Temperature measurement method and temperature measurement system based on platinum resistance temperature sensor

Abstract

The application provides a temperature measurement method and system based on a platinum resistance temperature sensor, generates a variable frequency square wave signal, outputs a modulated excitation current signal in the high level stage of the square wave signal, excites the platinum resistance temperature sensor through the modulated excitation current signal, transforms the time domain digital voltage signal to the power signal in the frequency domain through the FFT algorithm, extracts the direct current component and the fundamental wave component of the modulated excitation current signal, obtains the resistance value of the platinum resistance temperature sensor according to the direct current component and the fundamental wave component, and then calculates the temperature value of the measured point. The application uses the variable frequency square wave modulated current source to excite the platinum resistance, converts the resistance signal into the variable frequency square wave voltage signal, after the ADC collection, the single-chip microcomputer uses the method based on the FFT frequency domain analysis, can effectively remove the signal interference, and improves the accuracy of the temperature measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of temperature measurement, in particular to a temperature measurement method and system based on a platinum resistance temperature sensor, mainly used in the water supply and return water temperature collection system in the heat exchange station in the central heating industry. BACKGROUND

[0002] In the heating system, the balance of the secondary pipe network is mainly relied on the design of the pipe network itself or manual adjustment according to experience. Generally, a manual regulating valve is installed on site, and relevant personnel of the heat supply company coarsely adjust the valve angle according to the outdoor temperature and their years of experience, which makes it difficult to balance the secondary pipe network of the heating system, especially in areas with long secondary pipe networks or large differences in terrain, resulting in over-heating for residents close to the heat exchange station and insufficient heating for residents at the end of the secondary pipe network, and the valve angle can only be coarsely adjusted according to experience, with limited adjustment times.

[0003] The prior art has begun to use a return water temperature collection module for real-time adjustment. For example, the heating unit balance valve control device of Chinese patent CN213119305U can monitor the inlet and return water temperatures of the unit pipe and then adjust the valve angle in real time according to the inlet and return water temperature difference or the inlet and return water average temperature, so that the front end and the end of the secondary pipe network can achieve heating balance. The temperature collection module of CN213119305U uses a PT100 temperature sensor, which is a traditional platinum resistance temperature sensor.

[0004] The traditional platinum resistance temperature measurement method converts the resistance signal of the platinum resistance into a direct current voltage signal by applying a constant current excitation source to the platinum resistance. Since the direct current voltage signal is easily affected by external electromagnetic interference, when the external electromagnetic environment of the test system is severe, the electromagnetic interference has a great influence on the direct current voltage signal, thereby affecting the accuracy of temperature measurement. The traditional method is to convert the value domain into the frequency domain by using the FFT software algorithm, extract only the data of the direct current component, and filter out the frequency domain with large interference, and then convert it into a temperature value. The traditional algorithm filtering is relatively single, and only part of the interference signal can be filtered out, with poor effect. SUMMARY

[0005] The present application provides a platinum resistance temperature sensor temperature measurement method and system capable of effectively removing signal interference.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

[0007] A platinum resistance temperature sensor temperature measurement method, comprising the following steps:

[0008] S1, generating a square wave signal;

[0009] S2, outputting a modulated excitation current signal in the high level stage of the square wave signal;

[0010] S3, exciting the platinum resistance temperature sensor by the modulated excitation current signal to convert the resistance signal into a digital voltage signal;

[0011] S4, converting the time-domain digital voltage signal into a power signal in the frequency domain by the FFT algorithm;

[0012] S5, extracting the DC component of the modulated excitation current signal and the fundamental component of the power signal, obtaining the resistance value of the platinum resistance temperature sensor according to the DC component and the fundamental component, and then calculating the temperature value of the measured point.

[0013] Further, the square wave signal is variable frequency, if the temperature value of the measured point fluctuates greatly in the current frequency square wave signal period, and the fluctuation range is greater than ±0.3℃, then the output frequency of the square wave signal is increased by 976.5Hz, the modulated excitation current signal is output again until the temperature value is stable.

[0014] The application also provides a temperature measurement system based on the platinum resistance temperature sensor, comprising:

[0015] A constant current source generation circuit for generating a constant current;

[0016] A modulation control circuit for outputting the constant current as a modulated excitation current signal;

[0017] A platinum resistance temperature sensor for receiving the modulated excitation current signal and converting the resistance signal into a digital voltage signal;

[0018] A voltage amplification conditioning circuit for amplifying the digital voltage signal and inputting it into an MCU;

[0019] An MCU, which sends a variable frequency square wave signal to the modulation control circuit, and the modulation control circuit outputs the modulated excitation current signal in the high level stage of the square wave signal; the MCU can convert the time-domain digital voltage signal into a power signal in the frequency domain, extract the DC component and the fundamental component of the modulated excitation current signal, obtain the resistance value of the platinum resistance temperature sensor according to the DC component and the fundamental component, and then calculate the temperature value of the measured point.

[0020] According to the above technical solution, the application uses a variable frequency square wave modulated current source to excite the platinum resistance, converts the resistance signal into a variable frequency square wave voltage signal, and after being collected by the ADC, the MCU uses the FFT frequency domain analysis method to effectively remove signal interference and improve the accuracy of temperature measurement. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Method flow chart for the temperature measurement method of the present application;

[0022] Figure 2 Time domain and frequency domain chart for the square wave signal;

[0023] Figure 3 Principle block diagram for the temperature measurement system of the present application;

[0024] Figure 4 Circuit diagram for the constant current source generating circuit in the present application;

[0025] Figure 5 Circuit diagram for the modulation control circuit in the present application. DETAILED DESCRIPTION

[0026] A preferred embodiment of the present application will be described in detail below with reference to the accompanying drawings.

[0027] The present application provides a temperature measurement method based on platinum resistance temperature sensor, wherein the excitation mode of the platinum resistance temperature sensor uses square wave modulation current source, the square wave modulation adopts square wave modulation with variable frequency, when it is found that the current modulation frequency fluctuates greatly, it indicates that the interference at the frequency point is large, the current signal needs to be modulated to a new frequency point, the timer parameter is automatically changed to generate square wave signal of new frequency; and FFT algorithm is used to extract the direct current component and the fundamental component of the modulation control signal, and the voltage value is calculated. Referring to Figure 1 , specifically comprising the following steps:

[0028] S1, generating square wave signal with variable frequency;

[0029] S2, outputting modulation excitation current signal at the high level stage of the square wave signal;

[0030] S3, extracting the direct current component of the modulation excitation current signal and the fundamental component of the power signal, and converting the resistance signal into digital voltage signal;

[0031] S4, transforming the time domain digital voltage signal into frequency domain power signal through FFT algorithm;

[0032] S5, extracting the direct current component of the power signal and the fundamental component of the modulation excitation current signal, obtaining the resistance value of the platinum resistance temperature sensor according to the direct current component and the fundamental component, and calculating the temperature value of the measured point.

[0033] The output modulation excitation current signal is constant current, which is 1mA constant current in the embodiment.

[0034] The square wave signal is set to be variable frequency, if the current modulation excitation current signal fluctuation is large, then the square wave signal of new frequency is regenerated, so that the influence of external electromagnetic interference can be effectively avoided.

[0035] Figure 2 It is the frequency domain amplitude corresponding to the first 31 harmonics of the modulation excitation current signal in the embodiment, if the temperature value of the measured point fluctuates more than ±0.3℃ in the current frequency square wave signal period, a new frequency square wave signal needs to be regenerated, the modulation circuit and software are used to adjust in the embodiment, the timer parameters are automatically changed by the software to generate the square wave signal of new frequency, the frequency point of the current is adjusted to the new frequency point, then the temperature value of the measured point in the next square wave signal period is measured, if the temperature value of the measured point still fluctuates more than ±0.3℃, the square wave signal of new frequency is continuously regenerated until the frequency domain amplitude values tend to be consistent, the frequency with small interference and stable frequency is obtained.

[0036] After the resistance signal is converted into the digital voltage signal, the digital voltage signal on the platinum resistance temperature sensor is amplified from mV level to V level for convenient calculation, and the voltage amplification conditioning circuit can be used, the specific structure of the circuit belongs to the prior art, and will not be described here.

[0037] As shown in Figure 2 , the time domain digital voltage signal is converted into the frequency domain power signal by the FFT algorithm in step S4, the FFT is the discrete Fourier transform algorithm, and the algorithm itself belongs to the prior art, and the time domain signal can be converted into the frequency domain signal by using the FFT in the MATLAB software.

[0038] In the power signal in the embodiment, the fundamental wave and the harmonic wave are included, the sine wave component equal to the longest period of the oscillation is called the fundamental wave, the direct current component of the modulation excitation current signal is the average value of the signal, which is a constant independent of time.

[0039] As shown in Figure 3 , the application also provides a temperature measuring system based on the platinum resistance temperature sensor, which comprises a constant current source generating circuit 10, a modulation control circuit 20, a platinum resistance temperature sensor 30, a voltage amplification conditioning circuit 40 and an MCU single-chip microcomputer 50.

[0040] The constant current source generating circuit 10 has an operational amplifier, resistors, capacitors and a PNP transistor for outputting a constant current of 1mA, and the specific circuit structure is shown in Figure 4 The constant current source generating circuit includes a first operational amplifier U1, a second operational amplifier U2, a PNP transistor Q1, a first resistor R13, a second resistor R15, a third resistor R16, a fourth resistor R17, a fifth resistor R12, a first capacitor C28, a second capacitor C29 and a first diode D3.

[0041] The one end of the first resistor R13 is connected to the voltage input terminal of the constant current source generating circuit and connected to the positive terminal of the first capacitor C28, the negative terminal of the first capacitor C28 is grounded, the other end of the first resistor R13 is connected to the midpoint of the one end of the second resistor R15, the positive terminal of the second capacitor C29 and the positive input terminal of the first operational amplifier U1, the other end of the second resistor R15 and the negative terminal of the second capacitor C29 are grounded, the negative input terminal of the first operational amplifier U1 is connected to the output terminal of the first operational amplifier U1, the midpoint of the one end of the third resistor R16 and the one end of the fifth resistor R12.

[0042] The midpoint of the other end of the third resistor R16 and the one end of the fourth resistor R17 is connected to the positive input terminal of the second operational amplifier U2, the other end of the fourth resistor R17 is grounded, the negative input terminal of the second operational amplifier U2 is connected to the midpoint of the other end of the fifth resistor R12 and the emitter of the PNP transistor Q1, the base of the PNP transistor Q1 is connected to the output terminal of the second operational amplifier U2, the collector of the PNP transistor Q1 is connected to the anode of the first diode D3, the cathode of the first diode D3 is connected to the input terminal of the modulation control circuit as the output terminal of the constant current source generating circuit.

[0043] The modulation control circuit 20 is used for outputting the constant current as a modulation excitation current signal, outputting a constant current of 1mA in the high level stage of the square wave, for exciting the platinum resistance temperature sensor, and converting the resistance signal into a voltage signal.

[0044] As shown in Figure 5 The modulation control circuit 20 includes a second diode D2, a sixth resistor R14, a seventh resistor R18, an eighth resistor R19, a first NPN transistor Q2, a second NPN transistor Q3 and a third NPN transistor Q4.

[0045] The anode of the second diode D2 is connected to the input terminal of the modulation control circuit and is connected to the collector of the second NPN transistor Q3, the cathode of the second diode D2 is connected to one end of the sixth resistor R14, the other end of the sixth resistor R14 is connected to the collector of the first NPN transistor Q2, the emitter of the first NPN transistor Q2 is grounded, the base of the first NPN transistor Q2 is connected to the base of the third NPN transistor Q4 and one end of the seventh resistor R18, the other end of the seventh resistor R18 is the input terminal of the square wave signal, the emitter of the second NPN transistor Q3 is the output terminal of the modulation excitation current signal of the modulation control circuit, the base of the second NPN transistor Q3 is connected to one end of the eighth resistor R19 and the collector of the third NPN transistor Q4, the emitter of the third NPN transistor Q4 is grounded, and the other end of the eighth resistor R19 is the voltage input terminal of the modulation control circuit.

[0046] In the embodiment, the platinum resistance temperature sensor 30 is used to receive the modulation excitation current signal and convert the resistance signal into a digital voltage signal.

[0047] The voltage amplification conditioning circuit 40 is used to amplify the mV-level voltage signal on the platinum resistance to a V-level signal to meet the ADC data acquisition of the single-chip microcomputer.

[0048] In the embodiment, the MCU single-chip microcomputer 50 delivers a variable frequency square wave signal to the modulation control circuit, and the modulation control circuit outputs the modulation excitation current signal in the high voltage stage of the square wave signal; the MCU single-chip microcomputer can convert the time-domain digital voltage signal into a frequency-domain power signal, extract the direct current component and the fundamental wave component of the modulation excitation current signal, obtain the resistance value of the platinum resistance temperature sensor according to the direct current component and the fundamental wave component, and then calculate the temperature value of the measured point.

[0049] The above-described embodiments are only used to describe the preferred embodiments of the present application, and are not used to limit the scope of the present application, and various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope of the claims of the present application.

Claims

1. A temperature measurement method based on a platinum resistance temperature sensor, characterized by, The method comprises the following steps: S1, generating a square wave signal; S2, outputting a modulated excitation current signal in the high level stage of the square wave signal; S3, exciting the platinum resistance temperature sensor by the modulated excitation current signal to convert the resistance signal into a digital voltage signal; S4, transforming the time-domain digital voltage signal into a frequency-domain power signal by an FFT algorithm; S5, extracting the DC component of the modulated excitation current signal and the fundamental component of the power signal, obtaining the resistance value of the platinum resistance temperature sensor according to the DC component and the fundamental component, and then calculating the temperature value of the measured point; The square wave signal is variable frequency, if the temperature value of the measured point fluctuates greatly in the current frequency square wave signal period, and the fluctuation range is greater than ±0.3℃, then the output frequency of the square wave signal is increased by 976.5Hz, the modulated excitation current signal is output again until the temperature value is stable.

2. The temperature measurement method according to claim 1, wherein The modulated excitation current signal is a constant current of 1mA.

3. The temperature measurement method according to claim 1, wherein After step S3, the digital voltage signal on the platinum resistance temperature sensor is amplified from mV level to V level.

4. A temperature measurement system based on a platinum resistance temperature sensor, characterized in that It comprises: A constant current source generation circuit for generating a constant current; A modulation control circuit for outputting the constant current as a modulated excitation current signal; A platinum resistance temperature sensor for receiving the modulated excitation current signal and converting the resistance signal into a digital voltage signal; A voltage amplification conditioning circuit for amplifying the digital voltage signal and inputting it into an MCU; And An MCU which sends a variable frequency square wave signal to the modulation control circuit, the modulation control circuit outputs the modulated excitation current signal in the high level stage of the square wave signal, the MCU can transform the time-domain digital voltage signal into a frequency-domain power signal, extract the DC component and the fundamental component of the modulated excitation current signal, obtain the resistance value of the platinum resistance temperature sensor according to the DC component and the fundamental component, and then calculate the temperature value of the measured point.

5. The temperature measurement system of claim 4, wherein, The constant current source generation circuit comprises a first operational amplifier U1, a second operational amplifier U2, a PNP transistor Q1, a first resistor R13, a second resistor R15, a third resistor R16, a fourth resistor R17, a fifth resistor R12, a first capacitor C28, a second capacitor C29 and a first diode D3; One end of the first resistor R13 is connected to the voltage input end of the constant current source generation circuit and connected to the positive electrode end of the first capacitor C28, the negative electrode end of the first capacitor C28 is grounded, the other end of the first resistor R13 is connected to the midpoint of one end of the second resistor R15, the positive electrode end of the second capacitor C29 and the positive input end of the first operational amplifier U1, the other end of the second resistor R15 and the negative electrode end of the second capacitor C29 are grounded, the negative input end of the first operational amplifier U1 is connected to the output end of the first operational amplifier U1, the midpoint of one end of the third resistor R16 and one end of the fifth resistor R12; The other end of the third resistor R16 and one end of the fourth resistor R17 are connected to the positive input terminal of the second operational amplifier U2, the other end of the fourth resistor R17 is grounded, the negative input terminal of the second operational amplifier U2 is connected to the other end of the fifth resistor R12 and the midpoint of the emitter of the PNP transistor Q1, the base of the PNP transistor Q1 is connected to the output terminal of the second operational amplifier U2, the collector of the PNP transistor Q1 is connected to the anode of the first diode D3, and the cathode of the first diode D3 is connected to the input terminal of the modulation control circuit as the output terminal of the constant current source generating circuit.

6. The temperature measurement system of claim 4, wherein, The modulation control circuit comprises a second diode D2, a sixth resistor R14, a seventh resistor R18, an eighth resistor R19, a first NPN transistor Q2, a second NPN transistor Q3, and a third NPN transistor Q4. The anode of the second diode D2 is connected to the collector of the second NPN transistor Q3 as the input terminal of the modulation control circuit, the cathode of the second diode D2 is connected to one end of the sixth resistor R14, the other end of the sixth resistor R14 is connected to the collector of the first NPN transistor Q2, the emitter of the first NPN transistor Q2 is grounded, the base of the first NPN transistor Q2 is connected to the base of the third NPN transistor Q4 and the midpoint of one end of the seventh resistor R18, the other end of the seventh resistor R18 is connected to the input terminal of the square wave signal, the emitter of the second NPN transistor Q3 is connected to the output terminal of the modulation excitation current signal of the modulation control circuit, the base of the second NPN transistor Q3 is connected to the midpoint of one end of the eighth resistor R19 and the collector of the third NPN transistor Q4, the emitter of the third NPN transistor Q4 is grounded, and the other end of the eighth resistor R19 is connected to the voltage input terminal of the modulation control circuit.

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