A temperature sampling circuit with precision calibration function

Abstract

The present invention provides a temperature sampling circuit with a precision calibration function, including a thermistor RT1, a constant current circuit, a differential sampling circuit, a follower circuit, a precision processing circuit, an AD chip and an MCU chip. The power supply end of the thermistor RT1 is powered by the constant current circuit, and the temperature signal is output by the follower circuit, and the temperature signal output by the follower circuit is connected to the MCU chip; the input end of the precision processing circuit is connected to the output end of the follower circuit, and the output end is connected to the MCU chip. A first digital potentiometer RW1 is provided in the constant current circuit, and a second digital potentiometer RW2 and a third digital potentiometer RW3 are provided in the precision processing circuit, and these three potentiometers are all controlled by the MCU chip. The signal of the temperature sampling circuit can be placed in an ideal working range, and the sampling accuracy can be calibrated and corrected. It has the characteristics of a wide sampling temperature range and high sampling temperature accuracy, and ensures good detection accuracy in a system with a large detection temperature range.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature detection, and in particular to a temperature sampling circuit with a precision calibration function. Background Art

[0002] In more important systems, temperature monitoring is a key function, which generally uses a thermistor and cooperates with a signal conditioning circuit, and then uploads the data to the MCU chip through an AD conversion chip. Since the resistance of the thermistor changes greatly when the temperature changes, this type of temperature detection circuit can generally only guarantee sampling accuracy within a small range, especially when the detection temperature range is large, the temperature detection accuracy is more difficult to guarantee.

[0003] In a system with a large temperature detection range, since the resistance of the thermistor varies greatly, the voltage amplitude at both ends also varies greatly. Since the characteristic parameters of the hardware circuit vary under different working conditions, it is difficult to ensure good detection accuracy when the temperature detection range is large. Summary of the invention

[0004] In order to solve the technical problem raised by the background technology, the present invention provides a temperature sampling circuit with a precision calibration function, which can ensure good detection accuracy in a system with a large detection temperature range.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A temperature sampling circuit with a precision calibration function comprises a thermistor RT1, a constant current circuit, a differential sampling circuit, a follower circuit, a precision processing circuit, a first AD chip, a second AD chip, a third AD chip and an MCU chip.

[0007] The input end of the differential sampling circuit is connected to the constant current circuit to collect the set current value of the constant current circuit, and the output end is connected to the MCU chip via the first AD chip.

[0008] The power supply end of the thermistor RT1 is powered by the constant current circuit, the output end of the thermistor RT1 is connected to the follower circuit, the follower circuit outputs a temperature signal, and the temperature signal output by the follower circuit is connected to the MCU chip via the second AD chip;

[0009] The input end of the precision processing circuit is connected to the output end of the follower circuit, and the output end of the precision processing circuit is connected to the MCU chip via the third AD chip.

[0010] A first digital potentiometer RW1 is provided in the constant current circuit, and a second digital potentiometer RW2 and a third digital potentiometer RW3 are provided in the precision processing circuit. These three potentiometers are all controlled by the MCU chip.

[0011] The set current value of the constant current circuit and the temperature signal output by the follower circuit collected by the first AD chip and the second AD chip respectively are sent to the MCU chip as auxiliary information for the MCU chip to judge the working status of the constant current circuit and the follower circuit. The temperature signal collected by the third AD chip is sent to the MCU chip as the output value of the temperature signal for temperature calibration.

[0012] Furthermore, the constant current circuit is composed of a current limiting resistor R1, a reference chip Z1, a first operational amplifier IC1, a first in-phase resistor R2, a first inverting resistor R3, a first in-phase feedback resistor R4, a first inverting feedback resistor R5, a second operational amplifier IC2, a third operational amplifier IC3, a current detection resistor R6, a first digital potentiometer RW1, and a power amplifier transistor Q1. Its output current is powered by the thermistor RT1, and its output current amplitude is set by the first digital potentiometer RW1.

[0013] The current limiting resistor R1 and the reference chip Z1 are connected in series and powered by VCC. A reference voltage is formed at both ends of the reference chip Z1. After being followed by the first operational amplifier IC1, it is sent to the non-inverting end of the second operational amplifier IC2 through the first non-inverting resistor R2. The first non-inverting feedback resistor R4 is connected to the non-inverting input end of the second operational amplifier IC2 and the output end of the third operational amplifier IC3. The first inverting resistor R3 is connected to the inverting input end of the second operational amplifier IC2 to the ground potential. The output end of the second operational amplifier IC2 is connected to the base of the power amplifier transistor Q1. The collector of the power amplifier transistor Q1 is connected to VCC through the current detection resistor R6. The emitter of the power amplifier transistor Q1 is connected to the first inverting feedback resistor R5 and the upper end of the first digital potentiometer RW1. The other end of the first inverting feedback resistor R5 is connected to the inverting input end of the second operational amplifier IC2. The lower end of the first digital potentiometer RW1 is connected to the non-inverting input end of the third operational amplifier IC3 and serves as the current output end of the constant current circuit. The inverting input end of the third operational amplifier IC3 is connected to the output end.

[0014] When the voltage across the reference chip Z1 is fixed, the amplitude of the current flowing through the thermistor RT1 can be adjusted by adjusting the resistance of the first digital potentiometer RW1.

[0015] Furthermore, the differential sampling circuit is composed of a second in-phase resistor R7, a first in-phase lower voltage-dividing resistor R9, a second in-phase resistor R8, a second inverting feedback resistor R10, and a fourth operational amplifier IC4. The differential sampling circuit uses the voltage across the current detection resistor R6 in the constant current circuit as a signal input, and the output signal reflects the output current amplitude of the constant current circuit and is sent to the first AD chip AD1.

[0016] Furthermore, the following circuit is composed of a fifth operational amplifier IC5, whose inverting input terminal is connected to the output terminal, and sends the voltage across the thermistor RT1 to the precision processing circuit and the second AD chip AD2 after following the voltage.

[0017] Furthermore, the precision processing circuit is composed of a third inverting resistor R11, a second inverting feedback resistor R13, a third in-phase resistor R12, a second in-phase lower voltage divider resistor R14, a first zero drift adjustment resistor R15, a second zero drift adjustment resistor R16, a sixth operational amplifier IC6, a second digital potentiometer RW2, and a third digital potentiometer RW3.

[0018] The output voltage signal of the follower resistor is divided by the third in-phase resistor R12 and the second in-phase lower voltage-dividing resistor R14 and then sent to the in-phase input terminal of the sixth operational amplifier IC6. The third inverting resistor R11 is connected to the inverting input terminal and the ground potential of the sixth operational amplifier IC6. The second inverting feedback resistor R13 and the second digital potentiometer RW2 are connected in series and connected to the inverting input terminal and the output terminal of the sixth operational amplifier IC6. The zero drift adjustment port of the sixth operational amplifier IC6 is respectively connected to the first zero drift adjustment resistor R15 and the second zero drift adjustment resistor R16. The other ends of the first zero drift adjustment resistor R15 and the second zero drift adjustment resistor R16 are connected to the third digital potentiometer RW3. The adjustment port of the third digital potentiometer RW3 is connected to the ground potential.

[0019] The first zero drift adjustment resistor R15, the second zero drift adjustment resistor R16, and the third digital potentiometer RW3 are used to adjust the zero drift signal when the thermistor RT1 is short-circuited. The second inverting feedback resistor R13 and the second digital potentiometer RW2 are connected in series to adjust the amplification factor of the precision processing circuit.

[0020] The output signal of the precision processing circuit is sent to the third AD chip AD3.

[0021] The calibration method of the temperature sampling circuit with precision calibration function comprises the following steps:

[0022] The current amplitude flowing through the thermistor RT1 is adjusted by adjusting the resistance value of the first digital potentiometer RW1;

[0023] The amplification factor of the precision processing circuit is adjusted by adjusting the second digital potentiometer RW2;

[0024] The zero drift signal when the thermistor RT1 is short-circuited is adjusted by adjusting the third digital potentiometer RW3;

[0025] 1) The third digital potentiometer RW3 is used to set the zero drift value, which is required to be adjusted to zero;

[0026] 2) When the resistance of the thermistor RT1 is low, the amplitude of the collected temperature signal is low. The MCU chip extracts the amplitude of the temperature signal collected by the second AD chip AD2. If it is confirmed that the amplitude of the currently collected temperature signal exceeds the set low threshold range, the MCU chip reduces the resistance of the first digital potentiometer RW1 to increase the output current of the constant current circuit; and reduces the resistance of the second digital potentiometer RW2 to reduce the amplification factor; at the same time, the MCU chip identifies the actual output current of the constant current circuit through the signal reported by the first AD chip AD1.

[0027] 3) Similarly, when the resistance of thermistor RT1 is high, the amplitude of the collected temperature signal is high. The MCU chip extracts the amplitude of the temperature signal collected by the second AD chip AD2. If it is confirmed that the amplitude of the currently collected temperature signal exceeds the set high threshold range, the MCU chip increases the resistance of the first digital potentiometer RW1 to reduce the output current of the constant current circuit; and increases the resistance of the second digital potentiometer RW2 to increase the amplification factor.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The circuit scheme of the present invention has the function of adjusting zero drift through a digital potentiometer, and has the function of identifying the amplitude of the voltage signal at both ends of the thermistor, and adjusting the constant current output current and the amplification factor of the precision processing circuit in multiple gears. It can make the signal of the temperature sampling circuit in an ideal working range, calibrate and correct the sampling accuracy, and has the characteristics of wide sampling temperature range and high sampling temperature accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural block diagram of a temperature sampling circuit with precision calibration function of the present invention;

[0031] Figure 2 The invention discloses a circuit diagram of a temperature sampling circuit with a precision calibration function.

[0032] In the figure: 1- constant current circuit 2- differential sampling circuit 3- following circuit 4- precision processing circuit. DETAILED DESCRIPTION

[0033] The specific implementation modes provided by the present invention are described in detail below with reference to the accompanying drawings.

[0034] like Figure 1-2 As shown, a temperature sampling circuit with precision calibration function includes a thermistor RT1, a constant current circuit 1, a differential sampling circuit 2, a follower circuit 3, a precision processing circuit 4, a first AD chip, a second AD chip, a third AD chip and an MCU chip.

[0035] The input end of the differential sampling circuit 2 is connected to the constant current circuit 1 to collect the set current value of the constant current circuit 1, and the output end is connected to the MCU chip via the first AD chip.

[0036] The power supply end of the thermistor RT1 is powered by the constant current circuit 1, the output end of the thermistor RT1 is connected to the follower circuit 3, the follower circuit 3 outputs a temperature signal, and the temperature signal output by the follower circuit 3 is connected to the MCU chip via the second AD chip;

[0037] The input end of the precision processing circuit 4 is connected to the output end of the follower circuit 3 , and the output end of the precision processing circuit 4 is connected to the MCU chip via the third AD chip.

[0038] A first digital potentiometer RW1 is provided in the constant current circuit, and a second digital potentiometer RW2 and a third digital potentiometer RW3 are provided in the precision processing circuit. These three potentiometers are all controlled by the MCU chip.

[0039] The MCU chip collects the set current value of the constant current circuit 1 through the first AD chip; the MCU chip collects the temperature signal output by the follower circuit 3 through the second AD chip, and extracts the amplitude information of the collected temperature signal; the MCU chip collects the temperature signal output by the precision processing circuit 4 through the third AD chip as the output value of the final temperature signal after precision processing.

[0040] The constant current circuit 1 is composed of a current limiting resistor R1, a reference chip Z1, a first operational amplifier IC1, a first in-phase resistor R2, a first inverting resistor R3, a first in-phase feedback resistor R4, a first inverting feedback resistor R5, a second operational amplifier IC2, a third operational amplifier IC3, a current detection resistor R6, a first digital potentiometer RW1, and a power amplifier transistor Q1. Its output current is powered by the thermistor RT1, and its output current amplitude is set by the first digital potentiometer RW1.

[0041] The current limiting resistor R1 and the reference chip Z1 are connected in series and powered by VCC. A reference voltage is formed at both ends of the reference chip Z1. After being followed by the first operational amplifier IC1, it is sent to the non-inverting end of the second operational amplifier IC2 through the first non-inverting resistor R2. The first non-inverting feedback resistor R4 is connected to the non-inverting input end of the second operational amplifier IC2 and the output end of the third operational amplifier IC3. The first inverting resistor R3 is connected to the inverting input end of the second operational amplifier IC2 to the ground potential. The output end of the second operational amplifier IC2 is connected to the base of the power amplifier transistor Q1. The collector of the power amplifier transistor Q1 is connected to VCC through the current detection resistor R6. The emitter of the power amplifier transistor Q1 is connected to the first inverting feedback resistor R5 and the upper end of the first digital potentiometer RW1. The other end of the first inverting feedback resistor R5 is connected to the inverting input end of the second operational amplifier IC2. The lower end of the first digital potentiometer RW1 is connected to the non-inverting input end of the third operational amplifier IC3 and serves as the current output end of the constant current circuit 1. The inverting input end of the third operational amplifier IC3 is connected to the output end.

[0042] The reference chip Z1 is a voltage stabilizing chip.

[0043] In general design, the first in-phase resistor R2, the first in-phase resistor R3, the first in-phase feedback resistor R4, and the first in-phase feedback resistor R5 generally have the same value.

[0044] When the voltage across the reference chip Z1 is fixed, the amplitude of the current flowing through the thermistor RT1 can be adjusted by adjusting the resistance of the first digital potentiometer RW1.

[0045] The differential sampling circuit 2 is composed of a second in-phase resistor R7, a first in-phase lower voltage-dividing resistor R9, a second in-phase resistor R8, a second inverting feedback resistor R10, and a fourth operational amplifier IC4. The differential sampling circuit uses the voltage across the current detection resistor R6 in the constant current circuit as a signal input, and the output signal reflects the output current amplitude of the constant current circuit 1 and is sent to the first AD chip AD1.

[0046] The following circuit 3 is composed of a fifth operational amplifier IC5, whose inverting input terminal is connected to the output terminal, and sends the voltage across the thermistor RT1 to the precision processing circuit 4 and the second AD chip AD2 after following the voltage.

[0047] The precision processing circuit 4 is composed of a third inverting resistor R11, a second inverting feedback resistor R13, a third in-phase resistor R12, a second in-phase lower voltage divider resistor R14, a first zero drift adjustment resistor R15, a second zero drift adjustment resistor R16, a sixth operational amplifier IC6, a second digital potentiometer RW2, and a third digital potentiometer RW3;

[0048] The output voltage signal of the follower resistor is divided by the third in-phase resistor R12 and the second in-phase lower voltage-dividing resistor R14 and then sent to the in-phase input terminal of the sixth operational amplifier IC6. The third inverting resistor R11 is connected to the inverting input terminal and the ground potential of the sixth operational amplifier IC6. The second inverting feedback resistor R13 and the second digital potentiometer RW2 are connected in series and connected to the inverting input terminal and the output terminal of the sixth operational amplifier IC6. The zero drift adjustment port of the sixth operational amplifier IC6 is respectively connected to the first zero drift adjustment resistor R15 and the second zero drift adjustment resistor R16. The other ends of the first zero drift adjustment resistor R15 and the second zero drift adjustment resistor R16 are connected to the third digital potentiometer RW3. The adjustment port of the third digital potentiometer RW3 is connected to the ground potential.

[0049] The first zero drift adjustment resistor R15, the second zero drift adjustment resistor R16, and the third digital potentiometer RW3 are used to adjust the zero drift signal when the thermistor RT1 is short-circuited. The second inverting feedback resistor R13 and the second digital potentiometer RW2 are connected in series to adjust the amplification factor of the precision processing circuit 4.

[0050] The output signal of the precision processing circuit 4 is sent to the third AD chip AD3.

[0051] The calibration method of the temperature sampling circuit with precision calibration function comprises the following steps:

[0052] The current amplitude flowing through the thermistor RT1 is adjusted by adjusting the resistance value of the first digital potentiometer RW1;

[0053] The amplification factor of the precision processing circuit is adjusted by adjusting the second digital potentiometer RW2;

[0054] The zero drift signal when the thermistor RT1 is short-circuited is adjusted by adjusting the third digital potentiometer RW3;

[0055] 1) The third digital potentiometer RW3 is used to set the zero drift value, which is required to be adjusted to zero;

[0056] 2) When the resistance of the thermistor RT1 is low, the amplitude of the collected temperature signal is low. The MCU chip extracts the amplitude of the temperature signal collected by the second AD chip AD2. If it is confirmed that the amplitude of the currently collected temperature signal exceeds the set low threshold range, the MCU chip reduces the resistance of the first digital potentiometer RW1 to increase the output current of the constant current circuit; and reduces the resistance of the second digital potentiometer RW2 to reduce the amplification factor; at the same time, the MCU chip identifies the actual output current of the constant current circuit through the signal reported by the first AD chip AD1.

[0057] 3) Similarly, when the resistance of thermistor RT1 is high, the amplitude of the collected temperature signal is high. The MCU chip extracts the amplitude of the temperature signal collected by the second AD chip AD2. If it is confirmed that the amplitude of the currently collected temperature signal exceeds the set high threshold range, the MCU chip increases the resistance of the first digital potentiometer RW1 to reduce the output current of the constant current circuit; and increases the resistance of the second digital potentiometer RW2 to increase the amplification factor.

[0058] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A temperature sampling circuit with precision calibration function, characterized in that: It includes a thermistor RT1, a constant current circuit, a differential sampling circuit, a follower circuit, a precision processing circuit, a first AD chip, a second AD chip, a third AD chip and an MCU chip; The input end of the differential sampling circuit is connected to the constant current circuit to collect the set current value of the constant current circuit, and the output end is connected to the MCU chip via the first AD chip; The power supply end of the thermistor RT1 is powered by the constant current circuit, the output end of the thermistor RT1 is connected to the follower circuit, the follower circuit outputs a temperature signal, and the temperature signal output by the follower circuit is connected to the MCU chip via the second AD chip; The input end of the precision processing circuit is connected to the output end of the follower circuit, and the output end of the precision processing circuit is connected to the MCU chip via the third AD chip; A first digital potentiometer RW1 is provided in the constant current circuit, a second digital potentiometer RW2 and a third digital potentiometer RW3 are provided in the precision processing circuit, and these three potentiometers are all controlled by the MCU chip; The MCU chip collects the set current value of the constant current circuit through the first AD chip; the MCU chip collects the temperature signal output by the follower circuit through the second AD chip, and extracts the amplitude information of the collected temperature signal; the MCU chip collects the temperature signal output by the precision processing circuit through the third AD chip as the output value of the final temperature signal after precision processing.

2. The temperature sampling circuit with precision calibration function according to claim 1, characterized in that: The constant current circuit is composed of a current limiting resistor R1, a reference chip Z1, a first operational amplifier IC1, a first in-phase resistor R2, a first inverting resistor R3, a first in-phase feedback resistor R4, a first inverting feedback resistor R5, a second operational amplifier IC2, a third operational amplifier IC3, a current detection resistor R6, a first digital potentiometer RW1, and a power amplifier transistor Q1. The output current is powered by the thermistor RT1, and the amplitude of the output current is set by the first digital potentiometer RW1. The current limiting resistor R1 and the reference chip Z1 are connected in series and powered by the power supply VCC. A reference voltage is formed at both ends of the reference chip Z1. After being followed by the first operational amplifier IC1, it is sent to the non-inverting end of the second operational amplifier IC2 through the first non-inverting resistor R2. The first non-inverting feedback resistor R4 is connected between the non-inverting input end of the second operational amplifier IC2 and the output end of the third operational amplifier IC3. The first inverting resistor R3 connects the inverting input end of the second operational amplifier IC2 to the ground potential. The output end of the second operational amplifier IC2 is connected to the base of the power amplifier transistor Q1. The collector of the power amplifier transistor Q1 is connected to VCC through the current detection resistor R6. The emitter of the power amplifier transistor Q1 is connected to the first inverting feedback resistor R5 and the upper end of the first digital potentiometer RW1. The other end of the first inverting feedback resistor R5 is connected to the inverting input end of the second operational amplifier IC2. The lower end of the first digital potentiometer RW1 is connected to the non-inverting input end of the third operational amplifier IC3 and serves as the current output end of the constant current circuit. The inverting input end of the third operational amplifier IC3 is connected to the output end. When the voltage across the reference chip Z1 is fixed, the amplitude of the current flowing through the thermistor RT1 can be adjusted by adjusting the resistance of the first digital potentiometer RW1.

3. The temperature sampling circuit with precision calibration function according to claim 2, characterized in that: The differential sampling circuit is composed of a second in-phase resistor R7, a first in-phase voltage-dividing resistor R9, a second in-phase resistor R8, a second inverting feedback resistor R10, and a fourth operational amplifier IC4. The differential sampling circuit uses the voltage across the current detection resistor R6 in the constant current circuit as a signal input, and the output signal reflects the output current amplitude of the constant current circuit and is sent to the first AD chip.

4. The temperature sampling circuit with precision calibration function according to claim 1, characterized in that: The following circuit is composed of a fifth operational amplifier IC5, whose inverting input terminal is connected to the output terminal, and sends the voltage across the thermistor RT1 to the precision processing circuit and the second AD chip after following the voltage.

5. The temperature sampling circuit with precision calibration function according to claim 1, characterized in that: The precision processing circuit is composed of a third inverting resistor R11, a second inverting feedback resistor R13, a third in-phase resistor R12, a second in-phase lower voltage divider resistor R14, a first zero drift adjustment resistor R15, a second zero drift adjustment resistor R16, a sixth operational amplifier IC6, a second digital potentiometer RW2, and a third digital potentiometer RW3; The voltage signal output by the follower circuit is divided by the third in-phase resistor R12 and the second in-phase lower voltage-dividing resistor R14 and then sent to the in-phase input terminal of the sixth operational amplifier IC6. The third inverting resistor R11 is connected to the inverting input terminal and the ground potential of the sixth operational amplifier IC6. The second inverting feedback resistor R13 and the second digital potentiometer RW2 are connected in series and connected to the inverting input terminal and the output terminal of the sixth operational amplifier IC6. The zero drift adjustment port of the sixth operational amplifier IC6 is respectively connected to the first zero drift adjustment resistor R15 and the second zero drift adjustment resistor R16. The other ends of the first zero drift adjustment resistor R15 and the second zero drift adjustment resistor R16 are connected to the third digital potentiometer RW3. The adjustment port of the third digital potentiometer RW3 is connected to the ground potential. The first zero drift adjustment resistor R15, the second zero drift adjustment resistor R16 and the third digital potentiometer RW3 are connected to adjust the zero drift signal when the thermistor RT1 is short-circuited, and the second inverting feedback resistor R13 and the second digital potentiometer RW2 are connected in series to adjust the amplification factor of the precision processing circuit; The output signal of the precision processing circuit is sent to the third AD chip.

6. A calibration method for a temperature sampling circuit with a precision calibration function according to any one of claims 1 to 5, characterized in that: These include: The current amplitude flowing through the thermistor RT1 is adjusted by adjusting the resistance value of the first digital potentiometer RW1; The amplification factor of the precision processing circuit is adjusted by adjusting the second digital potentiometer RW2; The zero drift signal when the thermistor RT1 is short-circuited is adjusted by adjusting the third digital potentiometer RW3; 1) The third digital potentiometer RW3 is used to set the zero drift value, which is required to be adjusted to zero; 2) When the resistance of thermistor RT1 is low, the amplitude of the collected temperature signal is low. The MCU chip extracts the amplitude of the temperature signal collected by the second AD chip. If it is confirmed that the amplitude of the currently collected temperature signal exceeds the set low threshold range, the MCU chip adjusts the resistance of the first digital potentiometer RW1 to increase the output current of the constant current circuit; and adjusts the resistance of the second digital potentiometer RW2 to reduce the amplification factor; at the same time, the MCU chip identifies the actual output current of the constant current circuit through the signal reported by the first AD chip; 3) Similarly, when the resistance of thermistor RT1 is high, the amplitude of the collected temperature signal is high. The MCU chip extracts the amplitude of the temperature signal collected by the second AD chip. If it is confirmed that the amplitude of the currently collected temperature signal exceeds the set high threshold range, the MCU chip increases the resistance of the first digital potentiometer RW1 to reduce the output current of the constant current circuit; and increases the resistance of the second digital potentiometer RW2 to increase the amplification factor.

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