temperature measurement value. The auxiliary thread interacts with the main thread to filter the temperature measurement value. Compared with the existing method, in the present invention, only when the system timer triggers an interrupt will it affect the running process of the main thread, and at other times the running process of the main thread will not be affected, which can ensure the running efficiency of the main thread, and thus ensure the rapid convergence and real-time output of the temperature measurement value.

[0134] Other steps and parameters are the same as those in any one of the first to third specific embodiments.

[0135] After being converted by the AD7608, an Adaptive WindowWidth MovingAverage Filter (AWW moving average filter) with a window width of M performs a moving average filtering operation on the temperature measurement sampling values according to the sampling frequency f S (unit: Hz). When the temperature measurement sampling values do not fill the AWW moving average filter, the rough value of the temperature measurement sampling value is obtained by summing and averaging according to the actual number m of the filled temperature measurement sampling values; when the temperature measurement sampling values fill and overflow the AWW moving average filter, the rough value of the temperature measurement sampling value is obtained by summing and averaging according to the width M.

[0136] The window width of the AWW moving average filter is dynamically adjusted by the sampling frequency f S , and the higher the sampling frequency f S , the larger the window width, and the better the effect of filtering out the accidental error of the sampling value. Considering that the temperature is a large inertia link, the number of sampling values at 3 times the sampling frequency f S is used as the window width of the AWW moving average filter. Therefore, when the temperature measurement sampling values fill and overflow the AWW moving average filter, the expression of the AWW moving average filter is as follows:

[0137]

[0138] Considering that the temperature is a large inertia link, when the sampling frequency is f S = 20Hz, it can basically meet the requirements of precise temperature measurement under normal circumstances. Then the expression of the AWW moving average filter is as follows:

[0139]

[0140] Design a fast convergence method for temperature measurement data based on a dual-running thread interactive digital filter to accurately filter out the random error of the sampling values of a temperature measurement circuit with high sensitivity and a wide temperature measurement range. The fast convergence method for temperature measurement data based on a dual-running thread interactive digital filter consists of a main thread and a secondary thread. The main thread runs a second-order Butterworth low-pass filter according to the sampling frequency f S to filter the rough value of the temperature measurement sampling value in real time and improve the accuracy of the temperature measurement value; the secondary thread interacts with the main thread to filter the temperature measurement value according to the temperature measurement frequency f c (unit: Hz and f C ≤ f S ) to ensure the fast convergence and real-time output of the temperature measurement value.

[0141] The noise of the temperature measurement circuit increases the randomness of the temperature measurement value, and the inherent deviation of the temperature measurement circuit causes the measured temperature value to deviate from the theoretical value. A second-order Butterworth low-pass filter is designed to filter out the high-frequency noise of the rough value of the temperature measurement sampling value, and the output of the main thread is obtained. The passband gain α P of the second-order Butterworth low-pass filter is 3 dB, the stopband attenuation α S is 40 dB, and the cut-off frequency F P is 0.02, and its expression is shown in Equation (36).

[0142] The secondary thread interacts with the main thread to filter the temperature measurement value according to the temperature measurement frequency f c (in Hz and f C ≤f S ). The frequency at which it takes values from the second-order Butterworth low-pass filter of the main thread is triggered by the system timer Timer, that is, the interrupt frequency of the system timer Timer is set to f c . When the system timer Timer triggers an interrupt, the secondary thread directly obtains the filtered temperature measurement value from the output of the main thread at the current sampling moment t(N) as the current temperature measurement value; when the system timer Timer does not trigger an interrupt, the output of the secondary thread is the filtered temperature measurement value obtained from the output of the main thread at the previous sampling moment t(N - 1) as the current temperature measurement value, so as to ensure the rapid convergence and real-time output of the temperature measurement value.

[0143] Using an adaptive window width moving average filter can effectively filter out the accidental errors of the sampling values of the temperature measurement circuit with high sensitivity and wide temperature measurement range, ensuring the consistency, repeatability and regularity of the sampling results; using a dual-running thread interactive digital filter can accurately filter out the random errors of the sampling values of the temperature measurement circuit with high sensitivity and wide temperature measurement range. The main thread runs a second-order Butterworth low-pass filter to improve the accuracy of the temperature measurement value. The secondary thread interacts with the main thread to filter the temperature measurement value, which can ensure the rapid convergence and real-time output of the temperature measurement value.

[0144] Specific implementation mode 5. The difference between this implementation mode and one of the specific implementation modes 1 to 4 is that the temperature calculation module is used to calculate the target temperature T′ according to the processed resistance R4 value, specifically:

[0145]

[0146] In the formula, A, B, and R0 are platinum resistance parameters.

[0147] Other steps and parameters are the same as those in one of the specific implementation modes 1 to 4.

[0148] Use a high-precision, low-temperature-drift fixed-value resistor R = 1140.25 Ω (corresponding temperature is 36.0775 °C) for a 30-minute accuracy testFigure 9 The temperature measurement data filtering effect diagram is given.

[0149] As Figure 9 shown, the digital filter filters out noise well. The actual temperature measurement error is less than ±0.001 °C, and as the working time increases, the data smoothing effect of the filter becomes more obvious. In view of the non-linearity of the platinum resistance PT1000, the "temperature-resistance" calculation equation is designed by Equation (8) to calculate the target temperature in real time, and its expression is as shown in Equation (38). In the formula, A = 3.8623139728×10 -3 , B = -6.534932626×10 -7 , R0 = 1000 Ω. Substituting the finally obtained sensed resistance value into Equation (38), the target temperature at each moment can be calculated.

[0150] Specific implementation manner six: The difference between this implementation manner and one of the first to fifth specific implementation manners is that the working process of the temperature correction module is as follows:

[0151] T″ = f LSM2 (T′) = -0.0012T′ 2 +1.1634T′ - 0.7834 (39)

[0152] where T″ represents the corrected temperature.

[0153] Other steps and parameters are the same as those in one of the first to fifth specific implementation manners.

[0154] By selecting low-temperature drift and 1‰ accuracy 10 KΩ and 1 KΩ fixed-value resistors in the range of 0 °C to 118 °C and constructing multi-point target temperature tests in a series-parallel manner, and using the measured value T′ and the theoretical value T″ to construct the temperature correction model of Equation (39) based on the least squares method. The temperature measurement value correction method based on the least squares can accurately correct the temperature measured value according to the theoretical value of the temperature measurement value.

[0155] Specific implementation manner seven: The difference between this implementation manner and one of the first to sixth specific implementation manners is that the temperature measurement system further includes a data storage module, and the data storage module is used to store each group of resistance values and temperature values calculated during the temperature measurement process;

[0156] The capacity N of the data storage module is:

[0157] N = f c t c (40)

[0158] where f c represents the temperature measurement frequency, and t c represents the cache time.

[0159] Other steps and parameters are the same as those in any one of the first to sixth specific embodiments.

[0160] The data storage module is a circular storage area. When the cached data exceeds the number of entries that the circular storage area can accommodate, an overwrite operation needs to be performed, starting from the head of the circular buffer, so as to achieve the purpose of saving storage space. The temperature measurement data is transmitted to the remote end in real time, and the local display of the temperature measurement data can be realized through the OLED.

[0161] Experimental verification

[0162] To verify the temperature measurement accuracy of the method of the present invention, within the temperature measurement range of 0°C to 118°C, the resistance values of 10.014°C (corresponding resistance value of 1038.61Ω), 52.244°C (corresponding resistance value of 1200Ω), and 87.603°C (corresponding resistance value of 1333.33Ω) are arbitrarily selected as the target temperature reference values to replace R1 and R4 of the precision temperature measurement system, and three 10-minute tests are carried out at the target temperature reference values. Figure 10 The temperature measurement curve at 10.014°C is given, Figure 11 The temperature measurement curve at 52.244°C is given, Figure 12 The temperature measurement curve at 87.603°C is given.

[0163] As shown by Figure 10 , Figure 11 , Figure 12 , the high-frequency noise is effectively suppressed, the temperature measurement value fluctuates around the target temperature reference value, and the temperature measurement accuracy is better than ±0.001°C; as the test time increases, the envelope effect of the temperature measurement value around the target temperature reference value becomes more significant. This shows that the temperature measurement method of the present invention can effectively improve the accuracy and reliability of precision temperature measurement.

[0164] Specific embodiment eight: A temperature measurement method based on an optimized single-arm bridge and interactive digital filtering described in this embodiment, the method specifically includes the following steps:

[0165] Step 1: Use the resistor R4 in the second measurement arm of the single-arm bridge as a temperature sensor to sense the target temperature;

[0166] Step 2: Use a constant voltage source DC to excite the single-arm bridge, use the voltage at the reference point on the first measurement arm and the voltage at the reference point on the second measurement arm as the inputs of the differential amplifier, and use an analog-to-digital converter to synchronously sample the voltage of the constant voltage source and the output voltage of the differential amplifier. Denote the sampled output voltage of the differential amplifier as U(t), and denote the sampled voltage of the constant voltage source as U;

[0167] Step 3: Calculate the resistance value of R4 using the sampled U(t) and U, after processing the calculated resistance value, then calculate the target temperature T′ based on the processed resistance;

[0168] Step Four: Calibrate the target temperature T′ calculated in Step Three to obtain the final target temperature detection result.

[0169] Specific Embodiment Nine: The difference between this embodiment and Specific Embodiment Eight is that the specific process of Step Three is as follows:

[0170] Step 3-1: Calculate the resistance value R using U(t) and U sampled at the m-th sampling point 4,m :

[0171]

[0172] where U(t) represents the output of the differential amplifier, α represents the amplification factor of the differential amplifier circuit, U represents the instantaneous output of the constant voltage source, and R 4,m represents the sensed resistance value at the m-th sampling point;

[0173] Step 3-2: Perform moving average filtering

[0174]

[0175] where R 4,i represents the sensed resistance value calculated based on the acquisition result at the i-th sampling point, M represents the adaptive window width, represents the sensed resistance value at the m-th sampling point obtained after moving average filtering;

[0176] Step 3-3: The main thread performs second-order Butterworth low-pass filtering

[0177]

[0178] where represents the sensed resistance value at the m-th sampling point obtained after second-order Butterworth low-pass filtering;

[0179] Step 3-4: Set the frequency of the system timer to trigger an interrupt as f c , when the system timer triggers an interrupt, the secondary thread outputs the sensed resistance value after second-order Butterworth low-pass filtering at the moment of interrupt trigger. When the system timer does not trigger an interrupt, the secondary thread directly outputs the sensed resistance value after second-order Butterworth low-pass filtering obtained at the previous interrupt trigger moment;

[0180] Step 3-5: Calculate the temperature based on the sensed resistance value output by the secondary thread:

[0181]

[0182] where T′ represents the calculated temperature.

[0183] The other steps and parameters are the same as those in the eighth specific implementation manner.

[0184] Tenth specific implementation manner: The difference between this implementation manner and the eighth or ninth specific implementation manner is that the specific process of step 4 is as follows:

[0185] T″ = f LSM2 (T′) = -0.0012T′ 2 +1.1634T′ - 0.7834 (45)

[0186] Where T″ represents the corrected temperature.

[0187] The other steps and parameters are the same as those in the eighth or ninth specific implementation manner.

[0188] The above examples of the present invention are only for explaining in detail the calculation model and calculation process of the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A temperature measurement system based on an optimized single-arm bridge and interactive digital filtering, characterized in that, The system includes a single-arm bridge, a differential amplifier, an analog-to-digital converter, a resistance calculation module, a resistance processing module, a temperature calculation module, and a temperature correction module; wherein: The single-arm bridge includes a constant voltage source, a first measurement arm, and a second measurement arm. The first measurement arm includes resistors R1 and R3, and the second measurement arm includes resistors R2 and R4. The resistor R4 in the single-arm bridge serves as the sensing resistor for the target temperature. The voltages at the reference points of the first measurement arm and the second measurement arm are input into the differential amplifier. The analog-to-digital converter is used to synchronously collect the voltage of the constant voltage source and the output voltage of the differential amplifier. The resistance calculation module is used to calculate the value of resistor R4 based on the sampling results of the analog-to-digital converter. The resistance processing module is used to process the value of resistor R4, and the temperature calculation module is used to calculate the target temperature T′ based on the processed value of resistor R4. The temperature correction module is used to correct the calculated target temperature T′ to obtain the corrected target temperature, that is, to obtain the temperature detection result.

2. The temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 1, wherein The resistors R1 and R4 are both platinum resistors PT1000; R2 = R3 = R0, where R0 represents the resistance value of the platinum resistor PT1000 when the target temperature is 0°C.

3. A temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 1, characterized in that, The calculation of the value of resistor R4 based on the sampling results of the analog-to-digital converter is specifically as follows: Where U(t) represents the output of the differential amplifier, α represents the amplification factor of the differential amplifier, and U represents the instantaneous output of the constant voltage source.

4. The temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 1, characterized in that, The working process of the resistance processing module is as follows: Step 1, moving average filtering Among them, R 4,i represents the sensed resistance value calculated based on the acquisition result at the i-th sampling point, M represents the adaptive window width, represents the sensed resistance value at the m-th sampling point obtained through moving average filtering; Step 2, the main thread performs second-order Butterworth low-pass filtering Among them, represents the sensed resistance value at the m-th sampling point obtained through second-order Butterworth low-pass filtering processing; Step 3: Set the frequency of the system timer triggering an interrupt to f c , when the system timer triggers an interrupt, the secondary thread outputs the sensed resistance value after second-order Butterworth low-pass filtering at the moment of interrupt triggering. When the system timer does not trigger an interrupt, the secondary thread directly outputs the sensed resistance value after second-order Butterworth low-pass filtering obtained at the previous interrupt triggering moment.

5. A temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 1, characterized in that, The temperature calculation module is used to calculate the target temperature T′ based on the processed value of resistor R4, specifically as follows: In the formula, A, B, and R0 are platinum resistor parameters.

6. The temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 5, wherein, The working process of the temperature correction module is as follows: T″ = f LSM2 (T′) = -0.0012T′ 2 +1.1634T′ - 0.7834 (39) Where T″ represents the corrected temperature.

7. A temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 1, characterized in that, The temperature measurement system further includes a data storage module, which is used to store the groups of resistance values and temperature values calculated during the temperature measurement process. The capacity N of the data storage module is: N = f c t c (40) Among them, f c represents the temperature measurement frequency, and t c represents the cache time.

8. The temperature measurement method of a temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 1, characterized in that, The method specifically includes the following steps: Step 1, use the resistor R4 in the second measurement arm of the single-arm bridge as a temperature sensor to sense the target temperature. Step 2, use the constant voltage source DC to excite the single-arm bridge, use the voltages at the reference points of the first measurement arm and the second measurement arm as the inputs of the differential amplifier, and use the analog-to-digital converter to synchronously sample the voltage of the constant voltage source and the output voltage of the differential amplifier. Denote the sampled output voltage of the differential amplifier as U(t), and denote the sampled voltage of the constant voltage source as U. Step 3, calculate the resistance value of R4 using the sampled U(t) and U, process the calculated resistance value, and then calculate the target temperature T′ based on the processed resistance. Step 4, correct the target temperature T′ calculated in Step 3 to obtain the final target temperature detection result.

9. The temperature measurement method of a temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 8, characterized in that, The specific process of Step 3 is as follows: Step 3-1: Calculate the resistance value R using U(t) and U sampled at the m-th sampling point 4,m : Among them, U(t) represents the output of the differential amplifier, α represents the amplification factor of the differential amplification circuit, U represents the instantaneous output of the constant voltage source, and R 4,m represents the sensed resistance value at the m-th sampling point; Step 3-2, moving average filtering wherein, R 4,i represents the sensed resistance value calculated according to the acquisition result at the i-th sampling point, M represents the adaptive window width, represents the sensed resistance value at the m-th sampling point obtained through moving average filtering; Step 3-3, the main thread performs second-order Butterworth low-pass filtering Among them, represents the sensed resistance value at the m-th sampling point obtained through second-order Butterworth low-pass filtering. Step 3 and 4: Set the frequency at which the system timer triggers an interruption to f c . When the system timer triggers an interruption, the secondary thread outputs the sensed resistance value after second-order Butterworth low-pass filtering at the moment of the triggered interruption. When the system timer does not trigger an interruption, the secondary thread directly outputs the sensed resistance value after second-order Butterworth low-pass filtering obtained at the moment of the previous triggered interruption; Step 3-5, perform temperature calculation according to the sensed resistance value output by the auxiliary thread: Where T′ represents the calculated temperature.

10. A temperature measurement method for a temperature measurement system based on an optimized single-arm bridge and interactive digital filtering according to claim 9, characterized in that, The specific process of the fourth step is as follows: T″ = f LSM2 (T′) = -0.0012T′ 2 +1.1634T′ - 0.7834 (45) Where T″ represents the corrected temperature.

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