Four-wire temperature acquisition and self-checking circuit

Abstract

The application provides a four-wire temperature acquisition and self-checking circuit, which comprises a constant current source generation circuit, a constant current source detection circuit, a first operational amplifier conditioning circuit, a second operational amplifier conditioning circuit, a four-wire temperature acquisition unit and an ADC data conversion and communication control unit; the ADC data conversion and communication control unit comprises an ADC conversion chip A3 for outputting and inputting a reference voltage VREF; the constant current I_TEMP output by the constant current source generation circuit flows through the sampling resistor R10 and the four-wire temperature acquisition unit, and the voltage generated across the sampling resistor R10 is input to the constant current source detection circuit to output the voltage TEMP_V to the ADC conversion chip A3; when the I_TEMP flows through the four-wire temperature measuring element RT in the four-wire temperature acquisition unit, the voltage generated across the four-wire temperature measuring element RT is input to the first operational amplifier conditioning circuit and the second operational amplifier conditioning circuit respectively, and then the stable voltages TEMP_VA and TEMP_VB are output to the ADC conversion chip A3 respectively. The application can improve the temperature measuring precision and the accuracy of detecting the voltages of the circuits, and ensure the normal operation of the system in the case of one-side fault.

Description

Technical Field

[0001] This invention belongs to the field of temperature acquisition technology in energy storage battery management systems, specifically relating to a four-wire temperature acquisition and self-calibration circuit. Background Technology

[0002] In existing energy storage battery management systems, temperature acquisition typically employs a four-wire system, with two wires connected to each end of the resistance temperature detector (RTD). Two of these wires provide a constant current to the RTD, converting the resistance R into a voltage signal U. The other two wires then lead out U and connect it to the control unit to obtain temperature data. This four-wire temperature measurement completely eliminates the resistance effect of the RTD leads.

[0003] However, the existing four-wire temperature acquisition technology has certain limitations. It cannot achieve long-distance temperature data transmission; and it does not take into account the verification of the constant current source and the redundancy of the temperature detection circuit, so it cannot achieve accurate temperature data measurement. Once a fault occurs, the system cannot work properly, affecting work efficiency. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a four-wire temperature acquisition and self-calibration circuit, which can improve temperature measurement accuracy, enhance circuit self-calibration to ensure the accuracy of temperature acquisition data, and enable long-distance temperature data transmission.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A four-wire temperature acquisition and self-calibration circuit includes a constant current source generation circuit, a constant current source detection circuit, a first operational amplifier conditioning circuit, a second operational amplifier conditioning circuit, a four-wire temperature acquisition unit, and an ADC data conversion and communication control unit. The ADC data conversion and communication control unit includes an ADC conversion chip A3 that outputs and inputs a reference voltage VREF. The reference voltage VREF is fed by the constant current source generation circuit to output a constant current I_TEMP. The constant current I_TEMP flows through a sampling resistor R10 and the four-wire temperature acquisition unit. A voltage is generated across the sampling resistor R10 and input to the constant current source detection circuit, which outputs a voltage TEMP_V to the ADC data conversion and communication control unit. The four-wire temperature acquisition unit includes a four-wire temperature sensing element RT. When the constant current I_TEMP flows through the four-wire temperature sensing element RT, the voltage generated across the four-wire temperature sensing element RT is input to the first operational amplifier conditioning circuit and the second operational amplifier conditioning circuit, respectively. The first and second operational amplifier conditioning circuits output stable voltages TEMP_VA and TEMP_VB to the ADC data conversion and communication control unit, respectively.

[0007] Furthermore, the ADC data conversion and communication control unit also includes an MCU unit that communicates with the ADC conversion chip A3. The voltage value of the temperature is obtained through the ADC's built-in communication method and transmitted to the MCU control unit, which is beneficial for long-distance temperature data transmission.

[0008] Furthermore, the reference voltage VREF, voltage TEMP_V, and stable voltages TEMP_VA and TEMP_VB are input to the acquisition channel of the ADC conversion chip A3 and interact with the MCU control unit via a communication connection. When the four voltages VREF, TEMP_V, TEMP_VA, and TEMP_VB are input to the ADC conversion chip A3 in the ADC data conversion and communication control unit, they are converted into communication signals, which are then acquired by the MCU control unit to calculate the actual temperature value.

[0009] Furthermore, the communication connection includes SPI communication. SPI is only one communication method; other communication methods can also be selected, such as voltage acquisition chips with I2C or other communication methods, which can expand the functionality beyond just temperature data acquisition.

[0010] Furthermore, the four-wire temperature acquisition unit also includes a TVS diode V2 to prevent the voltage across the four-wire temperature sensing element RT from exceeding the limit, and TVS diodes V1 and V3 to prevent the voltage between the temperature sensing element RT and ground from exceeding the limit. When I_TEMP flows through the temperature sensing element RT in the four-wire temperature acquisition unit, the voltage across RT is prevented from exceeding the limit by TVS diode V2, and the voltage between RT and ground is prevented from exceeding the limit by TVS diodes V1 and V3 respectively, so as to avoid damage to the subsequent circuitry.

[0011] Furthermore, the constant current source generation circuit includes an operational amplifier conditioning circuit composed of operational amplifier A1B. The reference voltage VREF in the constant current source generation circuit is generated by ADC chip A3. After being conditioned by the operational amplifier conditioning circuit composed of A1B, the reference voltage VREF outputs a constant current I_TEMP, which flows through the sampling resistor R10 and the temperature sensing element RT.

[0012] Furthermore, the constant current source detection circuit includes a filter circuit and an operational amplifier conditioning circuit composed of operational amplifiers A2B. The voltage generated across the sampling resistor R10 enters the constant current source detection circuit, which can filter out most high-frequency noise and output a stable voltage TEMP_V. When the output current of the constant current source generating circuit remains constant, TEMP_V also remains constant. If the TEMP_V voltage value detected by the ADC is accurate, it is determined that the current source output is normal and the constant current source detection circuit is working properly. If TEMP_V changes, it can be determined that there is a fault in the current source or the constant current source detection circuit, and it should be repaired immediately.

[0013] Furthermore, the first and second op-amp conditioning circuits share the same circuit structure and electrical parameters, including both op-amp conditioning and filtering circuits. Redundancy is used to ensure the accuracy of the voltage across the temperature sensing element. Even if one op-amp conditioning circuit fails, the other can still transmit temperature data normally, guaranteeing normal system operation. When TEMP_V remains constant, the voltage values ​​of TEMP_VA and TEMP_VB output by the first and second op-amp conditioning circuits, after being detected by the ADC, are the same, indicating a valid temperature measurement. If the voltage values ​​of TEMP_VA and TEMP_VB are different or significantly different, the temperature measurement is invalid. The correct data should be selected for calculation based on the actual situation, and the damaged component must be repaired immediately.

[0014] Furthermore, filter components are added to the constant current source detection circuit, the first op-amp conditioning circuit, and the subsequent stages of the second op-amp conditioning circuit. The addition of filter component C4 to the subsequent stage of the constant current source detection circuit results in a smoother waveform of the input ADC voltage TEMP_V, leading to better performance. Similarly, the addition of filter components C9 and C16 to the subsequent stages of the first and second op-amp conditioning circuits further smooths the waveforms of the input ADC voltages TEMP_VA and TEMP_VB, resulting in even better performance.

[0015] Compared with existing technologies, the advantages of this invention are:

[0016] 1. The present invention provides a four-wire temperature acquisition and self-calibration circuit that can completely eliminate the influence of line resistance on temperature measurement accuracy by using a four-wire temperature sensing element; and through redundant design, it detects the accuracy of the voltage across the temperature sensing element, and even if one side of the operational amplifier conditioning circuit is found to be faulty, it can still transmit temperature data normally through the other side of the operational amplifier conditioning circuit, ensuring normal system operation.

[0017] 2. By using an ADC converter chip to both output and input a reference voltage, the accuracy of the reference voltage is verified to ensure the accuracy of the subsequent constant current source;

[0018] 3. By adding a sampling resistor, the constant current source current value is captured, and after filtering and conditioning, it is output to the ADC, which can increase the monitoring of the constant current source and the detection of its accuracy.

[0019] 4. The voltage value of temperature is obtained through the ADC's built-in SPI communication and transmitted to the MCU control unit, which is beneficial for long-distance temperature data transmission;

[0020] 5. The overall system circuit of this invention can be fabricated as a modular circuit, with a reserved SPI communication interface, which can interact with a control system with SPI communication, thus facilitating the functional expansion and widespread application of the module.

[0021] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0022] Figure 1 This is a circuit diagram of the four-wire temperature acquisition and self-calibration circuit of the present invention;

[0023] In the figure, there is a constant current source generating circuit 1, a constant current source detection circuit 2, a first operational amplifier conditioning circuit 3, a second operational amplifier conditioning circuit 4, a four-wire temperature acquisition unit 5, and an ADC data conversion and communication control unit 6. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0025] like Figure 1 As shown, a four-wire temperature acquisition and self-calibration circuit mainly includes six sub-circuit units: a constant current source generation circuit 1, a constant current source detection circuit 2, a first operational amplifier conditioning circuit 3, a second operational amplifier conditioning circuit 4, a four-wire temperature acquisition unit 5, and an ADC data conversion and communication control unit 6. Each circuit unit calibrates and monitors each other to ensure the accuracy of the acquired temperature data. The ADC data conversion and communication control unit 6 includes an ADC conversion chip A3 that outputs and inputs a reference voltage VREF. The reference voltage VREF outputs a constant current I_TEMP through a constant current source generation circuit 1. The constant current I_TEMP flows through a sampling resistor R10 and a four-wire temperature acquisition unit 5. At this time, a voltage is generated across the sampling resistor R10 and enters the constant current source detection circuit 2 to output a voltage TEMP_V to the ADC data conversion and communication control unit 6. The four-wire temperature acquisition unit 5 includes a four-wire temperature sensing element RT. When the constant current I_TEMP flows through the four-wire temperature sensing element RT, the voltage generated across the four-wire temperature sensing element RT is input to the first operational amplifier conditioning circuit 3 and the second operational amplifier conditioning circuit 4, respectively. The first operational amplifier conditioning circuit 3 and the second operational amplifier conditioning circuit 4 output stable voltages TEMP_VA and TEMP_VB to the ADC data conversion and communication control unit 6, respectively.

[0026] In this embodiment, the reference voltage VREF in the constant current source generation circuit 1 is generated by the ADC chip A3. After the reference voltage VREF is conditioned by the operational amplifier A1B, the output current is I_TEMP. According to the principle of virtual short and virtual open,

[0027]

[0028] In this embodiment, R1 = R8 = 49.9KΩ, R2 = R9 = 10KΩ, R3 = R4 = 100Ω, all with a resistor accuracy of 0.1%, VREF = 2.5V, and the op-amp A1B is OP2177, so I_TEMP is approximately 5.06mA.

[0029] In this embodiment, the constant current source flows through the sampling resistor R10 and the four-wire temperature sensing element RT.

[0030] When I_TEMP flows through the sampling resistor R10, a voltage will be generated across the resistor. This voltage will enter the constant current source detection circuit 2, which is composed of a filter circuit and an operational amplifier A2B conditioning circuit. The output voltage at this time is TEMP_V. According to the principle of virtual short and virtual open circuits,

[0031]

[0032] In this embodiment, R10 = 499Ω, R5 = R6 = R12 = R13 = 200KΩ, R7 = R14 = 1MΩ, and the resistance accuracy is 0.1%. The op-amp A2B is OP2177, so TEMP_V = 6.312V.

[0033] Where C3 = 47nF, the EMI filtering coefficient of this circuit is:

[0034]

[0035] The filter circuit in constant current source detection circuit 2 can filter out most high-frequency noise. An additional filter element C4 is added in the subsequent stage, resulting in a smoother waveform for the input ADC voltage TEMP_V and improved performance.

[0036] When I_TEMP flows through the four-wire temperature sensing element RT in the four-wire temperature acquisition unit 5, the voltage generated across the four-wire temperature sensing element RT is prevented from exceeding the limit by TVS tube V2, and the voltage generated between the two ends of RT and ground is prevented from exceeding the limit by TVS tubes V1 and V3 respectively, so as to avoid damaging the subsequent circuit.

[0037] In this embodiment, V1 and V3 are both SMBJ11CA, and V2 is SMBJ16CA, meaning the voltage limit across the temperature sensing element RT is 16V, and the voltage limit to ground is 11V. The TVS diode can be configured according to specific needs.

[0038] After a constant current I_TEMP flows into the two ends of the temperature sensing element RT, the resulting voltage is applied to the two ends of the first operational amplifier conditioning circuit 3 and the second operational amplifier conditioning circuit 4, respectively. After conditioning, stable voltages TEMP_VA and TEMP_VB are output respectively.

[0039] According to the principle of virtual shortness and virtual breakage, it can be known that

[0040]

[0041]

[0042] In this embodiment, R15 = R16 = R19 = R20 = 100KΩ, R17 = R21 = 1MΩ, and the resistor accuracy is 0.1%. C5 = C8 = 1nF, C7 = 100nF, and the op-amp A1C is OP2177. Therefore, TEMP_VA = RT * 5.06mA * 5 = 0.0253 * RT.

[0043] In this embodiment, the components of the first op-amp conditioning circuit 3 and the second op-amp conditioning circuit 4 are identical, their electrical parameters are completely the same, and their circuit structures are completely identical. Therefore, TEMP_VB = RT * 5.06mA * 5 = 0.0253 * RT.

[0044] The EMI coefficients of the first op-amp conditioning circuit 3 and the second op-amp conditioning circuit 4 are:

[0045]

[0046] The filter circuits of the first op-amp conditioning circuit 3 and the second op-amp conditioning circuit 4 can filter out most of the high-frequency noise. Further filter components C9 and C16 are added in the subsequent stages to make the waveforms of the input ADC voltages TEMP_VA and TEMP_VB smoother and more effective.

[0047] When the four voltages—reference voltage VREF, voltage TEMP_V, stable voltage TEMP_VA, and TEMP_VB—are input to the ADC conversion chip A3 in the ADC data conversion and communication control unit 6, they are converted into communication signals, which are then acquired by the MCU control unit to calculate the actual temperature value. This embodiment uses SPI communication signals. SPI is only one communication method; other communication methods can also be selected, such as voltage acquisition chips with I2C or other communication methods, expanding the functionality beyond just temperature data acquisition.

[0048] The ADC converter chip A3 is an AD7324BRUZ, a 12-bit ADC. Controlled by the MCU, pin 5 of the ADC converter chip A3 can output a reference voltage VREF, which is then fed into the constant current source generation circuit 1 to generate a constant current source, forming a closed-loop detection circuit.

[0049] All four voltage inputs are fed into the ADC acquisition channel, and data interaction with control units such as MCUs is achieved through SPI communication. This enables long-distance temperature data transmission to a large extent and can be made into a temperature measurement module. Functional expansion can be achieved by connecting to the communication interface.

[0050] The self-calibration method of the four-wire temperature acquisition and self-calibration circuit of this invention is as follows:

[0051] 1. The reference voltage VREF serves as both the ADC output and input, enabling voltage accuracy determination and cross-calibration with the voltage TEMP_V: When VREF is constant, if the VREF voltage value detected by the ADC is accurate, then the ADC is considered to be working normally.

[0052] 2. At this time, the current output of constant current source generating circuit 1 should be constant, so the voltage TEMP_V should be constant. If the voltage value of TEMP_V detected by ADC is accurate, then it is determined that the current source output is normal and the constant current source detection circuit 2 is working normally.

[0053] If the voltage TEMP_V changes, it can be determined that there is a fault in the current source or the constant current source detection circuit 2, and it should be repaired immediately.

[0054] 3. The stable voltages TEMP_VA and TEMP_VB are designed to be redundant and can mutually correct the data: When TEMP_V is constant, the voltage values ​​of TEMP_VA and TEMP_VB output by op-amp conditioning circuit 3 and op-amp conditioning circuit 4 are the same after being detected by ADC, then the temperature measurement is determined to be valid.

[0055] If the TEMP_VA and TEMP_VB voltage values ​​are different or significantly different, the temperature measurement is invalid. The correct data should be selected for calculation based on the actual situation, and the damaged component should be repaired immediately.

[0056] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A four-wire temperature acquisition and self-calibration circuit, characterized in that, It includes a constant current source generating circuit (1), a constant current source detection circuit (2), a first operational amplifier conditioning circuit (3), a second operational amplifier conditioning circuit (4), a four-wire temperature acquisition unit (5), and an ADC data conversion and communication control unit (6); The ADC data conversion and communication control unit (6) includes an ADC conversion chip A3 that outputs and inputs a reference voltage VREF. The reference voltage VREF outputs a constant current I_TEMP through a constant current source generation circuit (1). The constant current I_TEMP flows through a sampling resistor R10 and a four-wire temperature acquisition unit (5). The voltage generated across the sampling resistor R10 enters the constant current source detection circuit (2) and outputs a voltage TEMP_V to the ADC data conversion and communication control unit (6). If the voltage TEMP_V remains unchanged, the current output is determined to be normal. If the voltage TEMP_V changes, the current source or the constant current source detection circuit (2) is determined to be faulty. The four-wire temperature acquisition unit (5) includes a four-wire temperature sensing element RT. The constant current I_TEMP flows through the four-wire temperature acquisition unit (5). The voltage generated at both ends of the four-wire temperature sensing element RT is input to the first operational amplifier conditioning circuit (3) and the second operational amplifier conditioning circuit (4). The first operational amplifier conditioning circuit (3) and the second operational amplifier conditioning circuit (4) output stable voltages TEMP_VA and TEMP_VB to the ADC data conversion and communication control unit (6), respectively. The ADC data conversion and communication control unit (6) also includes an MCU unit that is communicatively connected to the ADC conversion chip A3; The reference voltage VREF, voltage TEMP_V, stable voltage TEMP_VA, and TEMP_VB are input to the acquisition channel of the ADC conversion chip A3 and interact with the MCU control unit via a communication connection.

2. The four-wire temperature acquisition and self-calibration circuit according to claim 1, characterized in that, The communication connection includes SPI communication.

3. The four-wire temperature acquisition and self-calibration circuit according to claim 1, characterized in that, The four-wire temperature acquisition unit (5) also includes a TVS diode V2 to prevent the voltage across the four-wire temperature sensing element RT from exceeding the limit, and a TVS diode V1 and a TVS diode V3 to prevent the voltage between the two ends of the temperature sensing element RT and ground from exceeding the limit.

4. The four-wire temperature acquisition and self-calibration circuit according to claim 1, characterized in that, The constant current source generating circuit (1) includes an operational amplifier conditioning circuit composed of operational amplifier A1B.

5. The four-wire temperature acquisition and self-calibration circuit according to claim 1, characterized in that, The constant current source detection circuit (2) includes a filter circuit and an operational amplifier conditioning circuit composed of operational amplifier A2B.

6. The four-wire temperature acquisition and self-calibration circuit according to claim 1, characterized in that, The first op-amp conditioning circuit (3) and the second op-amp conditioning circuit (4) have the same circuit structure and electrical parameters, including op-amp conditioning circuit and filter circuit.

7. A four-wire temperature acquisition and self-calibration circuit according to claim 5 or 6, characterized in that, The constant current source detection circuit (2), the first operational amplifier conditioning circuit (3), and the second operational amplifier conditioning circuit (4) are respectively equipped with filter elements.

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