Thermocouple signal simulation circuit design method
By designing a power supply module, input module, subtraction module, isolation amplification module, and signal generation module in synergy, the problems of multi-point simulation and low accuracy in existing thermocouple signal simulation technologies are solved, achieving high-precision and low-cost thermocouple signal simulation, which is suitable for temperature measurement and calibration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-27
- Publication Date
- 2026-03-13
AI Technical Summary
Existing thermocouple signal simulation methods have limitations such as being able to simulate only a single temperature point, having complex circuit designs, low simulation accuracy, and using non-floating power supply signals, making it difficult to meet the requirements of multi-point simulation and high precision.
A thermocouple signal simulation circuit was designed, comprising a power supply module, an input module, a subtraction module, an isolation amplification module, and a signal generation module. The circuit generates a floating, high-fidelity thermocouple signal through an isolated power supply and an isolation module. It is suitable for 4–20mA current command signals or 1–5V voltage command signals and simulates -6–50mV thermocouple signals within a temperature measurement range of -200–1200℃.
It achieves high-precision, low-cost thermocouple signal simulation, which can replace real thermocouple sensors, improve the efficiency and reliability of testing and calibration, and generate highly realistic signals that are easy to operate.
Smart Images
Figure CN121659876A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electronic circuit design technology and relates to a method for designing a thermocouple signal analog circuit. Technical Background
[0002] In the development, debugging, and testing phases of temperature acquisition systems or temperature control devices, thermocouple signals are often used as input signals to verify their performance. Currently, common methods for simulating thermocouple signals mainly include the following two: One method generates a fixed voltage using a voltage divider circuit or a reference power supply. The drawback of this method is that it can only simulate thermocouple signals at a single temperature point. The other method uses a digital-to-analog converter (DAC) combined with microcontroller control to output the voltage value corresponding to the thermocouple through a lookup table. While this method can achieve multi-point simulation, it suffers from complex circuit design and low simulation accuracy. Furthermore, the thermocouple signals simulated by these two methods are not floating signals for the power supply, thus limiting their application. Summary of the Invention
[0003] This invention proposes a low-cost, high-precision, and high-fidelity thermocouple signal simulation circuit design method. The supply voltage range is 7.2–30.7V. Based on a 4–20mA current command signal or a 1–5V voltage command signal, it can simulate and generate a -6–50mV floating thermocouple signal corresponding to a temperature measurement range of -200–1200℃, suitable for research and development, production, and calibration. The thermocouple signal simulation circuit includes:
[0004] The power supply module provides two isolated ±5V power supplies and a 1.5V regulated power supply to meet the operating requirements of each functional module.
[0005] The input module is used to convert the input 4-20mA current command signal into a 1-5V voltage command signal, or it can directly input a 1-5V voltage command signal;
[0006] The subtraction module subtracts the 1-5V voltage command signal from the input module from the 1.5V reference voltage, and outputs a voltage signal of -0.5-3.5V.
[0007] The isolation amplifier module is used to isolate the -0.5 to 3.5V voltage signal output by the subtraction module, resulting in a floating -0.181 to 1.118V differential signal that is completely isolated from the preceding circuit.
[0008] The signal generation module amplifies the -0.181 to 1.118V differential signal output by the isolation amplification module and outputs an analog thermocouple signal of -6 to 50mV corresponding to the temperature measurement range of -200 to 1200℃.
[0009] The power module includes a 5V power supply 5V1 and its inverting circuit, an isolated 5V power supply 5V2 and its inverting circuit, and a 1.5V voltage regulator circuit. The 5V power supply 5V1 circuit converts a supply voltage in the range of 7.2 to 30.7V into a 5V voltage. The isolated 5V power supply 5V2 circuit generates an isolated 5V2 voltage based on the 5V1 power supply, with its power ground being GND2, which is physically isolated from the 5V1 power supply ground GND1. The 5V1 power supply inverting circuit inverts the 5V1 power supply to obtain a -5V1 power supply, with its power ground being GND1. The 5V2 power supply inverting circuit inverts the 5V2 power supply to obtain a -5V2 power supply, with its power ground being GND2. The 1.5V voltage regulator circuit generates a stable 1.5V voltage signal based on the 5V1 power supply, with its reference ground being GND1.
[0010] Furthermore, the input module includes an instruction signal input terminal AIN, a jumper pin JP1, and a resistor R4; one pin of the jumper pin JP1 is connected to the instruction signal input terminal AIN, and the other pin of the jumper pin JP1 is connected to one end of the resistor R4; the other end of the resistor R4 is connected to the power ground GND1; if the signal of the instruction signal input terminal AIN is a current instruction signal of 4-20mA, the two pins of the jumper pin JP1 are shorted with a shorting cap to convert the instruction signal into a voltage instruction signal of 1-5V; if the input instruction signal is a voltage instruction signal of 1-5V, the two pins of the jumper pin JP1 are not shorted.
[0011] Furthermore, the subtraction module includes an operational amplifier U7, resistors R5, R6, R7, and R8; pin 7 of operational amplifier U7 is connected to a 5V1 power supply, and pin 4 of operational amplifier U7 is connected to a -5V1 power supply; one end of resistor R6 is connected to the signal input terminal AIN; the other end of resistor R6 and one end of resistor R8 are connected to the non-inverting input terminal of pin 3 of operational amplifier U7; the other end of resistor R8 is connected to power ground GND1; one end of resistor R5 is connected to the 1.5V regulated voltage terminal; the other end of resistor R5 and one end of resistor R7 are connected to the inverting input terminal of pin 2 of operational amplifier U7; the other end of resistor R7 is connected to the output terminal of pin 6 of operational amplifier U7, serving as the output terminal of the subtraction module, and connected to the input terminal of the isolation module.
[0012] Furthermore, the isolation amplification module includes an isolation chip U5, capacitors C10, C11, C12, C13, and C14, and a resistor R9; one end of resistor R9 is connected to the output terminal of the subtraction module; the other end of resistor R9 is connected to the second pin of the isolation chip U5; the third pin of the isolation chip U5, one end of capacitor C10, one end of capacitor C11, and a 5V1 power supply are connected; the fourth pin of the isolation amplification chip U5, the other end of capacitor C10, the other end of capacitor C11, and the power ground GND are connected. 1. Connect the capacitor C12 to pin 1 of the isolation chip U5; 2. Connect the capacitor C12 to ground GND1; 3. Connect pin 8 of the isolation chip U5, one end of capacitor C13, one end of capacitor C14, and power supply 5V2; 4. Connect pin 5 of the isolation chip U5, the other end of capacitor C13, the other end of capacitor C14, and power supply GND2; 5. Output the positive phase of the differential signal from pin 7 of the isolation chip U5; 6. Output the negative phase of the differential signal from pin 6 of the isolation chip U5.
[0013] Furthermore, the signal generation module includes an operational amplifier U8, resistors R10, R11, R12, and R13; pin 7 of operational amplifier U8 is connected to a 5V2 power supply, and pin 4 of operational amplifier U8 is connected to a negative power supply -5V2; one end of resistor R11 is connected to the positive-inverting signal output by the isolation amplifier module; the other end of resistor R11 and one end of resistor R13 are connected to the non-inverting input pin 3 of operational amplifier U8; the other end of resistor R13 is connected to ground GND2; one end of resistor R10 is connected to the negative-inverting signal output by the isolation amplifier module; the other end of resistor R10 and one end of resistor R12 are connected to the inverting input pin 2 of operational amplifier U8; the other end of resistor R12 is connected to the output pin 6 of the operational amplifier, outputting an analog thermocouple signal.
[0014] Furthermore, the 5V power supply 5V1 circuit includes a diode D1, a linear regulator U1, a capacitor C1, and a capacitor C2; one end of the diode D1 is connected to the power supply VCC; the other end of the diode D1 and one end of the capacitor C1 are connected to the second input terminal of the linear regulator U1; the other end of the capacitor C1 and the third ground pin of the linear regulator U1 are connected to the power ground GND1; one end of the capacitor C2 is connected to the power ground GND1; the first output terminal of the linear regulator is connected to the other end of the capacitor C2, providing a 5V power supply 5V1.
[0015] Furthermore, the isolated 5V power supply 5V2 circuit includes a power isolation chip U2, a capacitor C3, and an inductor L1; one end of the capacitor C3 and one end of the inductor L1 are connected to the 5V1 power supply; the other end of the capacitor C3, the first pin VIN- of the power isolation chip U2, and the power ground GND1 are connected; the other end of the inductor L1 is connected to the second pin VIN+ of the power isolation chip U2; the fifth pin VOUT+ of the power isolation chip U2 provides the isolated power supply 5V2; and the fourth pin VOUT- of the power isolation chip U2 provides the isolated power ground GND2.
[0016] Furthermore, the 5V power supply 5V1 inverting circuit includes a voltage converter chip U3, polarized capacitors C4, C5, and C6; the first pin (BOOST), the eighth pin (V+), and the positive terminal of polarized capacitor C6 of the voltage converter chip U3 are connected to the 5V1 power supply; the negative terminal of polarized capacitor C6, the third pin (GND), and the positive terminal of polarized capacitor C5 are connected to the power ground (GND1); the second pin (CAP+) of the voltage converter chip U3 is connected to the positive terminal of polarized capacitor C4; the negative terminal of polarized capacitor C4 is connected to the fourth pin (CAP-) of the voltage converter chip U3; and the fifth pin (VOUT) of the voltage converter chip U3 is connected to the negative terminal of polarized capacitor C5, providing a negative power supply -5V1.
[0017] Furthermore, the 5V power supply 5V2 inverting circuit includes a voltage converter chip U4, polarized capacitors C7, C8, and C9; the first pin (BOOST), the eighth pin (V+), and the positive terminal of polarized capacitor C9 are connected to the 5V2 power supply; the negative terminal of polarized capacitor C9, the third pin (GND), and the positive terminal of polarized capacitor C8 are connected to the power ground (GND2); the second pin (CAP+) of voltage converter chip U4 is connected to the positive terminal of polarized capacitor C7; the negative terminal of polarized capacitor C7 is connected to the fourth pin (CAP-) of voltage converter chip U4; and the fifth pin (VOUT) of voltage converter chip U4 is connected to the negative terminal of polarized capacitor C8, providing a negative power supply -5V2.
[0018] Furthermore, the 1.5V voltage regulator circuit includes a voltage reference chip U6, resistors R1, R2, and R3; the first pin (R pin) and the third pin (K pin) of the voltage reference chip U6, one end of resistor R2, and one end of resistor R1 are connected; the second pin (A pin) of the voltage reference chip U6 is connected to power ground GND1; the other end of resistor R1 is connected to power supply 5V1; the other end of resistor R2 is connected to one end of resistor R3; the other end of resistor R3 is connected to power ground GND1; resistors R2 and R3 form a voltage divider circuit, providing a stable 1.5V voltage signal at the connection point of resistors R2 and R3.
[0019] The present invention has the following beneficial effects:
[0020] 1. This invention achieves the simulated generation of -6 to 50mV thermocouple signals corresponding to the temperature measurement range of -200 to 1200℃ through the synergistic effect of the input module, subtraction module, isolation amplification module and signal generation module.
[0021] 2. Using isolated power supplies and isolation modules, a floating, high-fidelity thermocouple analog signal is generated.
[0022] 3. This invention has good accuracy and ease of operation, and can efficiently replace real thermocouple sensors, improving the efficiency and reliability of testing and calibration work.
[0023] 4. Thermocouple signals can be simulated using only conventional electronic components, which is low-cost and conducive to mass production. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the thermocouple signal analog circuit of the present invention.
[0025] Figure 2 This is a circuit structure diagram of the input module, subtraction module, isolation amplification module, and signal generation module in the thermocouple signal analog circuit of the present invention.
[0026] Figure 3 This is a circuit diagram of the power supply module in the thermocouple signal analog circuit of the present invention.
[0027] In the diagram, I - input module, II - subtraction module, III - isolation amplifier module, IV - signal generation module, V - 5V power supply 5V1 circuit, VI - isolation 5V power supply 5V2 circuit, VII - SV power supply 5V1 inverting circuit, VIII - 5V power supply 5V2 inverting circuit, and IX - 1.5V voltage regulator circuit. Detailed Implementation
[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0029] Combination Figure 2 As shown, this invention comprises an I-input module, a II-subtraction module, a III-isolation amplification module, and an IV-signal generation module. The input command signal is either a 4-20mA current signal or a 1-5V voltage signal. After passing through the input module, the command signal is uniformly converted into a 1-5V voltage signal. After processing by the subtraction and isolation amplification modules, a -0.181-1.118V floating differential signal is obtained. Finally, the signal generation module amplifies the differential signal, outputting a -6-50mV thermocouple signal corresponding to a temperature measurement range of -200-1200℃.
[0030] The input module includes an instruction signal input terminal AIN, jumper pin JP1, and resistor R4. The AIN terminal receives a 4–20mA current instruction signal. This signal is connected to ground GND1 via resistor R4 (250Ω) and then converted to a 1–5V voltage instruction signal at the AIN terminal. Simultaneously, the AIN terminal can also directly input a 1–5V voltage signal as the input signal for the entire circuit. If the instruction signal input terminal AIN receives a 4–20mA current instruction signal, the two pins of jumper pin JP1 are shorted using a shorting cap to convert the instruction signal into a 1–5V voltage instruction signal. If the input instruction signal is a 1–5V voltage instruction signal, the two pins of jumper pin JP1 are not shorted.
[0031] The subtraction module includes operational amplifier U7, resistors R5, R6, R7, and R8. The analog signal input terminal AIN has a voltage range of 1–5V. Because the temperature range includes temperatures below zero degrees Celsius, and thermocouple signals are negative voltage signals below zero, the input voltage command signal AIN needs to be biased. Consider subtracting a 1.5V reference voltage from AIN, making its voltage range -0.5 to 3.5V. The 1.5V reference voltage is connected to the inverting input of the operational amplifier through resistor R5. Resistors R6 and R8 form a voltage divider network, proportionally dividing the input voltage command signal AIN and connecting it to the non-inverting input of the operational amplifier. Resistor R7 acts as a feedback resistor, connected between the output and inverting input of the operational amplifier, forming a negative feedback loop to ensure the linear amplification characteristics of the circuit. The output voltage of operational amplifier U7 is the difference between the input voltage AIN and the reference voltage 1.5V. Let Vin be the voltage at the analog signal input terminal AIN, V- be the potential at the inverting input terminal (pin 2) of operational amplifier U7, V+ be the potential at the non-inverting input terminal (pin 3), and Vo be the output of the subtraction module (pin 7). The relationship between the input and output of the subtraction module can be derived as follows.
[0032] The input current at the non-inverting input of operational amplifier U7 is 0, therefore,
[0033]
[0034] Because the inverting and non-inverting inputs of operational amplifier U7 are equal, i.e., V- = V+, formula (1) can be written as follows:
[0035]
[0036] Similarly, since the input current at the inverting input of operational amplifier U7 is 0, therefore,
[0037]
[0038] Among them, resistors R5, R6, R7, and R8 have the same resistance value. Combining equations (2) and (3), we can obtain the output Vo of the subtraction module.
[0039] V o =V in -1.5V (4)
[0040] The isolation amplifier module includes an isolation amplifier chip ISO224(U5), capacitors C10, C11, C12, C13, C14, and resistor R9. Among them, resistor R9 is connected to the output terminal of the subtraction module on the left and to the second input terminal of the isolation amplifier chip U5 on the right, and is used to limit the input current; capacitors C10 and C11 are connected in parallel between the power supply 5V1 and the power ground GND1, and are used to decouple and filter the input power supply to filter out power supply noise of different frequency bands; capacitor C12 is connected between the VCAP pin of ISO224 and ground, and is used as the energy storage capacitor of the isolated charge pump to ensure the stable operation of the internal isolation circuit of the chip; capacitors C13 and C14 are connected in parallel between the 5V power supply 5V2 and the power ground GND2, and are used to decouple and filter the output power supply to filter out power supply noise of different frequency bands; the isolation amplifier chip ISO224 is used to isolate and amplify the analog voltage signal at the input terminal, and outputs a floating voltage signal that is completely electrically isolated from the input signal and proportional to it in differential form at the output terminal. The voltage range of this differential output signal is -0.181V to 1.118V. The voltage signal output by the subtraction module is isolated and amplified by the isolation amplification module, thereby obtaining a floating differential voltage signal with characteristics consistent with the real thermocouple signal.
[0041] The signal generation module includes operational amplifier U8, resistors R10, R11, R12, and R13. Resistor R10 is used to introduce the inverting input of the differential signal output from the isolation amplifier module to the inverting input of pin 2 of operational amplifier U8. Resistor R12 acts as a feedback resistor, connected between the output and inverting input of operational amplifier U8 to form a negative feedback loop, and works with resistor R10 to determine the amplification factor of the circuit. Resistors R11 and R13 form a voltage divider network, proportionally dividing the non-inverting input of the differential signal output from the isolation amplifier module before sending it to the non-inverting input of operational amplifier U8, thus providing a reference voltage for the operational amplifier. Under the action of negative feedback, operational amplifier U8 amplifies the differential voltage signal output from the isolation amplifier module, outputting a -6 to 50mV thermocouple analog signal corresponding to a temperature measurement range of -200 to 1200℃ at pin 6 of operational amplifier U8.
[0042] Combination Figure 3 The diagram shows the V-5V power supply 5V1 circuit, VI-isolated 5V power supply 5V2 circuit, VII-5V power supply 5V1 inverting circuit, VIII-5V power supply 5V2 inverting circuit, and IX-1.5V voltage regulator circuit of the present invention. The 5V power supply 5V1 circuit converts a supply voltage in the range of 7.2 to 30.7V to 5V. The isolated 5V power supply 5V2 circuit generates an isolated 5V2 voltage based on the 5V1 power supply, with its power ground being GND2, physically isolated from the 5V1 power supply ground GND1. The 5V1 power supply inverting circuit inverts the 5V1 power supply to obtain a -5V1 power supply, with its power ground being GND1. The 5V2 power supply inverting circuit inverts the 5V2 power supply to obtain a -5V2 power supply, with its power ground being GND2. The 1.5V voltage regulator circuit generates a stable 1.5V voltage signal based on the 5V1 power supply, with its reference ground being GND1.
[0043] The 5V power supply circuit includes diode D1, linear regulator U1, capacitor C1, and capacitor C2. Diode D1 is connected in series between the external power supply VCC and the regulator input to prevent reverse connection. When VCC polarity is correct, D1 conducts forward, providing the input voltage to the regulator; when VCC is reverse connected, D1 is cut off, blocking reverse current and protecting subsequent circuitry from damage. The second input terminal of regulator U1 receives the input voltage after D1, while the first output terminal provides a stable 5V1 power supply to drive subsequent circuitry. The ground terminal is connected to power ground GND1. Capacitor C1, connected in parallel with ground at the input terminal, filters out high-frequency interference and transient spikes, enhancing the regulator's ability to suppress input noise. Capacitor C2, connected in parallel with ground at the output terminal, stabilizes the output voltage, reduces ripple and noise, and improves the regulator's transient response performance under sudden load changes, thus ensuring the power supply remains stable and reliable under various operating conditions. To ensure the normal operation of the voltage regulator, the voltage of the external power supply VCC should be between 7.2 and 30.7V.
[0044] The 5V / 5V2 isolated power supply circuit includes a power isolation chip U2, a capacitor C3, and an inductor L1. The isolation chip U2 provides electrical isolation between the input and output power supplies. Pin 5 of U2 outputs a 5V2 power supply, while pin 4 outputs a power ground GND2, which is isolated from the power ground GND1. The input terminals form a filter network with inductor L1 and capacitor C3 to suppress high-frequency noise and power ripple.
[0045] The 5V power supply 5V1 inverting circuit includes a voltage converter chip MAX1044 (U3), polarized capacitors C4, C5, and C6. This circuit uses the MAX1044 charge pump chip U3 to convert the input positive voltage (+5V) to a negative voltage (-5V). Capacitor C4 acts as the charge pump capacitor, used for voltage inversion and transmission; capacitor C5 is used for output voltage filtering to improve the stability of the negative voltage; capacitor C6 is connected at the input for high-frequency decoupling and to suppress power supply noise. The CAP+ and CAP- pins of the MAX1044 are connected to capacitor C4. VOUT outputs the negative power supply -5V1, V+ is connected to the +5V power supply, GND is connected to the power ground GND1, and the BOOST pin is connected to the 5V1 power supply, which can increase the internal oscillation frequency by approximately 6 times, thereby reducing output impedance and output ripple.
[0046] The 5V / 5V2 inverting circuit includes a voltage converter chip MAX1044 (U4), polarized capacitors C7, C8, and C9. This circuit uses the MAX1044 charge pump chip U4 to convert the input positive voltage (+5V) to a negative voltage (-5V). Capacitor C7 acts as the charge pump capacitor, used for voltage inversion and transmission; capacitor C8 is used for output voltage filtering to improve the stability of the negative voltage; capacitor C9 is connected at the input for high-frequency decoupling and suppressing power supply noise. The CAP+ and CAP- pins of the MAX1044 are connected to capacitor C7. VOUT outputs the negative power supply -5V2, V+ is connected to the +5V power supply, GND is connected to the power ground GND2, and the BOOST pin is connected to the 5V2 power supply, which can increase the internal oscillation frequency by approximately 6 times, thereby reducing output impedance and output ripple.
[0047] The 1.5V voltage regulator circuit includes a voltage reference chip TL431 (U6), resistors R1, R2, and R3. The first pin (R) and the third pin (K) of the TL431 voltage reference chip are shorted to output a stable 2.5V reference voltage. Resistor R1 is a current-limiting component to prevent damage to the TL431 chip from overcurrent. Resistors R2 and R3 form a voltage divider circuit, providing a stable 1.5V voltage signal at the connection point of resistors R2 and R3.
Claims
1. A method for designing a thermocouple signal analog circuit, characterized in that, The power supply voltage range is 7.2~30.7V. It can simulate and generate a -6~50mV thermocouple signal corresponding to the temperature measurement range of -200~1200℃ based on a current command signal of 4~20mA or a voltage command signal of 1~5V.
2. The thermocouple signal analog circuit according to claim 1, characterized in that, The thermocouple signal analog circuit includes: The power supply module provides two isolated ±5V power supplies and a 1.5V regulated power supply to meet the operating requirements of each functional module. The input module is used to convert the input 4-20mA current command signal into a 1-5V voltage command signal, or it can directly input a 1-5V voltage command signal; The subtraction module subtracts the 1-5V voltage command signal from the input module from the 1.5V reference voltage, and outputs a voltage signal of -0.5-3.5V. The isolation amplifier module is used to isolate the -0.5 to 3.5V voltage signal output by the subtraction module, resulting in a floating -0.181 to 1.118V differential signal that is completely isolated from the preceding circuit. The signal generation module amplifies the -0.181 to 1.118V differential signal output by the isolation amplification module and outputs an analog thermocouple signal of -6 to 50mV corresponding to the temperature measurement range of -200 to 1200℃.
3. The thermocouple signal analog circuit according to claim 2, characterized in that, The power supply module includes a 5V power supply 5V1 and its inverting circuit, an isolated 5V power supply 5V2 and its inverting circuit, and a 1.5V voltage regulator circuit. The 5V power supply 5V1 circuit converts a supply voltage in the range of 7.2 to 30.7V into a 5V voltage. The isolated 5V power supply 5V2 circuit generates an isolated 5V2 voltage based on the 5V1 power supply, with its power ground being GND2, physically isolated from the 5V1 power supply ground GND1. The 5V1 power supply inverting circuit inverts the 5V1 power supply to obtain a -5V1 power supply, with its power ground being GND1. The 5V2 power supply inverting circuit inverts the 5V2 power supply to obtain a -5V2 power supply, with its power ground being GND2. The 1.5V voltage regulator circuit generates a stable 1.5V voltage signal based on the 5V1 power supply, with its reference ground being GND1.
4. A thermocouple signal analog circuit according to claim 2, characterized in that, The input module includes an instruction signal input terminal AIN, a jumper pin JP1, and a resistor R4. One pin of the jumper pin JP1 is connected to the instruction signal input terminal AIN, and the other pin of the jumper pin JP1 is connected to one end of the resistor R4. The other end of the resistor R4 is connected to the power ground GND1. If the instruction signal input terminal AIN is a current instruction signal of 4-20mA, the two pins of the jumper pin JP1 are shorted with a shorting cap to convert the instruction signal into a voltage instruction signal of 1-5V. If the input instruction signal is a voltage instruction signal of 1-5V, the two pins of the jumper pin JP1 are not shorted.
5. A thermocouple signal analog circuit according to claim 2, characterized in that, The subtraction module includes operational amplifier U7, resistors R5, R6, R7, and R8. Pin 7 of operational amplifier U7 is connected to a 5V1 power supply, and pin 4 of operational amplifier U7 is connected to a -5V1 power supply. One end of resistor R6 is connected to the signal input terminal AIN. The other end of resistor R6 and one end of resistor R8 are connected to the non-inverting input terminal (pin 3) of operational amplifier U7. The other end of resistor R8 is connected to power ground (GND1). One end of resistor R5 is connected to the 1.5V regulated voltage terminal. The other end of resistor R5 and one end of resistor R7 are connected to the inverting input terminal (pin 2) of operational amplifier U7. The other end of resistor R7 is connected to the output terminal (pin 6) of operational amplifier U7, serving as the output terminal of the subtraction module, and connected to the input terminal of the isolation module.
6. A thermocouple signal analog circuit according to claim 2, characterized in that, The isolation amplification module includes an isolation chip U5, capacitors C10, C11, C12, C13, and C14, and a resistor R9. One end of resistor R9 is connected to the output of the subtraction module; the other end of resistor R9 is connected to the second pin of isolation chip U5; the third pin of isolation chip U5, one end of capacitor C10, and one end of capacitor C11 are connected to a 5V1 power supply; the fourth pin of isolation amplification chip U5, the other end of capacitor C10, and the other end of capacitor C11 are connected to ground GND1. Connections are made as follows: one end of capacitor C12 is connected to pin 1 of isolation chip U5; the other end of capacitor C12 is connected to power ground GND1; pin 8 of isolation chip U5, one end of capacitor C13, one end of capacitor C14 are connected to power supply 5V2; pin 5 of isolation chip U5, the other end of capacitor C13, the other end of capacitor C14 are connected to power ground GND2; pin 7 of isolation chip U5 outputs the positive phase signal of the differential signal; pin 6 of isolation chip U5 outputs the negative phase signal of the differential signal.
7. A thermocouple signal analog circuit according to claim 2, characterized in that, The signal generation module includes an operational amplifier U8, resistors R10, R11, R12, and R13. Pin 7 of operational amplifier U8 is connected to a 5V2 power supply, and pin 4 is connected to a negative -5V2 power supply. One end of resistor R11 is connected to the positive-inverting signal output from the isolation amplifier module. The other end of resistor R11 and one end of resistor R13 are connected to the non-inverting input (pin 3) of operational amplifier U8. The other end of resistor R13 is connected to ground (GND2). One end of resistor R10 is connected to the negative-inverting signal output from the isolation amplifier module. The other end of resistor R10 and one end of resistor R12 are connected to the inverting input (pin 2) of operational amplifier U8. The other end of resistor R12 is connected to the output (pin 6) of the operational amplifier, outputting an analog thermocouple signal.
8. A thermocouple signal analog circuit according to claim 3, characterized in that, The 5V power supply circuit includes a diode D1, a linear regulator U1, a capacitor C1, and a capacitor C2. One end of the diode D1 is connected to the power supply VCC. The other end of the diode D1 and one end of the capacitor C1 are connected to the second input terminal of the linear regulator U1. The other end of the capacitor C1 and the ground pin of the linear regulator U1 are connected to the power ground GND1. One end of the capacitor C2 is connected to the power ground GND1. The first output terminal of the linear regulator is connected to the other end of the capacitor C2, providing a 5V power supply.
9. A thermocouple signal analog circuit according to claim 3, characterized in that, The isolated 5V power supply 5V2 circuit includes a power isolation chip U2, a capacitor C3, and an inductor L1; one end of the capacitor C3 and one end of the inductor L1 are connected to the 5V1 power supply; the other end of the capacitor C3, the first pin VIN- of the power isolation chip U2, and the power ground GND1 are connected; the other end of the inductor L1 is connected to the second pin VIN+ of the power isolation chip U2; the fifth pin VOUT+ of the power isolation chip U2 provides the isolated power supply 5V2; and the fourth pin VOUT- of the power isolation chip U2 provides the isolated power ground GND2.
10. A thermocouple signal analog circuit according to claim 3, characterized in that, The 5V power supply 5V1 inverting circuit includes a voltage converter chip U3, polarized capacitors C4, C5, and C6. The first pin (BOOST), the eighth pin (V+), and the positive terminal of polarized capacitor C6 of the voltage converter chip U3 are connected to the 5V1 power supply. The negative terminal of polarized capacitor C6, the third pin (GND), and the positive terminal of polarized capacitor C5 are connected to the power ground (GND1). The second pin (CAP+) of the voltage converter chip U3 is connected to the positive terminal of polarized capacitor C4. The negative terminal of polarized capacitor C4 is connected to the fourth pin (CAP-) of the voltage converter chip U3. The fifth pin (VOUT) of the voltage converter chip U3 is connected to the negative terminal of polarized capacitor C5, providing a negative power supply -5V1.
11. A thermocouple signal analog circuit according to claim 3, characterized in that, The 5V power supply 5V2 inverting circuit includes a voltage converter chip U4, polarized capacitors C7, C8, and C9. The first pin (BOOST), the eighth pin (V+), and the positive terminal of polarized capacitor C9 are connected to the 5V2 power supply. The negative terminal of polarized capacitor C9, the third pin (GND), and the positive terminal of polarized capacitor C8 are connected to the power ground (GND2). The second pin (CAP+) of voltage converter chip U4 is connected to the positive terminal of polarized capacitor C7. The negative terminal of polarized capacitor C7 is connected to the fourth pin (CAP-) of voltage converter chip U4. The fifth pin (VOUT) of voltage converter chip U4 is connected to the negative terminal of polarized capacitor C8, providing a negative power supply -5V2.
12. A thermocouple signal analog circuit according to claim 3, characterized in that, The 1.5V voltage regulator circuit includes a voltage reference chip U6, resistors R1, R2, and R3. The first pin (R pin) and the third pin (K pin) of the voltage reference chip U6 are connected to one end of resistor R2 and one end of resistor R1. The second pin (A pin) of the voltage reference chip U6 is connected to power ground GND1. The other end of resistor R1 is connected to a 5V power supply. The other end of resistor R2 is connected to one end of resistor R3. The other end of resistor R3 is connected to power ground GND1. Resistors R2 and R3 form a voltage divider circuit, providing a stable 1.5V voltage signal at the connection point of resistors R2 and R3.