A platinum resistance high-precision temperature measuring device and method capable of automatically identifying wiring modes

Abstract

The application discloses a kind of platinum resistance high-precision temperature measuring device of automatic identification wiring mode, including power module, signal detection module, isolation module, signal processing module and cold end temperature measurement module.Power module is powered for signal detection and processing module, signal detection module contains sensing probe, wiring identification circuit, constant current source, measurement circuit and analog-digital conversion circuit.Sensing probe measures the temperature to be measured, wiring identification circuit automatically determines two, three or four-wire system and feedback result, constant current source provides positive and negative constant current excitation, measurement circuit acquires and processes feedback voltage and then sends into analog-digital conversion circuit.Analog-digital conversion circuit is connected with signal processing module through isolation module, signal processing module calls corresponding algorithm according to wiring identification result, and outputs final temperature data.The application can realize ±0.02 ℃ level high-precision temperature measurement in the range of-200 ℃ to 850 ℃ under three / four-wire system and low-speed sampling conditions.

Description

Technical Field

[0001] This invention belongs to the field of temperature measurement technology, and in particular relates to a high-precision platinum resistance temperature measuring device and method that automatically identifies the wiring method. Background Technology

[0002] Existing platinum resistance thermometer (PTT) temperature measurement systems typically employ an integrated analog-to-digital converter (ADC) with a built-in excitation current source combined with lookup tables or second-order linearization algorithms, which has significant limitations. For example, patent CN1111141406B proposes a PT100 temperature measurement system that improves robustness through parallel connection of multiple sensors and electrical isolation, but the excitation current source error is still relatively large (above ±1%), resulting in self-heating errors often exceeding ±0.1°C, failing to meet the ±0.02°C accuracy requirement. Furthermore, this patent does not accurately compensate for cold junction errors introduced by changes in wire and ambient temperature, especially at extreme temperatures where circuit component drift amplifies measurement deviations. In addition, the multi-wire wiring method relies on manual configuration and cannot be automatically identified, leading to cumbersome and error-prone field deployment. The lack of online self-calibration mechanisms and digital isolation communication functions hinders long-distance industrial deployment and remote maintenance. These bottlenecks limit the system's application in precision instruments and complex environments, making it difficult to achieve stable, high-precision temperature measurement over a wide temperature range (-200°C to 850°C). Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-precision platinum resistance temperature measuring device and method for automatically identifying wiring methods, so as to achieve high-precision temperature measurement over a wide temperature range.

[0004] To achieve the above-mentioned objectives, this invention provides a high-precision platinum resistance temperature measuring device with automatic identification of wiring methods, comprising a power supply module, a signal detection module, an isolation module, and a signal processing module. The power supply module supplies power to the signal detection module and the signal processing module. The signal detection module is connected to the signal processing module through the isolation module. The signal detection module includes a sensing probe, a wiring adaptive identification circuit, a constant current source circuit, a measurement circuit, and an analog-to-digital conversion circuit. The sensing probe measures the temperature of the object under test and transmits the data to the measurement circuit. The wiring adaptive identification circuit is connected between the sensing probe and the measurement circuit to automatically identify the current wiring method and feed it back to the signal processing module. The constant current source circuit outputs a constant current signal and excites the sensing probe through the measurement circuit. The measurement circuit collects the voltage signal fed back by the sensing probe, processes it, and outputs it to the analog-to-digital conversion circuit for digital conversion. The analog-to-digital conversion circuit transmits the converted digital signal to the signal processing module through the isolation module. The signal processing module calls the corresponding temperature calculation program to analyze the signal fed back by the measurement circuit and convert it into temperature data based on the wiring identification result fed back by the wiring adaptive identification circuit.

[0005] Preferably, the constant current source circuit adopts a modified Howland constant current source structure, with its input terminal connected to the digital-to-analog converter circuit and the power supply module. This circuit, constructed through an operational amplifier, an RC feedback network, and a current sampling branch, can stably output a constant current under bidirectional drive to excite the platinum resistance sensing probe. This structure ensures the accuracy and stability of the output current while reducing the impact of temperature drift and circuit noise, thereby improving the accuracy and reliability of the entire temperature measurement system.

[0006] Preferably, the digital-to-analog conversion circuit uses an AD5761 DAC chip and its peripheral circuitry.

[0007] Preferably, the sensing probe is a platinum resistance thermometer (RTD) with a model number of PT100, PT500, or PT1000.

[0008] Preferably, the wiring adaptive identification circuit includes a multiplexer, a voltage sampling unit, and a controllable switch module.

[0009] The multiplexer has multiple inputs connected to different pins of the platinum resistance thermometer probe, and different wiring combinations can be selected by switching control signals. Its output is connected to the voltage sampling unit, which transmits the level signal from the probe port to the analog-to-digital converter circuit. The voltage sampling unit is connected to a power supply and a filter circuit to stabilize the sampling signal. The controllable switch module is made of semiconductor devices and can dynamically connect or disconnect specific nodes under the control of the signal processing module, thereby realizing automatic identification of two-wire, three-wire, or four-wire wiring methods.

[0010] Preferably, the measurement circuit includes a differential amplifier circuit, a low-pass filter circuit, and a bias circuit connected in sequence. The measurement circuit inputs the voltage signal fed back by the sensing probe into the analog-to-digital converter circuit after differential amplification, filtering, and biasing.

[0011] Preferably, the measurement circuit includes multiple platinum resistance interfaces, a controllable analog switch, a reference resistor, and an amplification and filtering unit.

[0012] The circuit comprises a platinum resistance interface for connecting to different pins of the sensor probe; an analog switch dynamically configures the measurement circuit under the control of the signal processing module to adapt to two-wire, three-wire, or four-wire wiring methods; a reference resistor and the platinum resistance resistor together form a measurement bridge circuit and serve as the reference input for the analog-to-digital converter (ADC); an amplification unit differentially amplifies the sensor voltage difference; a filtering unit employs a multi-stage low-pass structure to suppress high-frequency noise; and a bias unit introduces a stable DC reference voltage to adjust the signal to the input range of the ADC circuit. This measurement circuit maintains high-precision voltage acquisition and anti-interference performance under different wiring methods, ensuring the accuracy of subsequent temperature calculations.

[0013] Preferably, the analog switch one, analog switch two, analog switch three, and analog switch four are all dual-channel analog switches, model TS3A5233.

[0014] Preferably, the analog-to-digital converter circuit uses an AD7175-2, with its pins AIN0 and AIN1 respectively connected to a reference resistor R. ref The first and second terminals are connected, pin AIN2 is connected to the output terminal of the measurement circuit, and pins GPIO0 and GPIO1 are connected to the wiring adaptive identification circuit.

[0015] Preferably, the isolation module includes an SPI isolation circuit, one side of which is connected to an analog-to-digital converter circuit and the other side is connected to a signal processing module, for achieving electrical isolation between the analog-to-digital converter circuit and the signal processing module. The SPI isolation circuit uses an ADuM1401 chip and its peripheral circuits.

[0016] Preferably, the isolation module further includes an I²C isolation circuit. One side of the I²C isolation circuit is connected to the signal processing module, and the other side is connected to a cold junction temperature measurement module. The cold junction temperature measurement module is used to measure the cold junction temperature data of the circuit in real time and feed it back to the signal processing module. The I²C isolation circuit uses an ADuM1250 chip and its peripheral circuits.

[0017] Preferably, the cold junction temperature measurement module is a digital temperature sensor TMP117 or TMP119.

[0018] Preferably, the signal processing module is connected to a server / host computer via a data cable or wireless network, and the signal processing module is a microcontroller, model STM32F407VET6.

[0019] The present invention also provides a temperature measurement method, which is based on the above-mentioned adaptive wide-range platinum resistance high-precision temperature measuring device, and includes the following steps:

[0020] Step 1: After the system is powered on, it performs a self-test and automatically determines the wiring method of the sensor probe through the wiring identification circuit;

[0021] Step 2: Based on the recognition results output by the signal processing module, configure the analog switch to form the corresponding measurement circuit;

[0022] Step 3: Sample the platinum resistance multiple times with both forward and reverse constant current, record the multi-channel voltage data, and eliminate system offset by differential or averaging methods to obtain the resistance measurement value of the platinum resistance; at the same time, the cold junction temperature measurement module collects the ambient temperature data around the device in real time as a compensation reference.

[0023] Step 4: The signal processing module performs linearization calculations on the resistance measurement value to obtain the initial temperature value, and then corrects it by combining the cold junction temperature data and the preset compensation model, outputting the final measured temperature result.

[0024] Preferably, the wiring identification process includes: when the system enters wiring detection, the control signal output by the analog-to-digital converter circuit controls the opening and closing of the corresponding switch by the wiring adaptive identification circuit to obtain the calibration voltage, the first wiring voltage, the second wiring voltage and the third wiring voltage. The calibration voltage is used as a reference. The first wiring voltage to the third wiring voltage correspond to the measurement results of different wiring terminal combinations. Through threshold comparison and logical judgment, the two-wire, three-wire or four-wire system is automatically inferred.

[0025] Preferably, step three further includes measuring the cold junction temperature, using a cold junction temperature measurement module to collect the circuit board temperature in real time and feed it back to the signal processing module; step four involves the signal processing module combining the resistance value R... meas The temperature data is obtained by calculating the cold end temperature data and the compensation model, the linearization formula and the compensation formula. The compensation model is obtained by collecting error data at different plate temperatures through a constant temperature bath calibration experiment before temperature measurement and fitting the data.

[0026] Compared with existing technologies, the advantages of this invention are: achieving high-precision temperature measurement of ±0.02°C, significantly better than the ±0.1°C to ±0.2°C error of traditional systems; adaptive wiring identification simplifies field installation, supports various platinum resistance thermometers such as PT100, PT500, and PT1000, and reduces the risk of configuration errors; cold junction compensation significantly reduces errors, making it suitable for wide temperature range applications; digital isolation and remote communication enhance the anti-interference capability and system integration in industrial settings; and the system supports online self-calibration and remote upgrades, reducing maintenance costs and improving equipment reliability and lifespan. Attached Figure Description

[0027] Figure 1 This is a system block diagram of a platinum resistance high-precision temperature measuring device that automatically identifies the wiring method, according to an example of the present invention.

[0028] Figure 2 This is an improved Howland constant current source circuit diagram of an example of the present invention.

[0029] Figure 3 This is a circuit diagram of the wiring adaptive identification circuit of an example of the present invention.

[0030] Figure 4 This is a schematic diagram of a measurement circuit according to an example of the present invention.

[0031] Figure 5 This is a circuit diagram of the analog-to-digital conversion circuit of an example of the present invention.

[0032] Figure 6 This is a wiring diagram of the isolation circuit in an example of the present invention.

[0033] Figure 7 This is a flowchart of the temperature measurement method in an example of the present invention.

[0034] Figure 8 This is a flowchart of the online calibration process for the cold junction compensation coefficient in an example of the present invention.

[0035] Figure 9 This is the final temperature calculation flowchart of an example of the present invention.

[0036] In the diagram, 1 is the power supply module; 2 is the signal detection module; 3 is the isolation module; 4 is the signal processing module; 5 is the cold junction temperature measurement module; and 6 is the server / host computer. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0038] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0040] To make the description of this disclosure more detailed and complete, the following is an illustrative description of the embodiments and specific examples of the present invention; however, this is not the only form of implementing or using the specific examples of the present invention. The embodiments cover the characteristics of multiple specific examples, as well as the methods, steps, and their order for constructing and operating these specific examples. However, other specific examples can also be used to achieve the same or equivalent functions and step sequences.

[0041] This invention enables high-precision temperature measurement of various platinum resistance thermometers. To facilitate the explanation of the specific temperature measurement measures, the following embodiments use the PT1000 as an example for detailed description. As a typical platinum resistance sensor, the PT1000 has a resistance of 1000Ω at 0°C, conforms to the IEC60751 standard, possesses excellent linearity and long-term stability, and is suitable for a wide temperature range from -200°C to 850°C. It is widely used in industrial process control and environmental monitoring.

[0042] The symbol naming rules described in the following examples are as follows. For operational amplifiers (such as OP1A, OP2, etc.), the voltage at the non-inverting input terminal is represented by "V". OP[X]+ " indicates that [X] is the op-amp number, for example, "V OP1A+ "Indicates the positive input voltage of OP1A. The inverting input voltage is represented by "V". OP[X]- "Indicates, for example, "V" OP1A- "Indicates the inverted input voltage of OP1A. The output voltage is expressed in "V". OP[X]O "Indicates, for example, "V" OP1AO " indicates the output voltage of OP1A. Other op-amps are similar; for example, op-amp OP2 is represented by "V". OP2+ "、"V OP2- "and"V OP2O ".

[0043] Example 1:

[0044] like Figure 1As shown, this invention provides a high-precision platinum resistance temperature measuring device with automatic identification of wiring methods, including a power supply module 1, a signal detection module 2, an isolation module 3, and a signal processing module 4. The power supply module 1 supplies power to the signal detection module 2 and the signal processing module 4, and the signal detection module 2 is connected to the signal processing module 4 through the isolation module 3. The signal detection module 2 includes a sensing probe, a wiring adaptive identification circuit, a constant current source circuit, a measurement circuit, and an analog-to-digital conversion circuit. The power supply module 1 outputs ±5V to provide reference voltage for the various precision operational amplifiers, analog-to-digital conversion circuits, and digital-to-analog conversion circuits in the circuit, and simultaneously converts +3.3V to power the microcontroller (MCU), ensuring stable operation of all parts of the system.

[0045] In this embodiment, the sensing probe is a PT1000 platinum resistance RTD. In other embodiments of the present invention, the model can also be PT100, PT500, etc. The sensing probe is used to measure the temperature of the object under test and transmit it to the measurement circuit. The wiring adaptive identification circuit is connected between the sensing probe and the measurement circuit to automatically identify the current wiring method and feed it back to the signal processing module 4. The constant current source circuit is used to output a constant current signal and excite the sensing probe through the measurement circuit. The measurement circuit collects the voltage signal fed back by the sensing probe, processes it, and outputs it to the analog-to-digital conversion circuit for digital conversion. The analog-to-digital conversion circuit transmits the converted digital signal to the signal processing module 4 through the isolation module 3. The signal processing module 4 calls the corresponding temperature calculation program to analyze the signal fed back by the measurement circuit and convert it into temperature data based on the wiring identification result fed back by the wiring adaptive identification circuit.

[0046] Specifically, such as Figure 2 As shown, the constant current source circuit in this embodiment is a modified Howland constant current source, whose input terminal is connected to power module 1 through a digital-to-analog converter circuit; the constant current source circuit includes operational amplifier OP1A, operational amplifier OP1B, resistors R1, R2, R3, R4, R5, and R... load Capacitors C1 and C2; the first end of resistor R1 is grounded, and the second end is connected to the first end of resistor R3, the first end of capacitor C1, and the inverting input of operational amplifier OP1A; the second end of resistor R3, the second end of capacitor C1, and the output of operational amplifier OP1A are all connected to the first end of resistor R5; the first end of resistor R2 serves as the input of a constant current source circuit and is connected to the digital-to-analog converter circuit, and the second end is connected to the non-inverting input of operational amplifier OP1A, the first end of capacitor C2, and the first end of resistor R4; the second end of capacitor C2 is grounded; the second end of resistor R4 is connected to the output of operational amplifier OP1B; the non-inverting input of operational amplifier OP1B is connected to the second end of resistor R5, resistor R... loadThe first terminal is connected, and the inverting input terminal and the output terminal of the operational amplifier OP1B are connected; resistor R load The second terminal is connected to the constant current source circuit output terminal and the measurement circuit.

[0047] This constant current source circuit uses a modified Howland constant current source, consisting of a differential amplifier unit, a feedback network, and filtering components. It can stably output a constant current under positive and negative switching. The output impedance is greater than 100MΩ, effectively reducing self-heating effects and thus ensuring high-precision measurement by the platinum resistance sensor.

[0048] Simultaneously, a digital-to-analog converter circuit generates a precise analog voltage signal, which is then converted into a ±500μA constant current signal using a modified Howland constant current source. The DAC signal at the constant current source input is provided by a low-temperature drift, low-noise, and low-glitch 16-bit bipolar voltage output DAC chip, the AD5761, which can stably output voltages from -5V to +5V and supports positive / negative current switching to eliminate offset errors. Operational amplifiers OP1A and OP1B are both OPA2192 precision operational amplifiers, characterized by low input bias current, low noise, high common-mode rejection ratio, and support for dual power supply and rail-to-rail input / output.

[0049] Based on this constant current source circuit, and according to the principles of "virtual open" and "virtual short" and Kirchhoff's current law, the following relationship can be obtained:

[0050]

[0051] When R1=R2=R3=R4, it can be deduced that the current through resistor R5 is:

[0052]

[0053] It can be seen that the constant current source and U DAC Related to resistor R5, set R5=5K, and U DAC The voltage range is -5V to +5V, therefore the constant current source output range is -1~1mA, and the resistor R... load For the load, the equivalent circuit uses a platinum resistance thermometer (PTD), in this example a PT1000. Based on the thermal effect of the platinum resistance thermometer, the current range provided should be -500 μA to 500 μA to balance accuracy and self-heating effects.

[0054] like Figure 3 As shown, the wiring adaptive identification circuit includes a four-channel multiplexer ADG704, resistors R6 and R7, capacitor C3, and MOSFET Q1.

[0055] In this embodiment, the S1 switch of the four-channel multiplexer ADG704 is connected to the first terminal of the platinum resistance RTD via node T0, the S2 switch is connected to the first terminal of the platinum resistance RTD via node T1, the S3 switch is connected to the second terminal of the platinum resistance RTD via node T3, and the S4 switch is connected to the second terminal of the platinum resistance RTD via node T2. Its common output terminal D is connected to the first terminal of resistor R6, the voltage acquisition terminal of the analog-to-digital converter circuit, and the first terminal of capacitor C3, respectively. Terminals A0 and A1 are connected to the GPIO control terminals of the analog-to-digital converter circuit, respectively. The second terminal of resistor R6 is connected to a +5V power supply; the second terminal of capacitor C3 is grounded; the gate of MOSFET Q1 is connected to the control signal output terminal of signal processing module 4, the source is connected between node T2 and terminal S4, and the drain is grounded via resistor R7. In this embodiment, the MOSFET is preferably an N7002 type field-effect transistor.

[0056] like Figure 4 As shown, the measurement circuit in this example includes a differential amplifier circuit, a low-pass filter circuit, and a bias circuit connected in sequence. The measurement circuit inputs the voltage signal fed back by the sensor probe into the analog-to-digital converter circuit after differential amplification, filtering, and biasing.

[0057] Specifically, the measurement circuit includes interfaces 1 to 4 of the platinum resistance RTD, analog switches one to four, and a reference resistor R. ref Resistors R8 to R16, capacitors C4 to C9, operational amplifier OP2, operational amplifier OP3A, and operational amplifier OP3B.

[0058] The wiring methods for each interface of the platinum resistance RTD are as follows: In the two-wire system, the platinum resistance RTD is connected to interface 2 and interface 3; in the three-wire system, the lead on the same side of the platinum resistance RTD is connected to interface 1 and interface 2, and the other end is connected to interface 3; in the four-wire system, the lead on one side of the platinum resistance RTD is connected to interface 1 and interface 2, and the other side is connected to interface 3 and interface 4.

[0059] Interface 1 is simultaneously connected to the reference resistor R via node T0. ref One end and analog switch one; reference resistor R refThe other end is grounded via analog switch three, and its voltage serves as the reference input for the analog-to-digital converter circuit. Interface 2 is connected to one end of the platinum resistance RTD, and its other end is connected to analog switch one and resistor R8; resistor R8 is then connected to analog switch four and the non-inverting input of operational amplifier OP2, and the other end of analog switch four is grounded through resistor R11. Interface 3 is connected to the other end of the platinum resistance RTD, and its other end is connected to analog switch two and resistor R9; interface 4 is similarly connected to the other end of the platinum resistance RTD and connected to analog switch two. The other end of analog switch two is connected to the output of the constant current source circuit. The other end of resistor R9 is connected to the inverting input of operational amplifier OP2 and resistor R10, and resistor R10 and the output of operational amplifier OP2 are connected to resistor R12.

[0060] The second terminal of resistor R12 is connected to the first terminals of capacitors C4, C5, and R13, respectively; the second terminal of capacitor C4 is connected to the first terminal of resistor R14; the second terminal of resistor R13 is connected to the non-inverting input of operational amplifier OP3A and the first terminal of capacitor C6, respectively; the second terminals of capacitors C5 and C6, and the first terminal of resistor R15 are all grounded; the second terminal of resistor R15 is connected to the first terminal of resistor R16 and the inverting input of operational amplifier OP3A, respectively; the second terminal of resistor R14, the output terminal of operational amplifier OP3A, and the second terminal of resistor R16 are all connected to the inverting input of operational amplifier OP3B; the non-inverting input of operational amplifier OP3B is connected to a 2.5V reference voltage, the inverting input of operational amplifier OP3B is connected to its output terminal, and the output terminal of operational amplifier OP3B serves as the output terminal of the measurement circuit, which is ultimately connected to the analog-to-digital converter circuit.

[0061] Analog switches one through four all employ the TS3A5233 dual-channel analog switch, characterized by low on-resistance and low leakage current. Reference resistor R ref With an accuracy of 0.1% and a temperature drift of less than 10 ppm / °C, the stability of the measurement reference is ensured.

[0062] This measurement circuit, through a configurable interface combined with reference resistors, operational amplifiers, and filter circuits, can maintain high-precision sampling under different wiring methods and effectively suppress noise and system errors.

[0063] like Figure 5 As shown, the analog-to-digital converter circuit in this embodiment uses the AD7175-2 chip. This chip is a 24-bit Δ-Σ ADC that supports differential acquisition and can achieve 24-bit effective noise-free resolution at a sampling rate of 20 SPS. It has two pairs of differential channels and two GPIO interfaces, and can provide a 2.5 V reference voltage with a temperature drift of less than ±2 ppm / ℃ for the measurement circuit to use as a bias voltage.

[0064] The ports and pin definitions of the AD7175-2 chip are shown in the diagram below:

[0065] ADC_AIN0, ADC_AIN1, ADC_AIN2, ADC_AIN3, and ADC_AIN4 are analog input channels 0 to 4;

[0066] AIN0, AIN1, AIN2, AIN3, and AIN4 are analog signal input ports;

[0067] 2.5V_REF is a 2.5V reference voltage source;

[0068] REFOUT is the reference voltage output terminal;

[0069] REF+ and REF− are the positive and negative terminals of the reference voltage;

[0070] IOVDD is the digital input / output power supply, 3.3 volts;

[0071] AVDD1 and AVDD2 are analog power supply terminals, with a voltage of 5 volts.

[0072] DGND stands for digital ground;

[0073] AVSS is a simulated ground;

[0074] REGCAPA and REGCAPD are the capacitor connection terminals of the internal voltage regulator, used to stabilize the internal LDO voltage output;

[0075] 3.3V IOVDD is a 3.3V power supply input (digital section power supply).

[0076] 5.0V AVDD is a 5V power supply input (analog power supply).

[0077] XTAL1 and XTAL2 are external crystal oscillator pins used to connect to a crystal or an external clock signal;

[0078] XTAL2 / CLKIO are crystal oscillator outputs or clock inputs / outputs;

[0079] GPIO0 and GPIO1 are general-purpose input / output pins that can be configured via software.

[0080] S(-)Y(-)S(-)N(-)C(-)E(-)R(-)R(-)O(-)R(-) are the synchronization error indicator pins, which output a low-level signal when an error occurs in the chip;

[0081] CS stands for SPI Chip Select, used to select the ADC device for communication.

[0082] SCLK is the SPI clock signal line (Serial Clock).

[0083] DIN is the SPI data input line (data sent from the host to the ADC).

[0084] DOUT / RDY are SPI data output / data ready signal lines (data sent from the ADC to the host).

[0085] AD_CS, AD_CLK, AD_DIN, and AD_DOUT are the corresponding SPI interface signals on the microcontroller (MCU) side: chip select, clock, data input, and data output.

[0086] R72 100kΩ is a 100kΩ resistor used for pull-down current limiting;

[0087] AVDD is connected to two 1µF capacitors as power supply decoupling capacitors to filter out power supply noise;

[0088] The 1µF capacitor connected to REGCAPA and REGCAPD is the filter capacitor for the internal regulated output.

[0089] The REFOUT terminal is connected to a 1µF capacitor as a filter capacitor for the reference voltage output.

[0090] In this embodiment, pins AIN0 and AIN1 of the AD7175-2 are respectively connected to the reference resistor R. ref The two ends of the circuit are connected; pin AIN2 is connected to the output of the measurement circuit; pins GPIO0 and GPIO1 are connected to the A0 and A1 control terminals of the multiplexer ADG704 in the wiring adaptive identification circuit, respectively, to realize switch selection and channel configuration.

[0091] like Figure 6 The isolation module 3 in this embodiment includes an SPI isolation circuit and an I²C isolation circuit. The SPI isolation circuit connects to an analog-to-digital converter (ADC) circuit on one side and a signal processing module 4 on the other side, providing electrical isolation between the ADC circuit and the signal processing module 4. The SPI isolation circuit uses an ADuM1401 chip and its peripheral circuitry. The I²C isolation circuit connects to the signal processing module 4 on one side and a cold junction temperature measurement module 5 on the other side, used to collect the ambient temperature of the circuit board in real time and feed it back to the signal processing module 4. The I²C isolation circuit uses an ADuM1250 chip and its peripheral circuitry. The isolation circuits are powered by an isolated DC / DC power supply, isolating the data acquisition section and the microcontroller to meet the anti-interference requirements of industrial environments.

[0092] In this embodiment, the platinum resistance thermometer is defined as the hot junction, used to measure the temperature of the object under test; the circuit board environment is defined as the cold junction. The cold junction temperature measurement module 5 is a digital temperature sensor TMP117, with a typical accuracy of ±0.1°C within the room temperature range, and supports an I²C interface. In other embodiments of the present invention, the cold junction temperature measurement module 5 can also be implemented using a digital temperature sensor TMP119, whose accuracy can be further improved to ±0.08 °C.

[0093] In this embodiment, the signal processing module 4 is connected to the server / host computer 6 via a data cable or wireless network. The signal processing module 4 is a microcontroller, specifically an STM32F407VET6. It supports rich peripheral interfaces and a floating-point arithmetic unit, facilitating the implementation of complex algorithms. By integrating a third-order polynomial linearization algorithm, it calibrates coefficients online using the least squares method, supports power-on or timed self-calibration, optimizes polynomial coefficients, and stores them.

[0094] Example 2:

[0095] This embodiment provides a temperature measurement method based on the aforementioned adaptive wide-range platinum resistance high-precision temperature measuring device. After the device is powered on or reset, a wiring check is first performed to automatically identify the sensor's wiring method, and then the high-precision temperature measurement process begins. For example... Figure 7 As shown, the specific steps are as follows:

[0096] |S101, Power-on self-test and perform adaptive wiring identification;

[0097] |S102. Configure the analog switch according to the recognition result to form the corresponding measurement loop, and configure the measurement algorithm;

[0098] |S103. The platinum resistance is sampled multiple times with both forward and reverse constant current, and the multi-channel voltage is recorded. The system offset is eliminated by differential or averaging operations to obtain the resistance measurement value R. meas Meanwhile, the cold end temperature measurement module 5 collects the ambient temperature of the circuit board in real time and feeds it back to the signal processing module 4.

[0099] |S104, Signal processing module 4 performs linearization calculations based on the resistance measurement value to obtain the initial temperature, and then combines the cold junction temperature data and compensation model for correction, outputting the final temperature result; wherein, the compensation model is obtained by performing a calibration experiment in a constant temperature bath environment before temperature measurement, collecting error data at different circuit board temperatures and fitting it.

[0100] |S105. Upload the final temperature result to the server / host computer 6;

[0101] |S106, and proceed to the next measurement cycle according to a preset time interval (e.g., 1 minute or 5 minutes). The process supports multiple sampling averaging, which can effectively suppress noise and ensure data reliability.

[0102] The following is in conjunction with the appendix Figure 3-9 The specific process of temperature measurement is described below:

[0103] like Figure 3 , 4 As shown, the wiring adaptive identification function detects terminal connectivity by using a four-channel multiplexer ADG704 and a MOSFET Q1, combined with the GPIO pins of the analog-to-digital converter circuit to control the on / off state of the switch.

[0104] Specifically, such as Figure 3 As shown, when the system enters the wiring adaptive recognition stage, signal processing module 4 outputs a low level through the MCU_Collect pin, turning on MOSFET Q1, and... Figure 4 In the middle, analog switch three is open, and the A0 and A1 ports of ADG704 are controlled through the GPIO pin of the ADC to switch different channels in turn.

[0105] During this process, the system sequentially acquires the calibration voltage and the wiring voltage under different terminal combinations. By comparing the voltage values ​​and combining them with preset thresholds, it makes logical judgments to infer whether the sensor wiring method is two-wire, three-wire, or four-wire, thus achieving adaptive identification.

[0106] For calibration testing: First, disconnect all switches and measure the maximum voltage value as Vmax; then, close switch S4 and record the voltage at this moment as Vr; disconnect all switches, close S2, and record the voltage at this moment as Vm.

[0107] For wiring tests: Close switches S1 and S3 sequentially, and obtain the voltage after each closure. Based on Table 1, the current wiring pattern can be deduced.

[0108] Table 1. Correspondence between switch status and wiring mode:

[0109] Close switch Second-tier Third line Four lines S1 Vmax Vm Vm S3 Vmax Vmax Vr

[0110] Where R7 = R6, and different switch combinations of voltage are used to distinguish the wiring system.

[0111] This adaptive process requires no manual intervention, supports real-time re-detection, and improves system robustness.

[0112] After the wiring self-identification is completed, MCU_Collect outputs a high level, analog switch 3 is turned on, all pins of ADG704 are disconnected, and the system is ready to enter measurement mode.

[0113] Combination Figure 4 As shown, the two / three / four-wire measurement circuit uses a TS3A5233 dual-channel analog switch to adjust the mode. To avoid interference with the reference resistor R in measurement mode... ref To prevent interference with the identification mode, analog switch three should be in the open state before entering the measurement mode; after entering the measurement mode, analog switch three should be closed to connect the reference resistor to the circuit.

[0114] When performing a two-wire measurement, analog switch one is closed; when performing a three-wire or four-wire measurement, analog switch one is open.

[0115] Analog switch two controls the excitation path of the constant current source. When performing two-wire or three-wire measurements, analog switch two connects the constant current source to... Figure 4 When the "two / three wires" are conducting, the "four wires" channel is disconnected, and simultaneously, analog switch four is disconnected; when performing a four-wire measurement, analog switch two connects the constant current source to... Figure 4 The "four-wire" is turned on, the "two / three-wire" channel is disconnected, and at the same time, the simulated switch four is closed.

[0116] After the platinum resistance RTD is alternately excited by positive and negative constant current sources, the differential voltage is amplified differentially by operational amplifier OP2, processed by a low-pass filter circuit with a 10Hz cutoff, and a bias circuit based on the AD7175-2 2.5V reference voltage, before being sent to the analog-to-digital converter circuit. Reference resistor R ref (Accuracy 0.1%, temperature drift <10 ppm / °C) Connected in series in the current path for current calibration. The analog-to-digital converter uses the AD7175-2, achieving 24-bit effective noise-free resolution at 20 SPS. It supports simultaneous acquisition of voltage signals from the reference resistor and platinum resistance thermometer via two pairs of differential channels, enabling online calibration of the constant current source and ensuring temperature measurement accuracy. In three / four-wire mode, this circuit can also eliminate lead errors by balancing the wire resistance, ensuring measurement accuracy over long-distance transmission.

[0117] It should be noted that the typical on-resistance of the TS3A5233 is approximately 0.45 Ω (at 25°C and Vcc=5V), and its resistance value will fluctuate with temperature and current. If the internal resistance is Rm, when the constant current source current is 500 μA, the voltage across the internal resistance Rm is approximately 225 μV. This voltage level is well within the resolution range of the ADC and can be accurately captured.

[0118] In this embodiment, R8 = R11 = 50kΩ, R9 = R10 = 100kΩ are set to ensure that the leakage current at the differential amplifier input is minimized under the action of the excitation current. For Figure 3 and Figure 4The ADC acquisition channel voltages ADC_AIN0~ADC_AIN4 are simplified as V0, V1, V2, V3, and V4 respectively in the following description. Among them, ADC_AIN3 and ADC_AIN4 are used to form the second differential channel, corresponding to ADC_AIN0 and ADC_AIN1, and are used to simultaneously acquire the voltage of the reference resistor and the platinum resistance, thereby realizing the function of online calibration of the constant current source current value.

[0119] The analysis of the two-line system is as follows:

[0120] The resistance input to the system at this moment consists of a platinum resistance thermometer (RTD) and its lead resistance (R). w2 R w3 When the constant current source circuit receives a positive current I1, the following formula applies:

[0121]

[0122] It can be deduced that:

[0123]

[0124] Because the reference resistor R ref Given that the corrected forward current I1 and internal resistance Rm can be derived from [the given information], then V op2O The independent variables are RTD and R w2 and R w3 .

[0125] The three-wire system is analyzed as follows:

[0126] The resistors input to the system at this moment are divided into platinum resistance RTD and lead resistance R. w1 R w2 R w3 When the constant current source circuit receives a positive current I1, the following formula applies:

[0127]

[0128] It can be deduced that:

[0129]

[0130] When the constant current source input is a negative current I2, the following formula will apply:

[0131]

[0132] It can be deduced that:

[0133]

[0134] Because the constant current sources output equal current values ​​but opposite directions, this can be simplified to I1 = -I2 = I. For a platinum resistance RTD, R... w1 ≈R w3 We can obtain:

[0135] Therefore, we can deduce that:

[0136] Reference resistor R ref Since I and Rm can both be calculated, this equation can obtain the resistance value of the platinum resistance RTD with high accuracy, which in this example is the current resistance value of PT1000.

[0137] This invention employs positive and negative constant current source inputs, effectively eliminating system errors such as offset errors, thermoelectric effects, and 1 / f low-frequency noise in the measurement system by switching between positive and negative directions. Under unidirectional current, the operational amplifier offset voltage and thermocouple effect (caused by temperature gradients) introduce a fixed deviation, leading to inaccurate calculation of the platinum resistance RTD resistance value; by measuring in both positive and negative directions and taking the difference... These offsets cancel each other out, improving overall accuracy to ±0.02°C level from -50°C to +300°C. Furthermore, positive and negative averaging suppresses nonlinear errors in analog-to-digital conversion circuits and the effects of power supply ripple, ensuring accurate wire resistance compensation, especially in three / four-wire systems.

[0138] The analysis of the four-wire system is as follows:

[0139] The four-wire system uses Kelvin measurement, eliminating all lead wire interference. When the constant current source circuit input is a positive current I1, the following formula applies:

[0140]

[0141] Among them, R ref The reference resistor, Rm, is the on-resistance of the analog switch. V0 and V1 correspond to the voltages of ADC_AIN0 and ADC_AIN1, respectively, and are used to calculate I1 and Rm.

[0142] It can be deduced that:

[0143]

[0144] When the current reverses to I2, we have:

[0145]

[0146] Since I1 = -I2 = I, we can obtain:

[0147]

[0148] Therefore, the resistance value of the platinum resistance RTD is:

[0149]

[0150] The on-resistance of analog switch four (0.45 Ω) is much smaller than that of R8 to R11 (50 kΩ level), and the voltage drop at 500 μA current is only about 0.225 mV, which is negligible relative to the signal amplitude. Therefore, the theoretical accuracy can reach ±0.01°C.

[0151] The voltage output from operational amplifier OP2 is amplified and filtered by operational amplifier OP3A, and then a 2.5V DC bias is added by operational amplifier OP3B, enabling the analog-to-digital converter circuit to obtain a clean 0~5V positive signal.

[0152] In this embodiment, since platinum resistance thermometers (RTDs) are commonly used in the RTD industry between -50°C and +300°C, the resistance value within this temperature range is 803Ω to 2121Ω. At 150°C, the resistance is 1573Ω, therefore a reference resistor R can be selected. ref The resistance is 1600Ω. If the output current of the constant current source circuit is set to ±500 μA, then the voltage range V output by operational amplifier OP2 will be... op2O The voltage range is approximately ±0.45 V. To ensure accuracy, the voltage is amplified in operational amplifier OP3A. The amplification factor mainly depends on resistors R15 and R16, where R15 = 10kΩ and R16 = 4kΩ. These two resistors are high-precision resistors to ensure accurate amplification. This amplifies the voltage by a factor of 5, resulting in a range of approximately ±2.25V. This voltage is input to the negative terminal of operational amplifier OP3B. Therefore, the voltage at ADC_AIN2 is V2 = 2.5V – 5*V. op2O ,so:

[0153]

[0154] Furthermore, if it is necessary to expand the detection range, the output current value of the constant current source can be reduced or the amplification factor can be decreased (adjust the R16 / R15 ratio or R...). ref (Resistance), but this will reduce measurement accuracy; to improve accuracy, the amplification factor can be increased, but the detection range will decrease. In practical applications, it can be flexibly configured according to the target temperature range to balance measurement accuracy and detection range.

[0155] Using the method described above, the STM32 can calculate the resistance value of the platinum resistance thermometer (RTD). Then, based on the Callendar-Van Dusen equation or a lookup table, the measured resistance value of the RTD can be converted to the hot junction temperature.

[0156] Furthermore, considering that even with high precision constant current source circuits and analog-to-digital converter circuits in high-precision platinum resistance temperature measurement systems, the core components of the circuit board (constant current source, reference resistor, operational amplifier, ADC, etc.) will still drift due to changes in ambient temperature. To further improve the sampling accuracy of the system, this embodiment introduces a cold junction compensation mechanism to correct the impact of circuit board temperature drift on the measurement link. However, it should be noted that cold junction compensation increases detection time, hardware costs, and subsequent maintenance costs; therefore, it is typically only enabled in ultra-high precision measurement scenarios.

[0157] Before temperature measurement, the system collected error data at different plate temperatures through a constant temperature bath calibration experiment, and then adopted... The calibration was obtained through experimental fitting. The specific calibration procedure is as follows: Figure 8 As shown:

[0158] S201. Start the calibration procedure;

[0159] S202. Place the measuring board and PT1000 together in a constant temperature chamber / bath. Then, measure the resistance value Rmeas of PT1000 multiple times using a constant current source and acquisition circuit.

[0160] S203, and then convert it to obtain the reference temperature Tref;

[0161] S204. Combine this with the set temperature of the constant temperature chamber to form a calibration sample pair (Rmeas, Tref).

[0162] S205, Store calibration data in cache;

[0163] S206. Determine if the number of samples meets the minimum requirement: If the requirement is met, proceed to the next step; otherwise, return to step S202.

[0164] S207. Construct a third-order polynomial model; its calculation formula is:

[0165]

[0166] in, It measures the cold end temperature of the plate, and a0~a3 are calibration coefficients;

[0167] S208. Solve for the calibration coefficients a0~a3 using the least squares method; store a0~a3 in the microcontroller STM32F407VET6.

[0168] S209, Update system compensation coefficient

[0169] S210, End calibration process.

[0170] In this embodiment of the invention, the microcontroller simultaneously measures the cold junction temperature (the environment in which the platinum resistance RTD is located) while acquiring the hot junction temperature, and calculates the drift compensation value according to the calibration formula. The final temperature calculation is performed, and the specific process is as follows: Figure 9 As shown:

[0171] S300, Start measurement. At this time, the wiring configuration is detected synchronously and the corresponding algorithm is matched.

[0172] S311, the constant current source circuit 23 outputs a stable current to excite the platinum resistance RTD, which is PT1000 in this embodiment;

[0173] S312, Collect the voltage of the platinum resistance RTD;

[0174] S313. Calculate the resistance of the platinum resistance thermometer RTD;

[0175] S314. Convert to temperature value according to the Callendar-Van Dusen equation. ;

[0176] S321. Read the data information detected by the cold junction temperature measurement module 5;

[0177] S322. Obtain board temperature data based on data information. ;

[0178] S323. Calculate the drift compensation value according to the calibration formula. ;

[0179] S330. Based on the target temperature value obtained in step S314 and the compensation value obtained in step S323, the temperature is corrected, and the final temperature is calculated using the following formula:

[0180]

[0181] S340: Output the final temperature value and upload it to the server / host computer 6;

[0182] The above measurements and calculations eliminated drift errors caused by changes in ambient temperature. Ultra-high precision temperature data can be obtained using three-wire or four-wire measurements. If cold junction compensation is not enabled, the compensation value... The default value is 0.

[0183] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A platinum resistance high-precision temperature measuring device capable of automatically identifying the wiring mode, characterized in that, The power module, the signal detection module, the isolation module, the signal processing module and the cold-end temperature measurement module are included. The power module is used for powering the signal detection module, the cold-end temperature measurement module and the signal processing module. The signal detection module is connected with the signal processing module through the isolation module. The signal detection module includes a sensing probe, a wiring adaptive identification circuit, a constant current source circuit, a measurement circuit and an analog-to-digital conversion circuit. The sensing probe is used for collecting temperature signals of a measured object. The wiring adaptive identification circuit is used for identifying wiring modes of the sensing probe and feeding back identification results to the signal processing module. The constant current source circuit is used for providing stable current excitation to the sensing probe. The measurement circuit is used for processing voltage signals fed back by the sensing probe and sending the processed signals to the analog-to-digital conversion circuit. The analog-to-digital conversion circuit converts received analog signals into digital signals and transmits the digital signals to the signal processing module through the isolation module. The cold-end temperature measurement module is used for collecting ambient temperatures around the device in real time and feeding back the ambient temperatures to the signal processing module. The signal processing module calls corresponding temperature calculation methods according to wiring identification results, combines compensation data of the cold-end temperature measurement module, processes measured signals and obtains final temperature data.

2. The platinum resistance high-precision temperature measuring device of claim 1, wherein, The constant current source circuit is an improved Howland constant current source structure, which is composed of a differential amplification unit, a feedback network and a filter element, and is connected with a digital-to-analog conversion circuit at an input end and is used for outputting stable bidirectional current according to a control signal.

3. The platinum resistance high-precision temperature measuring device of claim 1, wherein, The sensing probe is a platinum resistance, and its model is PT100, PT500 or PT1000.

4. The platinum resistance high-precision temperature measuring device of claim 1, wherein, The wiring adaptive identification circuit includes a multiplexing switch, a level sampling circuit and a control switch. An input end of the multiplexing switch is connected with each port of the platinum resistance, and an output end is connected with a sampling end of the analog-to-digital conversion circuit. The level sampling circuit is used for obtaining voltage information under different switch combinations. The control switch is controlled by the signal processing module and is used for dynamically changing wiring modes and judging whether the sensor is connected in a two-wire system, a three-wire system or a four-wire system according to the sampling voltage.

5. The platinum resistance high-precision temperature measuring device of claim 1, wherein, The measurement circuit includes a differential amplification circuit, a low-pass filter circuit and a bias circuit connected in sequence, and the measurement circuit inputs voltage signals fed back by the sensing probe after differential amplification, filtering and biasing.

6. The high-precision temperature measuring device of claim 5, wherein the device is characterized by, The measurement circuit includes a plurality of input ports, a controllable analog switch, a reference resistance and a plurality of amplification and filtering circuits. The reference resistance forms a bridge circuit with the sensing probe and simultaneously serves as a reference input of the analog-to-digital conversion circuit. The differential amplification circuit is used for collecting voltage differences between two ends of the sensing probe. The low-pass filter is a second-order Bessel structure and is used for suppressing high-frequency noise. A direct current reference voltage is connected to an output end, so that signal zero point biasing is realized.

7. The platinum resistance high-precision temperature measuring device of claim 1, wherein, The analog-to-digital conversion circuit is a high-resolution Σ-Δ analog-to-digital converter, which has a plurality of differential input ports and is connected with the wiring identification circuit through general input and output pins.

8. The platinum resistance high-precision temperature measuring device of claim 1, wherein, The isolation module includes: An SPI isolation circuit is used for digital isolation between the analog-to-digital conversion circuit and the signal processing module. An I2C isolation circuit is used for isolation communication between the signal processing module and the cold-end temperature measurement module. The cold junction temperature measurement module is used for measuring the ambient temperature in real time and compensating the system temperature measurement result.

9. A temperature measurement method, characterized by, The temperature measurement method is implemented based on the platinum resistance high-precision temperature measurement device with automatic identification of wiring modes according to any one of claims 1-8, and comprises the following steps: Step one, power-on self-test and wiring identification; Step two, configuring an analog switch to form a measurement loop according to the identification result; Step three, sampling the platinum resistance multiple times with forward constant current and reverse constant current respectively, recording multi-channel voltage, and obtaining the resistance measurement value through difference or average operation; at the same time, the cold junction temperature measurement module is used to collect the circuit board ambient temperature in real time; Step four, the signal processing module applies a linearization formula to the resistance measurement value to calculate the initial measurement temperature; then, in combination with the cold junction temperature data and the preset compensation model, the initial measurement temperature is corrected to output the final temperature result.

10. The temperature measurement method according to claim 9, wherein The compensation model is obtained through calibration experiments in a constant temperature tank, that is, measurement error data is collected at different ambient temperatures, and a fitting model is constructed based on the error data; the signal processing module uses the compensation model to comprehensively operate the resistance measurement value and the cold junction temperature data, thereby realizing compensation of the system drift and obtaining the corrected temperature output.

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