Thermal conductivity detection circuit based on double constant current source bridge

Abstract

The invention discloses a thermal conductivity detection circuit based on double constant current source bridges, which belongs to the technical field of thermal conductivity detection circuits and comprises a first hot wire resistance module, a second hot wire resistance module, a first current negative feedback regulation module, a second current negative feedback regulation module, a detection module, a current setting module and a microcontroller. The first hot wire resistance module is connected with the first current negative feedback adjusting module and is connected with the input end of the detection module, the second hot wire resistance module is connected with the second current negative feedback adjusting module and is connected with the input end of the detection module, and the current setting module is connected with the output end of the microcontroller. The detection module is connected with the input end of the microcontroller and is connected with the input end of the first current negative feedback adjusting module and the input end of the second current negative feedback adjusting module. Constant current control is achieved in a low-cost mode, the bridge can be balanced by adjusting the size of the two constant current sources, and the effect of bridge zero setting is achieved.

Description

Technical Field

[0001] This invention relates to the field of technology, and specifically to a thermal conductivity detection circuit based on a dual constant current source bridge. Background Technology

[0002] For a general four-wire bridge thermal conductivity detection circuit, the bridge zeroing circuit needs to be zeroed using a center-tapped three-terminal potentiometer or a programmable digital potentiometer, which makes the circuit design complex and costly.

[0003] The aforementioned problems urgently need to be solved. To address this, a thermal conductivity detection circuit based on a dual constant current source bridge is proposed. The circuit is simple and facilitates bridge zeroing. Summary of the Invention

[0004] The technical problem to be solved by this invention is: how to achieve constant current control and balance of the bridge by adjusting the magnitude of the two constant current sources in a low-cost manner, thereby achieving the effect of zeroing the bridge, and provides a thermal conductivity detection circuit based on a dual constant current source bridge.

[0005] The present invention solves the above-mentioned technical problems through the following technical solution: The present invention includes a first hot wire resistor module, a second hot wire resistor module, a first current negative feedback adjustment module, a second current negative feedback adjustment module, a detection module, a current setting module, and a microcontroller; the first hot wire resistor module is connected to the first current negative feedback adjustment module and is also connected to the input terminal of the detection module; the second hot wire resistor module is connected to the second current negative feedback adjustment module and is also connected to the input terminal of the detection module; the current setting module is connected to the output terminal of the microcontroller and to the input terminals of the first and second current negative feedback adjustment modules; the detection module is connected to the input terminal of the microcontroller.

[0006] Furthermore, the first hot wire resistor module includes hot wire resistors Rt1 and Rt2, which are connected in series and located in the thermal conductivity cell. The input terminal of the detection module is connected between the hot wire resistors Rt1 and Rt2.

[0007] Furthermore, the second hot wire resistor module includes hot wire resistors Rt3 and Rt4, which are connected in series and located in the thermal conductivity cell. The input terminal of the detection module is connected between the hot wire resistors Rt3 and Rt4.

[0008] Furthermore, the first current negative feedback regulation module includes transistors Q1 and Q2, operational amplifier U1, and current sampling resistor Rs1. The non-inverting input terminal of operational amplifier U1 is connected in series with resistor R2 and then connected to one end of current sampling resistor Rs1, and simultaneously connected to one end of hot wire resistor Rt2. The other end of hot wire resistor Rt2 is connected to one end of hot wire resistor Rt1. The other end of current sampling resistor Rs1 is connected to GND_ISO isolation ground. The other end of hot wire resistor Rt1 is connected to the emitter of transistor Q2. Transistor Q... The collector of transistor Q2 is connected to the high-voltage power supply VH. The base of transistor Q2 is connected to the collector of transistor Q1. The base of transistor Q1 is connected in series with resistor R4 and then connected to the output of operational amplifier U1. The emitter of transistor Q1 is connected to GND_ISO for isolation. The inverting input of operational amplifier U1 is connected to the output of the current setting module. Resistor R3 is connected in parallel to the output and inverting input of operational amplifier U1. Capacitor C1 is connected in parallel with resistor R3. The negative power supply input of operational amplifier U1 is connected to GND_ISO for isolation.

[0009] Furthermore, the first current negative feedback regulation module includes transistors Q3 and Q4, operational amplifier U2, and current sampling resistor Rs2. The non-inverting input terminal of operational amplifier U2 is connected in series with resistor R7 and then connected to one end of current sampling resistor Rs2, and simultaneously connected to one end of hot wire resistor Rt4. The other end of hot wire resistor Rt4 is connected to one end of hot wire resistor Rt3. The other end of current sampling resistor Rs2 is connected to GND_ISO isolation ground. The other end of hot wire resistor Rt3 is connected to the emitter of transistor Q4. Transistor Q... The collector of transistor Q4 is connected to the high-voltage power supply VH. The base of transistor Q4 is connected to the collector of transistor Q3. The base of transistor Q3 is connected in series with resistor R9 and then connected to the output of operational amplifier U2. The emitter of transistor Q3 is connected to GND_ISO for isolation. The inverting input of operational amplifier U2 is connected to the output of the current setting module. Resistor R8 is connected in parallel to the output and inverting input of operational amplifier U2. Capacitor C2 is connected in parallel with resistor R8. The negative power supply input of operational amplifier U2 is connected to GND_ISO for isolation.

[0010] Furthermore, the current setting module includes digital-to-analog converter chips DAC1 and DAC2; the input terminal of digital-to-analog converter chip DAC1 is connected to the microcontroller MCU through an electrical isolation device U4, and the output terminal is connected to the inverting input terminal of operational amplifier U1; the input terminal of digital-to-analog converter chip DAC2 is connected to the microcontroller MCU through an electrical isolation device U4, and the output terminal is connected to the inverting input terminal of operational amplifier U2.

[0011] Furthermore, the detection module includes a differential amplifier U3 and an analog-to-digital converter (ADC) chip. The inverting input terminal of the differential amplifier U3 is connected between hot wire resistors Rt1 and Rt2 and connected to GND. The non-inverting input terminal of the differential amplifier U3 is connected between hot wire resistors Rt3 and Rt4. The output terminal of the differential amplifier U3 is connected to the input terminal of the ADC chip. The output terminal of the ADC chip is connected to the input terminal of the microcontroller (MCU). The negative power supply input terminal of the differential amplifier U3 is connected to GND.

[0012] Furthermore, the thermal conductivity detection circuit based on the dual constant current source bridge also includes bias resistors R5 and R10, which are connected in parallel between the collector and base of transistor Q2, and resistor R10 is connected in parallel between the collector and base of transistor Q4.

[0013] Furthermore, the current sampling resistors Rs1 and Rs2 are both precision resistors with equal resistance values.

[0014] Furthermore, when zeroing the thermal conductivity detection circuit based on the dual constant current source bridge, the magnitudes of the current Irs1 on the current sampling resistor Rs1 and the current Irs2 on the current sampling resistor Rs2 are adjusted so that the output voltage of the differential amplifier U3 is close to 0V, which is considered as the zeroing is complete.

[0015] Compared with the prior art, the present invention has the following advantages: the thermal conductivity detection circuit based on the dual constant current source bridge achieves constant current control in a low-cost manner, and the bridge can be balanced by adjusting the magnitude of the two constant current sources, thus achieving the effect of zeroing the bridge. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the thermal conductivity detection circuit of the dual constant current source bridge in an embodiment of the present invention, wherein the differential amplifier circuit is a differential amplifier. Detailed Implementation

[0017] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0018] like Figure 1 As shown, this embodiment provides a technical solution: a thermal conductivity detection circuit for a dual constant current source bridge, which allows the bridge to achieve zero-adjustment by adjusting the magnitude of the two constant current sources.

[0019] The thermal conductivity detection circuit of the dual constant current source bridge includes operational amplifiers U1 and U2, transistors Q1 to Q4, digital-to-analog converter chips DAC1 and DAC2, analog-to-digital converter chip ADC, hot wire resistors Rt1 to Rt4, current sampling resistors Rs1 and Rs2, differential amplifier U3, resistors R1 to R10, capacitors C1 and C2, microcontroller MCU, electrical isolation device U4, and high voltage power supply VH;

[0020] In this embodiment, the non-inverting input terminal of operational amplifier U1 is connected in series with resistor R2 and then connected to one end of current sampling resistor Rs1. Simultaneously, one end of hot-wire resistor Rt2 is connected, and the other end of Rt2 is connected to one end of hot-wire resistor Rt1. This connection is also made to the inverting input terminal of differential amplifier U3 and connected to GND. The other end of current sampling resistor Rs1 is connected to GND_ISO isolation ground. The other end of hot-wire resistor Rt1 is connected to the emitter of transistor Q2. The collector of transistor Q2 is connected to the high-voltage power supply VH, and the base of transistor Q2 is connected to the collector of transistor Q1. Resistor R5 is connected in parallel. The collector and base of transistor Q2 are connected in series with resistor R4, and the base of transistor Q1 is connected to the output of operational amplifier U1. The emitter of transistor Q1 is connected to GND_ISO for isolation. The inverting input of operational amplifier U1 is connected to the output of digital-to-analog converter chip DAC1. Resistor R3 is connected in parallel to the output and inverting input of operational amplifier U1. Capacitor C1 is connected in parallel with resistor R3. The digital signal line of digital-to-analog converter chip DAC1 is connected to microcontroller MCU through electrical isolation device U4. The negative power supply input of operational amplifier U1 is connected to GND_ISO for isolation.

[0021] In this embodiment, the non-inverting input terminal of operational amplifier U2 is connected in series with resistor R7 and then connected to one end of current sampling resistor Rs2, and simultaneously connected to one end of hot wire resistor Rt4. The other end of hot wire resistor Rt4 is connected to one end of hot wire resistor Rt3, which is also connected to the non-inverting input terminal of differential amplifier U3. The negative power supply input terminal of differential amplifier U3 is connected to GND ground. The other end of current sampling resistor Rs2 is connected to GND_ISO isolation ground. The other end of hot wire resistor Rt3 is connected to the emitter of transistor Q4. The collector of transistor Q4 is connected to the high voltage power supply VH. The base of transistor Q4 is connected to the collector of transistor Q3. Resistor R10 is connected in parallel between the collector and base of transistor Q4. The base of transistor Q3 is connected in series with resistor R9 and then connected to the output of operational amplifier U2. The emitter of transistor Q3 is connected to GND_ISO for isolation. The inverting input of operational amplifier U2 is connected to the output of digital-to-analog converter chip DAC2. Resistor R8 is connected in parallel between the output and inverting input of operational amplifier U2. Capacitor C2 is connected in parallel with resistor R8. The digital signal line of digital-to-analog converter chip DAC2 is connected to microcontroller MCU through electrical isolation device U4. The negative power supply input of operational amplifier U2 is connected to GND_ISO for isolation.

[0022] In this embodiment, the digital-to-analog converter chips DAC1 and DAC2 are used to set the constant current value Iset of the bridge.

[0023] In this embodiment, operational amplifiers U1 and U2 are used to adjust the actual current value to the set constant current value.

[0024] In this embodiment, Q1 and Q2 constitute the current regulation execution circuit, and Rs1, U1, Q1, Q2, Rt1, and Rt2 together form a current negative feedback regulation circuit to stabilize the current output. Similarly, Q3 and Q4 also constitute the current regulation execution circuit, and Rs2, U2, Q3, Q4, Rt3, and Rt4 together form another current negative feedback regulation circuit to stabilize the current output.

[0025] More specifically, transistors Q1 and Q2 operate in the linear amplification region. By adjusting the conduction level of transistors Q1 and Q2, the current flowing through the current sampling resistor Rs1 can be adjusted. When the resistance of Rt1 or Rt2 increases due to heat dissipation, the current flowing through Rs1 decreases, the output of U1 decreases, the base voltage of Q1 decreases, and the base current of Q1 decreases. Conversely, the base voltage of Q2 increases, the base current of Q2 increases, the emitter current of Q2 increases, and the current through Rs1 increases. Once stable, transistors Q3 and Q4 operate in the linear amplification region. By adjusting the turn-on degree of transistors Q3 and Q4, the current flowing through sampling resistor Rs2 can be adjusted. When the resistance of Rt3 or Rt4 increases due to heat dissipation, the current flowing through Rs2 decreases, the output of U2 decreases, the base voltage of Q3 decreases, the base current of Q3 decreases, the base voltage of Q4 increases, the base current of Q4 increases, the emitter current of Q4 increases, the current in Rs2 increases, and the current in Rs2 is stabilized.

[0026] In this embodiment, resistor R5 provides bias current for Q2, and the combined effect of Q1 and R5 enables Q2 to operate in the linear amplification region.

[0027] In this embodiment, resistor R10 provides bias current for Q4, and Q3 and R10 work together to make Q4 operate in the linear amplification region.

[0028] In this embodiment, the current sampling resistors Rs1 and Rs2 are both precision resistors with equal resistance values.

[0029] In this embodiment, the output terminal Vo of the differential amplifier U3 is connected to the input terminal of the analog-to-digital converter (ADC), and the digital signal line of the ADC is connected to the MCU.

[0030] In this embodiment, the thermal conductivity measurement signal (the output signal of the bridge) is output to the analog-to-digital converter (ADC) chip via the differential amplifier circuit U3. The microcontroller (MCU) samples the ADC reading. During circuit zeroing, the values ​​of Irs1 and Irs2 are adjusted so that the output voltage of the differential amplifier U3 is close to 0V, at which point zeroing is considered complete. The relationship between each current and voltage satisfies the following equation:

[0031] Bridge current setting: Iset; DAC voltage setting: Vset; Rs = Rs1 = Rs2; Iset = Irs1 + Irs2; Idelt = (Irs1 - Irs2) / 2; Iset = (Irs1 - Idelt) * 2 = (Irs2 + Idelt) * 2; Vdac1 = Irs1 * Rs1; Vdac2 = Irs2 * Rs2; where Rs is the hot wire resistance; Iset is the set hot wire current, i.e., the constant current value mentioned above; Idelt is the intermediate variable value (current difference); Vdac1 and Vdac2 are the output voltage values ​​of the digital-to-analog converter chips DAC1 and DAC2, controlled by the MCU.

[0032] In this embodiment, Rs1 and Rs2 are the current sampling resistors of the two constant current circuits of the bridge. The voltage across the current sampling resistors is input to the non-inverting input terminals of operational amplifiers U1 and U2. The inverting input terminals of operational amplifiers U1 and U2 are connected to the output terminals of digital-to-analog converter chips DAC1 and DAC2. The output terminals of operational amplifiers U1 and U2 control the conduction degree of transistors Q1, Q2, Q3, and Q4, thereby controlling the current magnitude of the bridge circuit.

[0033] It should be noted that the bridge circuit includes hot wire resistors Rt1 to Rt4.

[0034] In summary, the thermal conductivity detection circuit with dual constant current source bridges described above achieves an adjustable constant current, high precision, and zero-adjustable thermal conductivity detection circuit in a low-cost manner.

[0035] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A thermal conductivity detection circuit based on a dual constant current source bridge, characterized in that, The system includes a first hot wire resistor module, a second hot wire resistor module, a first current negative feedback adjustment module, a second current negative feedback adjustment module, a detection module, a current setting module, and a microcontroller. The first hot wire resistor module is connected to the first current negative feedback adjustment module and also to the input terminal of the detection module. The second hot wire resistor module is connected to the second current negative feedback adjustment module and also to the input terminal of the detection module. The current setting module is connected to the output terminal of the microcontroller and to the input terminals of both the first and second current negative feedback adjustment modules. The detection module is connected to the input terminal of the microcontroller.

2. The thermal conductivity detection circuit based on a dual constant current source bridge according to claim 1, characterized in that, The first hot wire resistor module includes hot wire resistors Rt1 and Rt2, which are connected in series and located in the thermal conductivity cell. The input terminal of the detection module is connected between the hot wire resistors Rt1 and Rt2.

3. The thermal conductivity detection circuit based on a dual constant current source bridge according to claim 2, characterized in that, The second hot wire resistor module includes hot wire resistors Rt3 and Rt4, which are connected in series and located in the thermal conductivity cell. The input terminal of the detection module is connected between the hot wire resistors Rt3 and Rt4.

4. The thermal conductivity detection circuit based on a dual constant current source bridge according to claim 3, characterized in that, The first current negative feedback regulation module includes transistors Q1 and Q2, operational amplifier U1, and current sampling resistor Rs1. The non-inverting input terminal of operational amplifier U1 is connected in series with resistor R2 and then connected to one end of the current sampling resistor Rs1. Simultaneously, one end of a hot-wire resistor Rt2 is connected to this resistor. The other end of the hot-wire resistor Rt2 is connected to one end of the hot-wire resistor Rt1. The other end of the current sampling resistor Rs1 is connected to GND_ISO isolation ground. The other end of the hot-wire resistor Rt1 is connected to the emitter of transistor Q2. The collector of transistor Q2... The electrode is connected to the high-voltage power supply VH. The base of transistor Q2 is connected to the collector of transistor Q1. The base of transistor Q1 is connected in series with resistor R4 and then connected to the output of operational amplifier U1. The emitter of transistor Q1 is connected to GND_ISO for isolation. The inverting input of operational amplifier U1 is connected to the output of the current setting module. Resistor R3 is connected in parallel to the output and inverting input of operational amplifier U1. Capacitor C1 is connected in parallel with resistor R3. The negative power supply input of operational amplifier U1 is connected to GND_ISO for isolation.

5. A thermal conductivity detection circuit based on a dual constant current source bridge according to claim 4, characterized in that, The first current negative feedback regulation module includes transistors Q3 and Q4, operational amplifier U2, and current sampling resistor Rs2. The non-inverting input terminal of operational amplifier U2 is connected in series with resistor R7 and then connected to one end of current sampling resistor Rs2, and simultaneously connected to one end of hot wire resistor Rt4. The other end of hot wire resistor Rt4 is connected to one end of hot wire resistor Rt3. The other end of current sampling resistor Rs2 is connected to GND_ISO isolation ground. The other end of hot wire resistor Rt3 is connected to the emitter of transistor Q4. The collector of transistor Q4... The electrode is connected to the high-voltage power supply VH. The base of transistor Q4 is connected to the collector of transistor Q3. The base of transistor Q3 is connected in series with resistor R9 and then connected to the output of operational amplifier U2. The emitter of transistor Q3 is connected to GND_ISO isolation ground. The inverting input of operational amplifier U2 is connected to the output of the current setting module. Resistor R8 is connected in parallel to the output and inverting input of operational amplifier U2. Capacitor C2 is connected in parallel with resistor R8. The negative power supply input of operational amplifier U2 is connected to GND_ISO isolation ground.

6. A thermal conductivity detection circuit based on a dual constant current source bridge according to claim 5, characterized in that, The current setting module includes digital-to-analog converter chips DAC1 and DAC2; the input terminal of digital-to-analog converter chip DAC1 is connected to microcontroller MCU through electrical isolation device U4, and the output terminal is connected to the inverting input terminal of operational amplifier U1; The input terminal of the digital-to-analog converter chip DAC2 is connected to the microcontroller MCU through the electrical isolation device U4, and the output terminal is connected to the inverting input terminal of the operational amplifier U2.

7. A thermal conductivity detection circuit based on a dual constant current source bridge according to claim 6, characterized in that, The detection module includes a differential amplifier U3 and an analog-to-digital converter (ADC). The inverting input of the differential amplifier U3 is connected between hot wire resistors Rt1 and Rt2 and connected to GND. The non-inverting input of the differential amplifier U3 is connected between hot wire resistors Rt3 and Rt4. The output of the differential amplifier U3 is connected to the input of the ADC. The output of the ADC is connected to the input of the microcontroller (MCU). The negative power supply input of the differential amplifier U3 is connected to GND.

8. A thermal conductivity detection circuit based on a dual constant current source bridge according to claim 7, characterized in that, The thermal conductivity detection circuit based on the dual constant current source bridge also includes bias resistors R5 and R10, which are connected in parallel between the collector and base of transistor Q2, and resistor R10 is connected in parallel between the collector and base of transistor Q4.

9. A thermal conductivity detection circuit based on a dual constant current source bridge according to claim 7, characterized in that, The current sampling resistors Rs1 and Rs2 are both precision resistors with equal resistance values.

10. A thermal conductivity detection circuit based on a dual constant current source bridge according to claim 7, characterized in that, When zeroing the thermal conductivity detection circuit based on the dual constant current source bridge, adjust the magnitudes of the current Irs1 on the current sampling resistor Rs1 and the current Irs2 on the current sampling resistor Rs2 so that the output voltage of the differential amplifier U3 is close to 0V, which means the zeroing is considered complete.

Images