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CN-224216182-U - Isolated thermal resistance temperature signal conditioning system

CN224216182UCN 224216182 UCN224216182 UCN 224216182UCN-224216182-U

Abstract

The utility model belongs to the technical field of industrial automation measurement and control, and discloses an isolated thermal resistance temperature signal conditioning system. The utility model adopts an instrument amplifier with high common mode rejection ratio to reject common mode noise, optimizes hardware filtering design, adopts multistage low-pass filtering to eliminate power frequency harmonic waves, adopts a mirror image constant current source to enhance stability, adopts a double TVS diode clamping mode to add a reverse protection circuit, properly selects a power supply chip with a wide input voltage range, adopts VF/FV conversion time sequence control, adopts a scheme of dynamically adjusting cut-off frequency, automatically switches filtering parameters according to signal variable rate, and balances noise rejection and response speed.

Inventors

  • ZHANG LILI
  • CHEN MUXIA

Assignees

  • 北京合众恒跃科技有限公司

Dates

Publication Date
20260508
Application Date
20250528

Claims (10)

  1. 1. An isolated thermal resistance temperature signal conditioning system, comprising: The constant current source circuit is used for providing constant current for the thermal resistance temperature sensor and providing a constant current source for the VF conversion circuit; the amplifying circuit is used for proportionally amplifying the voltages at two ends of the thermal resistance temperature sensor and transmitting the amplified voltages to the VF conversion circuit; the VF conversion circuit is used for mapping the analog voltage into a frequency signal through a closed loop mechanism of integration, comparison and reset; the FV conversion circuit is used for mapping the frequency signal back to an analog voltage through a chained process of frequency, pulse width and voltage; the low-pass filter circuit is used for improving the stability of the analog voltage output by the FV conversion circuit by utilizing the low-pass filter; The linearization circuit is used for linearizing the voltage finally output in a resistance adjusting mode; The constant current source circuit, the amplifying circuit, the VF converting circuit, the FV converting circuit, the low-pass filter circuit and the linearization circuit are sequentially connected.
  2. 2. The isolated thermal resistor temperature signal conditioning system according to claim 1, wherein the constant current source circuit comprises a diode D3, a triode Q17, a resistor R36, a resistor R67, a diode D10, a triode Q26 and a resistor R37; One end of the resistor R37 is connected to the first end of the triode Q26, the second end of the triode Q26 is connected to the second end of the triode Q17, the third end of the triode Q17 is connected to the negative electrode of the diode D3, the first end of the triode Q17 is connected to one end of the resistor R36, the third end of the triode Q26 is connected to the negative electrode of the diode D10, and a resistor R67 is further disposed on one side of the diode D10.
  3. 3. The isolated thermal resistance temperature signal conditioning system according to claim 1, wherein the amplifying circuit comprises a resistor R38, a resistor R39, a resistor R40, an amplifier U4A, a resistor R36, a resistor R68, a resistor R66 and an amplifier U4B; The first end of the amplifier U4A is sequentially connected with one end of the resistor R39 and one end of the resistor R40, the other end of the resistor R39 is connected with one end of the resistor R38, the other end of the resistor R38 is sequentially connected with the third end of the amplifier U4A and one end of the resistor R69, the other end of the resistor R69 is sequentially connected with the first end of the amplifier U4B and one end of the resistor R68, the other end of the resistor R68 is connected with one end of the resistor R66, and the other end of the resistor R66 is connected with the third end of the amplifier U4B.
  4. 4. The isolated thermal resistance temperature signal conditioning system of claim 1, wherein the amplifying circuit further comprises a dual TVS tube structure protection circuit comprising a capacitor C23 and a diode Q22, the diode C23 being connected in parallel with the first and second ends of the diode Q22.
  5. 5. The isolated thermal resistor temperature signal conditioning system according to claim 1, wherein the VF conversion circuit comprises a switch tube Q13, a switch tube Q14, a capacitor C12, an amplifier U5A, a resistor R30, a resistor R29, a resistor R26, a capacitor C10, a resistor R24, a resistor R25, a capacitor C14, a resistor R35, a resistor R41, a chip U1 and a capacitor C11; The second end of the switch tube Q13 is sequentially connected with one end of the capacitor C12 and the second end of the amplifier U5A, the other end of the capacitor C12 is sequentially connected with the first end of the amplifier U5A, the second end of the amplifier Q14, one end of the capacitor C10 and one end of the resistor R24, the other end of the capacitor C10 is sequentially connected with the other end of the resistor R24, the resistor R25 and the first end of the chip U1, and the C1 end of the chip U1 is connected with the capacitor C11; The second end of the chip U1 is connected with one end of the resistor R26, the other end of the resistor R26 is sequentially connected with one end of the resistor R30, one end of the resistor R29 and the first end of the switch tube Q13, the other end of the resistor R30 is connected with the third end of the amplifier U5A, the third end of the switch tube Q13 is connected with the third end of the switch tube Q14, the first end of the switch tube Q14 is sequentially connected with one end of the capacitor C14, one end of the resistor R35 and one end of the resistor R41, and the other end of the resistor R35 is connected with the other end of the capacitor C14.
  6. 6. The isolated thermal resistor temperature signal conditioning system of claim 1, wherein the FV switching circuit comprises a chip U2, a resistor R17, a capacitor C8, a capacitor C9, a diode Q4, a resistor R15, a resistor R54, a resistor R22, a resistor R58, a resistor R21, a resistor R20, a transistor Q8, a resistor R61, a resistor R56, a capacitor C21, an amplifier U6A, and a transistor Q11; The end A2 of the chip U2 is connected with one end of the resistor R17, the other end of the resistor R17 is sequentially connected with one end of the capacitor C9 and the ends A1 and B2 of the chip U2, the end C1 of the chip U2 is connected with one end of the capacitor C8, and the other end of the capacitor C8 is connected with the other end of the capacitor C9; The first end of the triode Q8 is sequentially connected with the resistor R21, the resistor R20 and the resistor R58, the second end of the triode Q8 is sequentially connected with the second end of the amplifier U6A, one end of the capacitor C21, one end of the resistor R61 and one end of the resistor R22, the other end of the resistor R22 is connected with one end of the resistor R54, and the other end of the resistor R54 is sequentially connected with the resistor R15 and the diode Q4; The other end of the resistor R61 is connected with one end of the resistor R56, the other end of the resistor R56 is sequentially connected with the other end of the capacitor C21, the second end of the triode Q11 and the first end of the amplifier U6A, and the third end of the triode Q11 is connected with the third end of the triode Q8.
  7. 7. An isolated thermal resistance temperature signal conditioning system according to claim 1, wherein the chain process of passing frequency, pulse width and voltage, mapping the frequency signal back to an analog voltage comprises: Isolating an output signal of the VF conversion circuit by using a photoelectric coupler, and shaping the output signal of the photoelectric coupler into a square wave signal with the same frequency as the-F conversion circuit and a fixed width by using a pulse shaping circuit; When the input voltage is at a low level, the triode Q8 is cut off, and the input signal of the proportional amplifying circuit U6A is a reference voltage; when the input voltage is at a high level, the triode Q8 is conducted, and the reference voltage and the constant current source act on the proportional amplifying circuit U6A at the same time; based on kirchhoff theorem, calculating a theoretical value of output voltage, and obtaining a linear relation between the output voltage of the FV circuit and the RTD resistance by means of the relation between the frequency of the input voltage and the resistance of the thermal resistance temperature sensor.
  8. 8. The isolated thermal resistance temperature signal conditioning system according to claim 1, wherein the low pass filter circuit comprises a capacitor C6, a resistor R5, a resistor R7, a resistor R55, a resistor R11, a capacitor C5, an amplifier U1B, a resistor R9, a capacitor C4 and a resistor R14; The third end of the amplifier U1B is sequentially connected with the capacitor C4 and one end of the resistor R9, and the other end of the resistor R9 is connected with one end of the capacitor C6; The second end of the amplifier U1B is sequentially connected with one end of the capacitor C5 and the third end of the resistor R55, the second end of the resistor R55 is sequentially connected with the resistor R11 and one end of the resistor R7, the other end of the resistor R7 is sequentially connected with the first end of the resistor R55 and one end of the resistor R5, the other end of the resistor R5 is sequentially connected with the other end of the capacitor C6 and one end of the resistor R14, and the other end of the resistor R14 is sequentially connected with the other end of the capacitor C5 and the first end of the amplifier U1B.
  9. 9. The isolated thermal resistor temperature signal conditioning system of claim 1, wherein the linearization circuit comprises an amplifier U1A, a resistor R8, a resistor R6, a capacitor C2, a voltage reference chip Q1, a triode Q18, a resistor R44, a resistor R1, a resistor R45, a triode Q19, a resistor R46, a triode Q2, a resistor R3, a resistor R48, a resistor R50, a triode Q3, a resistor R49, a triode Q20, a triode Q21, a triode R52 and a triode R51; The first end of the triode Q21 is sequentially connected with the third end of the triode Q21, the resistor R52 and one end of the resistor R51, the other end of the resistor R51 is sequentially connected with one end of the resistor R48 and one end of the resistor R20, the second end of the triode Q20 is sequentially connected with one end of the resistor R49, the other end of the resistor R49 is sequentially connected with one end of the resistor R50, one end of the resistor R46, one end of the resistor R45, the second end of the amplifier U1A and one end of the capacitor C1, the other end of the resistor R50 is connected with the second end of the triode Q3, the first end of the triode Q3 is sequentially connected with the other end of the resistor R48 and one end of the resistor R3, the other end of the resistor R3 is sequentially connected with the first end of the triode Q2 and one end of the resistor R1, and the second end of the resistor Q2 is connected with the other end of the resistor R46; The other end of the resistor R45 is connected with the second end of the triode Q19, the first end of the triode Q19 is sequentially connected with the other end of the resistor R1 and one end of the resistor R44, the other end of the resistor R44 is connected with the first end and the third end of the triode Q18, and the second end of the triode Q18 is connected with the first end of the voltage reference chip Q1; The third end of the amplifier U1A is connected with the resistor R8, the other end of the capacitor C1 is connected with the first end of the amplifier U1A, one end of the resistor R6 and one end of the capacitor C2, and the other end of the resistor R6 is connected with the other end of the capacitor C2.
  10. 10. An isolated thermal resistance temperature signal conditioning system according to claim 9, wherein linearizing the final output voltage by adjusting the resistance comprises: The resistance inside the linearization circuit is regulated by controlling the conduction states of the triode Q20, the triode Q3, the triode Q2 and the triode Q19, so that linearization regulation of the final output voltage is realized.

Description

Isolated thermal resistance temperature signal conditioning system Technical Field The invention relates to the technical field of industrial automation measurement and control, in particular to an isolated thermal resistance temperature signal conditioning system. Background RTD (thermal resistance temperature sensor) shows high accuracy and high reliability in the field of temperature measurement by virtue of excellent temperature sensitivity and chemical stability of platinum (Pt) materials, and the RTD (thermal resistance temperature sensor) typically represents that Pt100 (resistance value 100 omega at 0 ℃) and Pt1000 (resistance value 1000 omega at 0 ℃) can stably work in a wide temperature range from-200 ℃ to +850 ℃ so as to meet extreme environmental requirements such as ultralow temperature experiments, high temperature industrial furnace monitoring and the like. The resistance-temperature (R-T) relation of the platinum resistor is nearly linear, after nonlinear deviation is corrected by combining CALLENDAR-Van Dusen equation (a formula for calculating the relation between temperature and resistance), the measurement error can be controlled within +/-0.1 ℃, part of high-precision models can reach +/-0.03 ℃, and the long-term stability is outstanding. In industrial application, RTD is widely used in process control scenes such as chemical industry reation kettle temperature monitoring, electric steam pipeline thermal management, metallurgical motor overheat protection, etc. and is also the core sensing element in laboratory constant temperature tank, medical equipment and new energy field (such as lithium cell production, hydrogen energy storage tank low temperature monitoring). The RTD is designed to adapt to complex industrial environment by adopting a multi-wire interface, namely 2 wires are low in cost and limited in precision, the RTD is suitable for short-distance scenes, 3 wires become an industrial mainstream scheme by compensating wire resistance (for example, 100 meters of cable error can be reduced to +/-0.1 ℃), and 4 wires are used for isolating excitation and measurement paths based on Kelvin connection, so that +/-0.01 ℃ ultra-high precision is realized, and the RTD is mainly used for laboratory calibration. In addition, the differential signal transmission and shielding twisted pair design effectively inhibits common mode noise caused by starting and stopping of a motor, and the like, so that the anti-interference capability of an industrial field is further ensured. Defects in the prior art: 1. the power frequency interference suppression is insufficient: the problem is that 50/60Hz power frequency noise is superimposed on the weak RTD signal, resulting in ADC output jump (e.g. + -0.5 ℃ fluctuation). The root is that (1) the Common Mode Rejection Ratio (CMRR) of the differential amplifier is not enough (< 80 dB), and common mode noise cannot be effectively eliminated. (2) The filter circuit is designed coarsely (such as the single-stage RC filter cutoff frequency is too high) and is not optimized for power frequency harmonic waves. (3) Ground design imperfections (e.g., ground loops) or the lack of shielded cables introduce spatial electromagnetic interference. 2. Lack of power misconnection protects fragile equipment: the problem is that the front-end circuit is burnt out due to reverse connection or overvoltage (such as 48V for 24V misconnection) of the power supply, and the equipment failure rate is high. The source is (1) to reduce the cost, omit reverse protection diode, TVS tube or self-recovery fuse (PTC). (2) Depending on the withstand voltage limit of the linear voltage stabilizing chip (such as LM 7805), no redundancy protection is designed. 3. The multi-stage filtering results in signal delay: The problem is that the response time of the system is too long (such as >200 ms) when the temperature is changed in a step mode, and the real-time control requirement cannot be met. The method is based on (1) superposition digital filtering (moving average) by adopting multistage analog filtering (such as RC low pass and operational amplifier buffering), and accumulating phase delay. (2) The filtering cut-off frequency is too low (e.g., 10 Hz) to sacrifice bandwidth, and the dynamic response contradicts noise suppression. In general, the shortcomings of the prior art are: (1) Insufficient power frequency interference suppression. The method is characterized in that 50/60Hz power frequency noise is superimposed on a weak RTD signal, so that the ADC output jumps (such as + -0.5 ℃ fluctuation). (2) The problem of equipment damage caused by the lack of power supply misconnection protection. The method is characterized in that the front-end circuit is burnt out due to reverse connection or overvoltage (for example, 24V misconnection is 48V) of the power supply, and the equipment failure rate is high. (3) The multi-stage filtering causes signal delay problems. The method is characterized