Automatic full-scale calibration circuit and calibration method based on pirani vacuum transducer

Abstract

The application discloses an automatic full-scale calibration circuit and method based on a Pirani vacuum transmitter, and relates to the technical field of vacuum measurement.The application can obtain a real-time pressure signal of the Pirani vacuum transmitter and a correction factor of a programmable potentiometer in the automatic full-scale calibration circuit, so as to calculate a compensation gear, and then configure an automatic temperature and full-scale calibration circuit suitable for the Pirani vacuum transmitter, so that full-scale intelligent calibration is realized.The application solves the problems of the traditional potentiometer adjustment, such as the need for manual intervention, the inability to realize dynamic calibration after the aging of the sensor, the complexity of operation, the difficulty in adapting to the changing requirements in actual use, and the inability of the traditional calibration mode to solve the actual output deviation problem of the sensor, and only through the correction of the calculation value by the calibration coefficient, the measurement accuracy requirement cannot be met when the sensor is aging, and the measurement value is likely to exceed the maximum allowable error.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum measurement, and relates to a full-scale calibration technology of an industrial-grade precision vacuum transmitter, in particular to an automatic full-scale calibration circuit and method based on a Pirani vacuum transmitter. BACKGROUND

[0002] A Pirani vacuum transmitter is an instrument that measures vacuum degree based on the characteristic that the thermal conductivity of a gas changes with pressure. Its core principle is the relationship between heat conduction and pressure: in a vacuum environment, the density of gas molecules decreases, causing the thermal conductivity of the gas to decrease. When a heating wire is placed in this environment, the temperature of the heating wire will rise due to the reduced efficiency of heat conduction and convection heat dissipation, which in turn causes the resistance of the heating wire to increase. In actual design, a Pirani vacuum transmitter usually adopts a four-arm Wheatstone bridge structure. One arm is a measurement resistance wire (usually made of tungsten, nickel, etc.), and the other arm is a temperature calibration resistance. The role of the temperature calibration resistance is to eliminate the interference of environmental temperature fluctuations on the measurement results, ensuring that the measurement results only reflect the changes in gas pressure.

[0003] However, there are some problems in the use of Pirani vacuum transmitters. Since it mainly relies on the principle of heat conduction for measurement, and the resistance wire is in a long-term energized heating state (usually with a temperature of up to 200-400℃), it is easy for the surface of the resistance wire to oxidize or the lattice structure to degrade, which in turn causes the resistivity to drift. Changes in the environment and gas temperature have a greater impact on measurement accuracy. When an oxide layer forms on the surface of the resistance wire or material defects occur, the nonlinear relationship between the resistance of the resistance wire and the temperature will deviate from the initial calibration curve, which in turn causes the balance point of the Wheatstone bridge to shift, requiring frequent recalibration.

[0004] In the traditional calibration method, the full-scale calibration of a Pirani vacuum transmitter is usually performed by a one-key calibration function, which multiplies the display value by a calibration coefficient k to make the display value reach 100000 Pa. Although this calibration method has a certain universality and is relatively flexible to operate, its essence is to correct the calculated pressure value by the calibration coefficient, and it does not really solve the problem of actual output deviation of the sensor. When the sensor of a Pirani vacuum transmitter ages, this simple full-scale calibration method will result in measurement data that cannot meet the accuracy requirements, and the measurement display value may exceed the maximum allowable error range. Moreover, the traditional potentiometer adjustment method requires manual intervention and cannot achieve dynamic calibration of the sensor after aging, and the operation process is also relatively complex.

[0005] In summary, the existing technology has the following problems:

[0006] 1. The traditional calibration method cannot solve the problem of actual output deviation of the sensor, and only through the correction of the calculation value by the calibration coefficient, when the sensor is aging, it cannot meet the measurement accuracy requirement, and is easy to lead to the measurement value exceeding the maximum allowable error.

[0007] 2. The traditional potentiometer adjustment needs manual intervention, cannot realize dynamic calibration of the sensor after aging, and is complex to operate, and is difficult to adapt to the change requirement in actual use. SUMMARY

[0008] Based on the problems proposed in the above background technology, the purpose of the present application is to provide an automatic full-scale calibration circuit based on a Pirani vacuum transmitter, which solves the problems of the traditional potentiometer adjustment needing manual intervention, being unable to realize dynamic calibration of the sensor after aging, being complex to operate, being difficult to adapt to the change requirement in actual use, and the traditional calibration method being unable to solve the problem of actual output deviation of the sensor, only being able to correct the calculation value by the calibration coefficient, being unable to meet the measurement accuracy requirement when the sensor is aging, and being easy to lead to the measurement value exceeding the maximum allowable error.

[0009] The present application is realized by the following technical solutions:

[0010] The present application provides an automatic full-scale calibration circuit based on a Pirani vacuum transmitter, which comprises

[0011] a four-arm programmable bridge, an amplifier U2 and a triode Q1;

[0012] The four-arm programmable bridge comprises a balance bridge arm, a measurement arm, a temperature calibration arm and a full-scale calibration arm connected through a common point;

[0013] The four-arm programmable bridge is connected to the positive and negative input terminals of the amplifier U2, the output terminal of the amplifier U2 is connected to the base of the triode Q1, and the collector and emitter of the triode Q1 are connected to the balance bridge arm in the four-arm programmable bridge.

[0014] Among them, the four-arm programmable bridge sends the sensor signal of the Pirani vacuum transmitter collected to the amplifier U2, the amplifier U2 generates a control voltage according to the sensor signal, and the triode Q1 generates a working current for adjusting the four-arm programmable bridge according to the control voltage.

[0015] In the above technical solution, the sensor signal of the Pirani vacuum transmitter collected is sent to the amplifier U2 through the four-arm programmable bridge, the amplifier U2 generates a control voltage according to the sensor signal, and the triode Q1 generates a working current for adjusting the four-arm programmable bridge according to the control voltage, thereby effectively overcoming the defects and deficiencies of the traditional calibration method, realizing the automatic full-scale adjustment function under atmospheric conditions, without manual intervention, and ensuring that the sensor can accurately reach the set temperature, thereby significantly reducing the adverse effects of temperature changes and sensor aging on the measurement accuracy of the transmitter, greatly improving the measurement accuracy and reliability, and providing a more efficient, convenient and accurate solution for the calibration and measurement of the Pirani vacuum transmitter.

[0016] In an alternative embodiment, the balance bridge arm includes resistors R3 and R7 in parallel; the measurement arm includes resistor R12; the temperature calibration arm includes resistors R10 and R13 in series; and the full-scale calibration arm includes a programmable potentiometer, resistor R1, and resistor R2, with resistor R1 connected in parallel with the programmable potentiometer and then connected in series with resistor R2.

[0017] In an alternative embodiment, the programmable potentiometer is a digital potentiometer of model AD8400.

[0018] In an alternative embodiment, the amplifier U2 is a precision amplifier of model OP777.

[0019] In an alternative embodiment, the triode Q1 is a triode of model 8050.

[0020] In an alternative embodiment, the automatic full-scale calibration circuit further includes:

[0021] resistors R4, R5, R6, R8, R9, R11, capacitors C1, C2, C3, diodes D1, D2, and D3;

[0022] The resistance R4 is connected in parallel between the collector and the emitter of the triode Q1; the resistance R5 is connected between the base of the triode Q1 and the output of the amplifier U2; the resistance R6 is connected in parallel between the positive input of the amplifier U2 and the positive power supply; the resistance R8 is connected between the common point and the positive input of the amplifier U2; the resistance R9 is connected in series with the capacitor C2; the resistance R11 is connected in series with the capacitor C3 and then connected in parallel with the capacitor C2; the capacitor C2 is connected in parallel with the diode D3 which is connected in parallel between the negative input and the output of the amplifier U2; the diode D1 is connected in reverse parallel with the diode D2, the cathode of the diode D1 is connected with the resistance R8, and the anode of the diode D1 is connected with the resistance R9.

[0023] The second aspect of the present application provides an automatic full-scale calibration method based on a Pirani vacuum transmitter, comprising the following steps:

[0024] An atmospheric pressure signal of the Pirani vacuum transmitter is acquired.

[0025] The Pirani vacuum transmitter is calibrated for stability by the atmospheric pressure signal, and when the Pirani vacuum transmitter reaches a stable state, a filament voltage signal of the Pirani vacuum transmitter is acquired.

[0026] A calibration factor is acquired by an automatic full-scale calibration circuit, and a calibration gear is calculated by the filament voltage signal and the calibration factor.

[0027] The automatic full-scale calibration circuit performs automatic full-scale calibration according to the calibration gear.

[0028] In the above technical solution, the atmospheric pressure signal is acquired by an atmospheric pressure sensor in the Pirani transmitter; the Pirani vacuum transmitter is calibrated for stability by the atmospheric pressure signal, wherein the stability calibration is to determine whether the Pirani transmitter works in an atmospheric pressure environment (i.e. the vacuum cavity is in communication with the atmosphere) by the atmospheric pressure signal, if it works in the atmospheric pressure environment, the controller starts timing, and when the sensor filament temperature and the air thermal conductivity reach a stable state, the sensor filament voltage signal in the Pirani transmitter at this time is acquired.

[0029] The calibration factor is acquired by the automatic full-scale calibration circuit, and the calibration gear of the Pirani vacuum transmitter can be calculated by the filament voltage signal and the calibration factor, the adjustment gear of the programmable potentiometer in the automatic full-scale calibration circuit is calibrated for full-scale by the calibration gear, so as to acquire the compensated pressure signal, which overcomes the defect that the calculated value is only corrected by the calibration coefficient, and when the sensor is aged, the measurement accuracy requirement cannot be met, which easily leads to that the measurement value exceeds the maximum allowable error.

[0030] In an alternative embodiment, the calibration factor is obtained by the automatic full-scale calibration circuit, comprising the following steps:

[0031] a first preset value is written to the programmable potentiometer in the automatic full-scale calibration circuit, through which the stability of the Pirani vacuum transmitter is calibrated, and when the Pirani vacuum transmitter reaches a stable state, the current pressure signal is recorded as a first pressure signal;

[0032] a second preset value is written to the programmable potentiometer, through which the stability of the Pirani vacuum transmitter is calibrated, and when the Pirani vacuum transmitter reaches a stable state, the current pressure signal is recorded as a second pressure signal;

[0033] the absolute value of the difference between the first pressure signal and the second pressure signal is calculated, and the absolute value of the difference is taken as the calibration factor.

[0034] In an alternative embodiment, the first preset value and the second preset value are adjacent in value.

[0035] In an alternative embodiment, the calibration gear is calculated using the filament voltage signal and the calibration factor, comprising:

[0036] CaliVa = | PresetPa - VacuumPa | / K;

[0037] In the above formula, CaliVa is the calibration gear, PresetPa is the preset value, VacuumPa is the filament voltage signal, and K is the calibration factor.

[0038] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0039] The present application obtains the calibration factor through the automatic full-scale calibration circuit, and the calibration gear required by the Pirani vacuum transmitter can be calculated through the filament voltage signal and the calibration factor. The adjustment gear of the programmable potentiometer in the automatic full-scale calibration circuit is calibrated through the calibration gear, so as to obtain the compensated pressure signal. The defect that the calculated value can only be corrected by the calibration coefficient, and the measurement accuracy requirement cannot be met when the sensor is aging, and the measured value is easily beyond the maximum allowable error, is overcome. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be considered as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0041] Figure 1 A principle schematic diagram of an automatic full-scale calibration circuit based on a Pirani vacuum transmitter is provided for Embodiment 1 of the present application;

[0042] Figure 2 A flow schematic diagram of an automatic full-scale calibration method based on a Pirani vacuum transmitter is provided for Embodiment 2 of the present application. DETAILED DESCRIPTION

[0043] In order to make the objects, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application in combination with embodiments and drawings, and the schematic embodiments of the present application and the description thereof are only used for explaining the present application, and do not limit the present application.

[0044] Embodiment 1 provides a principle schematic diagram of an automatic full-scale calibration circuit based on a Pirani vacuum transmitter, as shown in FIG. 1, the automatic full-scale calibration circuit comprises: Figure 1

[0045] a four-arm programmable bridge, an amplifier U2 and a triode Q1;

[0046] The four-arm programmable bridge comprises a balance bridge arm, a measurement arm, a temperature calibration arm and a full-scale calibration arm connected through a common point;

[0047] The four-arm programmable bridge is connected to the positive and negative input terminals of the amplifier U2, the output terminal of the amplifier U2 is connected to the base of the triode Q1, and the collector and emitter of the triode Q1 are connected to the balance bridge arm in the four-arm programmable bridge;

[0048] The four-arm programmable bridge sends the collected sensor signal of the Pirani vacuum transmitter to the amplifier U2, the amplifier U2 generates a control voltage according to the sensor signal, and the triode Q1 generates a working current for adjusting the four-arm programmable bridge according to the control voltage.

[0049] It should be noted that the conventional Pirani vacuum transmitter generally adopts a position button for calibration, and after pressing the button, only the output voltage of the transmitter can be adjusted to the full scale, and the sensor signal of the transmitter itself cannot be directly adjusted, and only the software calibration method is used to make the output signal of the transmitter reach the full-scale value. However, when the temperature changes or the sensor itself ages, the sensor of the transmitter will not reach the set temperature, thereby causing the measurement accuracy to decrease. In addition, there is a more traditional method of adjusting through a potentiometer, which adopts a manual mechanical adjustment method, and the operation process is relatively complex, and the professional skill requirement for the user is relatively high.

[0050] ​The automatic full-scale calibration circuit provided in the embodiment sends the collected sensor signal of the Pirani vacuum transmitter to the amplifier U2 through the four-arm programmable bridge, the amplifier U2 generates a control voltage according to the sensor signal, and the triode Q1 generates a working current for adjusting the four-arm programmable bridge according to the control voltage, thereby effectively overcoming the defects and deficiencies of the traditional calibration method, realizing the automatic full-scale adjustment function under atmospheric conditions, without manual intervention, and ensuring that the sensor can accurately reach the set temperature, thereby significantly reducing the adverse effects of temperature changes and sensor aging on the measurement accuracy of the transmitter, greatly improving the measurement accuracy and reliability, and providing a more efficient, convenient and accurate solution for the calibration and measurement of the Pirani vacuum transmitter.

[0051] In an alternative embodiment, the balance bridge arm includes resistors R3 and R7 in parallel; the measurement arm includes resistor R12; the temperature calibration arm includes resistors R10 and R13 in series; and the full-scale calibration arm includes a programmable potentiometer, resistor R1 and resistor R2, with resistor R1 and the programmable potentiometer in parallel and resistor R1 and resistor R2 in series.

[0052] It should be noted that resistors R3 and R7 are fixed resistors for balancing the bridge; resistor R12 is a sensor filament exposed to vacuum, and its resistance varies with temperature (i.e., vacuum degree); and resistor R13 is a temperature sensor in series with resistor R10 for temperature calibration, and then in parallel with resistor R12 for eliminating the influence of ambient temperature.

[0053] Since the resistance of the resistor wire will fluctuate abnormally after aging, affecting the accuracy of pressure calculation, the circuit in this embodiment connects resistor R1 and the programmable potentiometer in parallel and then connects resistor R1 and resistor R2 in series to form a full-scale calibration arm, which is used to adjust the full-scale voltage and eliminate the influence of resistor wire sensor aging.

[0054] When the Pirani vacuum transmitter starts to pump vacuum, the number of air molecules decreases, the heat dissipation of the filament slows down, the temperature rises, the resistance R12 (i.e., the sensor equation) temperature increases, causing the bridge to be unbalanced, the voltage on resistor R12 increases, causing the signal at the positive and negative input terminals of amplifier U2 to change, and the output voltage output by the output terminal of amplifier U2 to decrease, thereby controlling triode Q1 to decrease the working current of the four-arm programmable bridge, keeping resistor R12 at a constant temperature, detecting the voltage signal output at resistor R12, and converting it into a pressure reading after amplification.

[0055] In an alternative embodiment, the programmable potentiometer is a digital potentiometer of model AD8400.

[0056] In an alternative embodiment, the amplifier U2 is a precision amplifier of model OP777.

[0057] In an alternative embodiment, the triode Q1 is a triode of model 8050.

[0058] In an alternative embodiment, the automatic full-scale calibration circuit further comprises:

[0059] resistor R4, resistor R5, resistor R6, resistor R8, resistor R9, resistor R11, capacitor C1, capacitor C2, capacitor C3, diode D1, diode D2 and diode D3;

[0060] The resistor R4 is connected in parallel between the collector and the emitter of the triode Q1; the resistor R5 is connected between the base of the triode Q1 and the output of the amplifier U2; the resistor R6 is connected in parallel between the positive input of the amplifier U2 and the positive power supply; the resistor R8 is connected between the common point and the positive input of the amplifier U2; the resistor R9 is connected in series with the capacitor C2; the resistor R11 is connected in series with the capacitor C3 and in parallel with the capacitor C2; the capacitor C2 is connected in parallel with the diode D3, which is connected in parallel between the negative input and the output of the amplifier U2; the diode D1 is connected in anti-parallel with the diode D2, the cathode of the diode D1 is connected with the resistor R8, and the anode of the diode D1 is connected with the resistor R9.

[0061] Embodiment 2 of the present application provides an automatic full-scale calibration method based on a Pirani vacuum transmitter, which is used for the automatic full-scale calibration circuit based on a Pirani vacuum transmitter of embodiment 1, as shown in Figure 2 The automatic full-scale calibration method based on a Pirani vacuum transmitter comprises the following steps:

[0062] obtaining an atmospheric pressure signal of the Pirani vacuum transmitter;

[0063] performing stability calibration on the Pirani vacuum transmitter through the atmospheric pressure signal, and obtaining a filament voltage signal of the Pirani vacuum transmitter when the Pirani vacuum transmitter reaches a stable state;

[0064] obtaining a calibration factor through the automatic full-scale calibration circuit, and calculating a calibration gear by using the filament voltage signal and the calibration factor;

[0065] The automatic full-scale calibration circuit performs automatic full-scale calibration according to the calibration gear.

[0066] It should be noted that the atmospheric pressure signal is obtained through an atmospheric pressure sensor in the Pirani transmitter; the atmospheric pressure signal is transmitted to a controller (e.g., a microcontroller) in the automatic full-scale calibration circuit. Figure 2In the MCU), the controller calibrates the Pirani vacuum transmitter by the atmospheric pressure signal, wherein the stability calibration is to determine whether the Pirani transmitter works in the atmospheric pressure environment (i.e. the vacuum cavity is in communication with the atmosphere) by the atmospheric pressure signal, if it works in the atmospheric pressure environment, the controller starts timing, and when the sensor filament temperature and the air thermal conductivity reach a stable state, the sensor filament voltage signal in the Pirani transmitter at this time is obtained.

[0067] The calibration factor is obtained by the automatic full-scale calibration circuit, and the calibration range required by the Pirani vacuum transmitter can be calculated by the filament voltage signal and the calibration factor, and the adjustment range of the programmable potentiometer in the automatic full-scale calibration circuit is calibrated by the calibration range, so as to obtain the compensated pressure signal, which overcomes the defect that only the calculated value is corrected by the calibration coefficient, and when the sensor is aged, the measurement accuracy requirement cannot be met, and the measurement value is easy to exceed the maximum allowable error.

[0068] In an alternative embodiment, the calibration factor is obtained by the automatic full-scale calibration circuit, comprising the following steps:

[0069] The first set value is written to the programmable potentiometer in the automatic full-scale calibration circuit, and the Pirani vacuum transmitter is calibrated by the first set value, and when the Pirani vacuum transmitter reaches a stable state, the current pressure signal is recorded as the first pressure signal;

[0070] The second set value is written to the programmable potentiometer, and the Pirani vacuum transmitter is calibrated by the second set value, and when the Pirani vacuum transmitter reaches a stable state, the current pressure signal is recorded as the second pressure signal;

[0071] The absolute value of the difference between the first pressure signal and the second pressure signal is calculated, and the absolute value of the difference is taken as the calibration factor.

[0072] It should be noted that when the programmable potentiometer is of AD8400 type, the first set value is 0X7E and the second set value is 0X7F; wherein 0X7E and 0X7F are hexadecimal numbers for controlling the programmable potentiometer.

[0073] Specifically, the total resistance of AD8400 is 1kΩ, and the internal part is divided into 256 positions, and only the SPI interface (in this embodiment, the SPI interface is provided in the digital potentiometer of AD8400 type in the MCU) is needed when used. Port, SDI port and CLK port (constitute) to write 0-255 (hexadecimal) any value as a preset value PresetPa, representing the setting B1-W1 segment resistance (PresetPa / 256)*1kΩ. First, first write 0X7E to AD8400, record the current pressure signal after the pressure signal is stable, assuming 100mv; Then write 0X7F to AD8400, record the current pressure signal after the pressure signal is stable, assuming 105mv, then the absolute value of the difference between the two signals 5mv is the programmable potentiometer calibration factor K.

[0074] Wherein the preset value PresetPa is determined by the person skilled in the art according to the actual project situation.

[0075] In an alternative embodiment, the first set value and the second set value are adjacent in value.

[0076] It should be noted that theoretically, the first set value and the second set value are adjacent, but for AD8400, the first set value and the second set value are set to 0X7E and 0x7F, AD8400 is in the middle resistance, which will not cause additional impact on the sensor, so in this embodiment, the two values are preferred; That is, when the programmable potentiometer uses chip AD8400, the first set value is 0X7E, and the second set value is 0X7F.

[0077] In an alternative embodiment, the lamp filament voltage signal and the calibration factor are used to calculate the calibration gear, comprising:

[0078] CaliVa = | PresetPa - VacuumPa | / K;

[0079] In the above formula, CaliVa is the calibration gear, PresetPa is the preset value, VacuumPa is the lamp filament voltage signal, and K is the calibration factor.

[0080] In this embodiment, assuming that the pressure signal to be compensated is PresetPa - VacuumPa = 100mv, and the correction factor is 5mV, then AD8400 needs to increase 20 gear values based on the initial set value. Assuming that the pressure signal to be compensated is PresetPa - VacuumPa = -100mv, and the correction factor is 5mV, then AD8400 needs to decrease 20 gear values based on the initial set value.

[0081] With the calculated calibration gear, the voltage change on the full-scale calibration arm is adjusted, the signal at the positive and negative input terminals of the amplifier U2 changes, thereby adjusting its output voltage to control the transistor Q1, and the transistor Q1 generates an adjustment current for the four-arm programmable bridge according to the output voltage of the amplifier U2, at this time, the resistance R12 (sensor filament) current changes, and then the real-time pressure signal is adjusted to reach the preset value. At this time, the output bit full-scale output of the Pirani vacuum transmitter is 10V (i.e. the pressure value is "1.0x10 5 Pa", the standard atmospheric pressure value) to indicate that the full-scale calibration is complete; at the same time, the controller records the set value written to the programmable potentiometer.

[0082] The method can calculate the compensation gear by obtaining the real-time pressure signal of the Pirani vacuum transmitter and the correction factor of the programmable potentiometer in the automatic full-scale calibration circuit, and then configure the automatic temperature and full-scale calibration circuit suitable for the Pirani vacuum transmitter to realize intelligent full-scale calibration.

[0083] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An automatic full-scale calibration circuit based on a Pirani vacuum transmitter, characterized in that, include: A four-arm programmable bridge, amplifier U2 and transistor Q1; The four-arm programmable bridge includes a balance bridge arm, a measuring arm, a temperature calibration arm, and a full-scale calibration arm connected through a common point. The balance bridge arm includes resistors R3 and R7 connected in parallel. The measuring arm includes resistor R12. The temperature calibration arm includes resistors R10 and R13 connected in series. The full-scale calibration arm includes a programmable potentiometer, resistors R1 and R2, with resistor R1 connected in parallel with the programmable potentiometer and then in series with resistor R2. Resistors R3 and R7 are fixed resistors used for balancing the bridge. Resistor R12 is a sensor filament, an exposed resistance wire whose resistance changes with temperature. Resistor R13 is a temperature sensor, connected in series with resistor R10 for temperature calibration, and then connected in parallel with resistor R12 to eliminate the influence of ambient temperature. The four-arm programmable bridge is connected to the positive and negative input terminals of the amplifier U2, the output terminal of the amplifier U2 is connected to the base of the transistor Q1, and the collector and emitter of the transistor Q1 are connected to the balanced bridge arm of the four-arm programmable bridge. The four-arm programmable bridge sends the sensor signal from the Pirani vacuum transmitter to the amplifier U2. The amplifier U2 generates a control voltage based on the sensor signal, and the transistor Q1 generates an adjustment current for the four-arm programmable bridge based on the control voltage.

2. The automatic full-scale calibration circuit based on a Pirani vacuum transmitter according to claim 1, characterized in that, The programmable potentiometer is a digital potentiometer of model AD8400.

3. The automatic full-scale calibration circuit based on a Pirani vacuum transmitter according to claim 1, characterized in that, The amplifier U2 is a precision amplifier of model OP777.

4. The automatic full-scale calibration circuit based on a Pirani vacuum transmitter according to claim 1, characterized in that, The transistor Q1 is an 8050 transistor.

5. The automatic full-scale calibration circuit based on a Pirani vacuum transmitter according to claim 1, characterized in that... The automatic full-scale calibration circuit also includes: Resistors R4, R5, R6, R8, R9, R11, capacitor C1, capacitor C2, capacitor C3, diodes D1, D2, and D3; In this configuration, resistor R4 is connected in parallel between the collector and emitter of transistor Q1; resistor R5 is connected between the base of transistor Q1 and the output terminal of amplifier U2; resistor R6 is connected in parallel between the positive input terminal and the positive power supply terminal of amplifier U2; resistor R8 is connected between the common point and the positive input terminal of amplifier U2; resistor R9 is connected in series with capacitor C2; resistor R11 is connected in series with capacitor C3 and then in parallel with capacitor C2; capacitor C2 is connected in parallel with diode D3, and diode D3 is connected in parallel between the negative input terminal and the output terminal of amplifier U2; diode D1 and diode D2 are connected in reverse parallel, with the cathode of diode D1 connected to resistor R8 and the anode of diode D1 connected to resistor R9.

6. An automatic full-scale calibration method based on a Pirani vacuum transmitter, characterized in that, The automatic full-scale calibration circuit based on a Pirani vacuum transmitter as described in any one of claims 1 to 5, wherein the automatic full-scale calibration method comprises the following steps: Acquire the atmospheric pressure signal from the Pirani vacuum transmitter; The stability of the Pirani vacuum transmitter is calibrated by the atmospheric pressure signal. When the Pirani vacuum transmitter reaches a stable state, the filament voltage signal of the Pirani vacuum transmitter is acquired. The calibration factor is obtained through the automatic full-scale calibration circuit, and the calibration level is calculated using the filament voltage signal and the calibration factor. The automatic full-scale calibration circuit performs automatic full-scale calibration according to the calibration level.

7. The automatic full-scale calibration method based on a Pirani vacuum transmitter according to claim 6, characterized in that, The calibration factor is obtained through an automatic full-scale calibration circuit, including the following steps: Write a first set value to the programmable potentiometer in the automatic full-scale calibration circuit, and perform stability calibration on the Pirani vacuum transmitter using the first set value. When the Pirani vacuum transmitter reaches a stable state, record the current pressure signal as the first pressure signal. Write a second set value to the programmable potentiometer, and perform stability calibration on the Pirani vacuum transmitter using the second set value. When the Pirani vacuum transmitter reaches a stable state, record the current pressure signal as the second pressure signal. Calculate the absolute value of the difference between the first pressure signal and the second pressure signal, and use the absolute value of the difference as a calibration factor.

8. The automatic full-scale calibration method based on a Pirani vacuum transmitter according to claim 7, characterized in that, The first setting value and the second setting value are adjacent in magnitude.

9. The automatic full-scale calibration method based on a Pirani vacuum transmitter according to claim 7, characterized in that, Calculating the calibration level using the filament voltage signal and the calibration factor includes: CaliVa = |PresetPa - VacuumPa| / K; where CaliVa is the calibration level, PresetPa is the preset value, VacuumPa is the filament voltage signal, and K is the calibration factor.

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