Alternating current excitation constant temperature electric bridge lock-in amplification vacuum degree detection method

Abstract

The application relates to an AC excitation constant-temperature electric bridge locking amplification vacuum degree detection method, and belongs to the technical field of vacuum degree detection. The method aims at the problem that the existing technology cannot accurately measure the unadjusted voltage of a vacuum gauge electric bridge. The method comprises the following steps: an AC excitation voltage is used as an excitation signal of a constant-temperature electric bridge, and a square wave reference signal in phase with the excitation signal is obtained; when the vacuum degree of a vacuum environment changes, the constant-temperature electric bridge outputs an AC unadjusted voltage signal under the action of the excitation signal, the AC unadjusted voltage signal is amplified through a preamplifier circuit, then a phase-sensitive detector is used to multiply the AC unadjusted voltage signal and the square wave reference signal, the multiplication result is subjected to low-pass filtering to obtain the effective value of the DC voltage of the AC unadjusted voltage signal; then the amplitude of the excitation signal is adjusted according to the change of the effective value of the DC voltage, so that the constant-temperature electric bridge reaches a balanced state; the change of the vacuum degree is determined according to the amplitude change of the excitation signal corresponding to the balanced state of the constant-temperature electric bridge, and the vacuum degree detection is realized. The application is used for measuring the vacuum degree.

Description

Technical Field

[0001] This invention relates to an AC-excited constant-temperature bridge locked amplification vacuum degree detection method, belonging to the field of vacuum degree detection technology. Background Technology

[0002] Currently, resistance vacuum gauges are widely used in the field of low and medium vacuum testing. These gauges typically employ a constant-temperature bridge method to set up the measurement circuit of the resistance vacuum gauge tube. Then, when measuring the bridge offset voltage, a differential amplifier circuit is used to directly amplify the bridge offset voltage signal. However, when the pressure change in the measured environment is small, the bridge offset voltage is easily drowned out by noise, making accurate measurement of the bridge offset voltage impossible. Summary of the Invention

[0003] To address the problem that existing technologies cannot accurately measure the offset voltage of a vacuum gauge bridge, this invention provides an AC-excited, constant-temperature bridge-locked amplified vacuum degree detection method.

[0004] The present invention provides a method for detecting vacuum degree using an AC-excited isothermal bridge-locked amplification system, comprising:

[0005] An AC excitation voltage is used as the excitation signal for a constant-temperature bridge, and a square wave reference signal in phase with the excitation signal is obtained.

[0006] When the vacuum level of the vacuum environment changes, the constant-temperature bridge outputs an AC offset voltage signal under the action of the excitation signal. After being amplified by the preamplifier circuit, it is multiplied by the square wave reference signal using a phase-sensitive detector. The result of the multiplication is filtered by a low-pass filter to obtain the effective value of the DC voltage of the AC offset voltage signal.

[0007] The amplitude of the excitation signal is then adjusted based on the change in the effective value of the DC voltage to bring the constant-temperature bridge to a balanced state. The change in vacuum level is determined based on the change in the amplitude of the excitation signal corresponding to the balanced state of the constant-temperature bridge, thus realizing vacuum level detection.

[0008] According to the AC-excited isothermal bridge-locked amplified vacuum degree detection method of the present invention, the method for generating the excitation signal is as follows:

[0009] A microcontroller is used to control a D / A converter to generate a 0 to +5V sine wave signal, which is then amplified by an operational amplifier and a power amplifier circuit to generate an AC excitation voltage with an amplitude of 12.5V as the excitation signal for a constant-temperature bridge.

[0010] The D / A converter generates a sinusoidal signal and simultaneously outputs a square wave voltage signal; the square wave voltage signal is phase-adjusted by a phase-shifting circuit to obtain a square wave reference signal.

[0011] According to the AC excitation constant-temperature bridge locked amplification vacuum degree detection method of the present invention, the amplitude of the excitation signal is adjusted by a PI controller, and the control parameters of the PI controller are tuned by a relay feedback method.

[0012] According to the AC-excited constant-temperature bridge lock-in amplification vacuum degree detection method of the present invention, the detection system consists of a microcontroller, a signal generation unit composed of a D / A converter, a phase-shifting circuit, an operational amplifier, and a power amplifier circuit, a constant-temperature bridge, and a lock-in amplification unit composed of a preamplifier circuit, a phase-sensitive detector, and a low-pass filter.

[0013] Determining the control parameters of the PI controller includes calculating the critical gain K of the detection system. PC :

[0014]

[0015] In the formula, G0 is the mathematical model of the detection system, ω c Where is the cutoff frequency, N is the ideal relay description function corresponding to the relay feedback method, X is the amplitude of the DC voltage RMS oscillation curve, and M is the amplitude of the ideal relay corresponding to the relay feedback method.

[0016] According to the AC-excited isothermal bridge lock-in amplification vacuum degree detection method of the present invention, based on the ZN table of the critical proportionality method, the critical gain K is used. PC The oscillation period T of the DC voltage RMS oscillation curve C Determine the control parameters of the PI controller:

[0017]

[0018] In the formula K P K is the proportional gain of the PI controller. I This represents the integral coefficient of the PI controller.

[0019] According to the AC-excited constant-temperature bridge locked amplification vacuum degree detection method of the present invention, the effective value of the DC voltage of the AC offset voltage signal is converted into a digital signal by an A / D converter, and the A / D converter controls the sampling time of the effective value of the DC voltage by a T0 timer.

[0020] According to the AC excitation constant-temperature bridge locked amplification vacuum degree detection method of the present invention, the PI controller adjusts the amplitude of the excitation signal according to the change of the effective value of the DC voltage, and outputs a sine table of the excitation signal through the T12 timer. The sine table is output to the D / A converter through the synchronous serial interface, so that the D / A converter generates a sine signal.

[0021] According to the AC-excited isothermal bridge-locked amplified vacuum detection method of the present invention, the relationship between vacuum degree and excitation signal amplitude is as follows:

[0022]

[0023] p = 30000v - 308000, p ∈ (10 3 -10 4 )Pa

[0024] p = 180000v - 1898000, p ∈ (10 4 -10 5 )Pa

[0025] In the formula, p is the vacuum level and v is the amplitude of the excitation signal.

[0026] According to the AC-excited constant-temperature bridge locked amplification vacuum degree detection method of the present invention, the circuit structure of the microcontroller and the signal generation unit composed of a D / A converter, a phase-shifting circuit, and operational and power amplifier circuits is as follows:

[0027] The microcontroller's synchronous serial interface SPI uses a three-wire mode, connecting to the SCLK, / SYNC, and DIN pins of the D / A converter respectively. The VA pin of the D / A converter is connected to the power supply VCC. The VREF1,2 pins of the D / A converter are connected to the Vout2 pin of the reference voltage source. The Vin pin of the reference voltage source is connected to the power supply VCC, and the Gnd pin of the reference voltage source is connected to the power ground. The Vout1 pin of the reference voltage source is connected to the non-inverting input of the first operational amplifier, and the inverting input of the first operational amplifier is connected to its output. A resistor R1 is connected between the output of the first operational amplifier and the inverting input of the second operational amplifier, and a resistor R2 is connected between the inverting input of the second operational amplifier and its output.

[0028] A resistor R3 is connected between the Vout pin of the D / A converter and the non-inverting input of the second operational amplifier, and a resistor R4 is connected between the non-inverting input of the second operational amplifier and the power supply ground. The output of the second operational amplifier is connected to the non-inverting input of the power amplifier, and the inverting input of the power amplifier is connected to its output. The output of the power amplifier outputs an AC excitation voltage as the excitation signal of the constant-temperature bridge.

[0029] The Vout2 pin of the D / A converter outputs a square wave voltage signal. The Vout2 pin of the D / A converter is connected to one end of potentiometer R5. The movable end of potentiometer R5 is connected to the non-inverting input of the third operational amplifier. A capacitor C is connected between the non-inverting input of the third operational amplifier and the power supply ground. The inverting input of the third operational amplifier is connected to its output. The output of the third operational amplifier is connected to the non-inverting input of the comparator. The inverting input of the comparator is connected to the Vout1 pin of the reference voltage source. A resistor R6 is connected between the output of the comparator and the power supply VCC. The output of the comparator outputs a square wave reference signal.

[0030] According to the AC-excited isothermal bridge locked amplification vacuum degree detection method of the present invention, the isothermal bridge is a Wheatstone bridge;

[0031] The input terminal of the Wheatstone bridge is connected to the output terminal of the power amplifier; resistor Rc1 and hot wire resistor Rw form one arm of the Wheatstone bridge, and resistor Rc2 and resistor Rv form the other arm of the Wheatstone bridge. The two arms of the Wheatstone bridge output AC offset voltage signals.

[0032] The circuit structure of the lock-in amplifier unit, consisting of a preamplifier circuit, a phase-sensitive detector, and a low-pass filter, is as follows:

[0033] A resistor R7 is connected between the negative reference terminal of the AC offset voltage signal and the non-inverting input terminal of the fourth op-amp; a resistor R9 is connected between the inverting input terminal and the output terminal of the fourth op-amp; a resistor R8 is connected between the positive reference terminal of the AC offset voltage signal and the non-inverting input terminal of the fifth op-amp; a resistor R11 is connected between the inverting input terminal of the fifth op-amp and the inverting input terminal of the fourth op-amp; a resistor R12 is connected between the inverting input terminal and the output terminal of the fifth op-amp; a resistor R13 is connected between the output terminal of the fifth op-amp and the non-inverting input terminal of the sixth op-amp; and a resistor R10 is connected between the output terminal of the fourth op-amp and the inverting input terminal of the sixth op-amp.

[0034] A resistor R15 is connected between the non-inverting input terminal of the sixth op-amp and the power supply ground; a resistor R14 is connected between the inverting input terminal and the output terminal of the sixth op-amp; the output terminal of the sixth op-amp outputs a non-inverting signal and is connected to the Ax terminal of the phase-sensitive detector.

[0035] A resistor R17 is connected between the output of the sixth op-amp and the inverting input of the seventh op-amp; a resistor R18 is connected between the inverting input and the output of the seventh op-amp; and a resistor R16 is connected between the non-inverting input and the power supply ground of the seventh op-amp. The output of the seventh op-amp outputs an inverted signal and is connected to the Ay terminal of the phase-sensitive detector.

[0036] The phase-sensitive detector is implemented using a digitally controlled analog switch CD4053; the S0 terminal of the phase-sensitive detector is connected to a square wave reference signal; the output terminal of the phase-sensitive detector is connected to the input terminal of a low-pass filter, and the output terminal of the low-pass filter outputs the effective value of the DC voltage of the AC offset voltage signal.

[0037] The beneficial effects of the present invention are as follows: The method of the present invention can extract a precise AC offset voltage signal through lock-in amplification technology, thereby achieving the purpose of accurately measuring the vacuum degree.

[0038] The method of this invention applies lock-in amplification technology to vacuum detection, and to adapt to lock-in amplification technology, an AC excitation voltage is used as the excitation signal of a constant-temperature bridge, which enables the constant-temperature bridge to directly generate an AC offset voltage signal.

[0039] Experiments have verified that the method of the present invention is effective in 10... -1 -10 3 Within the main measurement range of Pa, the maximum measurement error was 15%. Noise was effectively filtered out from the extracted AC offset voltage signal, and the results of multiple experiments were consistent. Attached Figure Description

[0040] Figure 1 This is an overall flowchart of the AC-excited constant-temperature bridge locked amplified vacuum degree detection method described in this invention;

[0041] Figure 2 It is a circuit structure diagram of a microcontroller, D / A converter, operational amplifier, and power amplifier circuit;

[0042] Figure 3 This is the circuit structure diagram of the phase-shifting circuit;

[0043] Figure 4 This is the circuit diagram of a Wheatstone bridge;

[0044] Figure 5 This is a circuit diagram of a lock-in amplifier unit consisting of a preamplifier circuit, a phase-sensitive detector, and a low-pass filter.

[0045] Figure 6 This is a schematic diagram of the sinusoidal signal generated by the D / A converter and the AC excitation voltage;

[0046] Figure 7 This is a diagram of the square wave voltage signal generated by the D / A converter and the square wave reference signal after phase shifting;

[0047] Figure 8 This is the output waveform of the phase-sensitive detector;

[0048] Figure 9 It is a constant-amplitude oscillation curve of the DC voltage RMS value of the AC offset voltage signal;

[0049] Figure 10 This is a flowchart of the software implementation of the method of the present invention. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0052] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0053] Specific Implementation Method 1: Combination Figures 1 to 5 As shown, this invention provides a method for detecting vacuum degree using an AC-excited isothermal bridge-locked amplification system, comprising:

[0054] An AC excitation voltage is used as the excitation signal for a constant-temperature bridge, and a square wave reference signal in phase with the excitation signal is obtained.

[0055] When the vacuum level of the vacuum environment changes, the constant-temperature bridge outputs an AC offset voltage signal under the action of the excitation signal. After being amplified by the preamplifier circuit, it is multiplied by the square wave reference signal using a phase-sensitive detector. The result of the multiplication is filtered by a low-pass filter to obtain the effective value of the DC voltage of the AC offset voltage signal.

[0056] The amplitude of the excitation signal is then adjusted based on the change in the effective value of the DC voltage to bring the constant-temperature bridge to a balanced state. The change in vacuum level is determined based on the change in the amplitude of the excitation signal corresponding to the balanced state of the constant-temperature bridge, thus realizing vacuum level detection.

[0057] The steady-state value of the AC offset voltage signal output by the constant-temperature bridge is zero. When a deviation occurs, it may be positive or negative. Negative values ​​cannot be directly processed by the microcontroller. Therefore, the AC offset voltage signal is first processed by the voltage boost circuit, i.e., the lock-in amplifier unit, before entering the microcontroller for processing.

[0058] Furthermore, combined with Figure 1 and Figure 2 As shown, the method for generating the excitation signal is as follows:

[0059] A microcontroller is used to control a D / A converter to generate a sine wave signal of 0 to +5V. The signal is then passed through a subsequent operational amplifier and power amplifier circuit to generate an AC excitation voltage Vin with an amplitude of 12.5V, which serves as the excitation signal for a constant-temperature bridge.

[0060] The D / A converter generates a sinusoidal signal and simultaneously outputs a square wave voltage signal; the square wave voltage signal is phase-adjusted by a phase-shifting circuit to obtain a square wave reference signal.

[0061] In this embodiment, a sine wave signal and a square wave signal with an amplitude of 0 to +5V are output via a D / A converter. The sine wave signal is converted into an excitation signal with an amplitude of 12.5V by an operational amplifier and a power amplifier circuit. To ensure synchronization between the square wave signal and the AC offset voltage signal, a phase-shifting circuit is added to adjust the phase of the square wave signal. This embodiment uses an AC excitation signal to excite the bridge circuit, making it a carrier signal, causing the bridge circuit to output an AC offset voltage, which enters the lock-in amplification unit. In the lock-in amplification unit, it is first initially amplified by an instrumentation amplifier, and then multiplied by a square wave reference signal by a phase-sensitive detector. At this time, the DC effective value of the AC offset voltage is in the output of the phase-sensitive detector, while the interference signal is filtered out after low-pass filtering. Then, the DC effective value of the offset voltage is acquired by the A / D converter of the microcontroller, and the amplitude of the excitation signal is controlled to make the bridge circuit rebalanced.

[0062] As an example, the microcontroller could be an XC866 microcontroller.

[0063] As an example, a D / A converter can be implemented using the DAC128S085 chip.

[0064] Combined Figure 1 As shown, the amplitude of the excitation signal is adjusted using a PI controller, and the control parameters of the PI controller are tuned using a relay feedback method. Its software flow can be combined with... Figure 10 The process shown is implemented.

[0065] Figure 10 In this system, under constant vacuum detection conditions, the amplitude of the excitation signal is adjusted using a PI controller. When the vacuum detection conditions change, the PI controller enters a self-tuning mode based on relay feedback. When the selector switch k=1, after the relay feedback output, the system waits for the self-excited oscillation of the detection system to stabilize, and then updates the PI coefficients of the PI controller accordingly. After entering PI control, the amplitude of the excitation signal is changed by scaling the data from the sine wave table based on the DC effective value of the offset voltage, and the vacuum level is obtained and displayed based on the amplitude of the excitation signal.

[0066] In this embodiment, the amplitude of the excitation signal is variable, which can be achieved by scaling the digital input to the D / A converter using a corresponding conversion module. The output waveform is as follows: Figure 6 As shown.

[0067] The D / A converter can also generate a square wave whose phase is synchronized with the excitation signal, which is used to lock the phase-sensitive detector in the amplification stage. To ensure that the square wave reference signal is synchronized with the AC offset voltage signal, a phase-shifting circuit is added to control the phase of the square wave reference signal, and the output waveform is as follows: Figure 7 As shown.

[0068] In this embodiment, a PI control law is used to control the system. The detection system is a nonlinear control system, which is difficult to describe directly using a transfer function; that is, the transfer function of the controlled object is unknown. The controller parameters are obtained by tuning using a relay feedback method, which is an improvement on the ZN critical proportional gain method. The specific steps are as follows:

[0069] 1) First, the detection system is made to oscillate by adjusting the excitation signal. The oscillation process is as follows: when the feedback is less than the expected value, the maximum positive control quantity is output; when the feedback is greater than the expected value, the minimum negative control quantity is output, causing the system to oscillate forcibly. The relay outputs a control signal for the amplitude of the excitation signal, which serves as the input signal for controlling the amplitude of the excitation signal of the D / A converter. In this embodiment, the amplitude of the excitation signal cannot be negative, so the amplitude of the excitation signal corresponding to the set value is superimposed with an upper and lower deviation signal amplitude M.

[0070] 2) Start the system and bring the vacuum level of the vacuum environment to the set value. Record the waveform of the effective value of the offset DC voltage output at this time, such as... Figure 9 As shown, by utilizing the signal A / D conversion and signal capture functions within the microcontroller, the amplitude X and oscillation period T of the DC voltage RMS oscillation curve are obtained. C Based on the measured oscillation amplitude during system oscillation, the critical gain K of the detection system is calculated. PC .

[0071] Furthermore, combining Figure 1 and Figure 2 As shown, the detection system consists of a microcontroller, a signal generation unit composed of a D / A converter, a phase shift circuit, an operational amplifier, and a power amplifier circuit, a constant-temperature bridge, and a lock-in amplifier unit composed of a preamplifier circuit, a phase-sensitive detector, and a low-pass filter.

[0072] Determining the control parameters of the PI controller includes calculating the critical gain K of the detection system. PC :

[0073]

[0074] In the formula, G0 is the mathematical model of the detection system, ω c Where is the cutoff frequency, N is the ideal relay description function corresponding to the relay feedback method, X is the amplitude of the DC voltage RMS oscillation curve, and M is the amplitude of the ideal relay corresponding to the relay feedback method.

[0075] In this embodiment, K PC With T C The ZN table based on the critical proportionality method is derived from the critical gain K. PC The oscillation period T of the DC voltage RMS oscillation curve CDetermine the control parameters of the PI controller:

[0076]

[0077] In the formula K P K is the proportional gain of the PI controller. I The integral coefficient of the PI controller.

[0078] By fine-tuning the calculated parameters, satisfactory control results can be obtained.

[0079] Combination Figure 1 As shown, the effective value of the DC voltage of the AC offset voltage signal is converted into a digital signal by a 10-bit A / D converter built into the microcontroller. The A / D converter controls the sampling time of the effective value of the DC voltage through a timer T0.

[0080] The PI controller adjusts the amplitude of the excitation signal according to the change of the effective value of the DC voltage, and outputs a sine table of the excitation signal through the T12 timer. The sine table is output to the D / A converter through the synchronous serial interface, so that the D / A converter generates a sine signal.

[0081] Furthermore, the amplitude of the excitation voltage is adjusted according to the magnitude of the AC offset voltage signal, so that the bridge can be rebalanced.

[0082] After calibration, the relationship between the vacuum level and the excitation signal amplitude can be obtained through fitting as follows:

[0083]

[0084] p = 30000v - 308000, p ∈ (10 3 -10 4 )Pa

[0085] p = 180000v - 1898000, p ∈ (10 4 -10 5 )Pa

[0086] In the formula, p is the vacuum level and v is the amplitude of the excitation signal.

[0087] The vacuum level measured in this embodiment can be displayed using a digital tube, and the digital tube is controlled to light up by communicating with the shift chip through the serial interface of the microcontroller.

[0088] Combination Figures 1 to 3 As shown, the circuit structure of the microcontroller and the signal generation unit, which consists of a D / A converter, a phase shift circuit, and operational and power amplifier circuits, is as follows:

[0089] The microcontroller's synchronous serial interface SPI uses a three-wire mode, connecting to the SCLK, / SYNC, and DIN pins of the D / A converter respectively. The VA pin of the D / A converter is connected to the power supply VCC. The VREF1,2 pins of the D / A converter are connected to the Vout2 pin of the reference voltage source. The Vin pin of the reference voltage source is connected to the power supply VCC, and the Gnd pin of the reference voltage source is connected to the power ground. The Vout1 pin of the reference voltage source is connected to the non-inverting input of the first operational amplifier, and the inverting input of the first operational amplifier is connected to its output. A resistor R1 is connected between the output of the first operational amplifier and the inverting input of the second operational amplifier, and a resistor R2 is connected between the inverting input of the second operational amplifier and its output.

[0090] A resistor R3 is connected between the Vout pin of the D / A converter and the non-inverting input of the second operational amplifier, and a resistor R4 is connected between the non-inverting input of the second operational amplifier and the power supply ground. The output of the second operational amplifier is connected to the non-inverting input of the power amplifier, and the inverting input of the power amplifier is connected to its output. The output of the power amplifier outputs an AC excitation voltage as the excitation signal of the constant-temperature bridge.

[0091] The Vout2 pin of the D / A converter outputs a square wave voltage signal. The Vout2 pin of the D / A converter is connected to one end of potentiometer R5. The movable end of potentiometer R5 is connected to the non-inverting input of the third operational amplifier. A capacitor C is connected between the non-inverting input of the third operational amplifier and the power supply ground. The inverting input of the third operational amplifier is connected to its output. The output of the third operational amplifier is connected to the non-inverting input of the comparator. The inverting input of the comparator is connected to the Vout1 pin of the reference voltage source. A resistor R6 is connected between the output of the comparator and the power supply VCC. The output of the comparator outputs a square wave reference signal.

[0092] In this embodiment, the first operational amplifier outputs a 2.5V DC voltage as a voltage follower. In the second operational amplifier, it performs operations with the sinusoidal signal output by the D / A converter, causing the 0-5V sinusoidal signal to be shifted down by 2.5V and amplified by 5 times, converting it into a sinusoidal signal with an amplitude of 12.5. Then, the power is increased by the power amplifier, making it an excitation signal that can excite the bridge circuit.

[0093] Figure 3 In the process, the square wave voltage signal is filtered by RC(R5,C) and then phase lags. The comparator is used to convert the lag waveform into a square wave reference signal.

[0094] Combination Figure 1 , Figure 4 and Figure 5 As shown, the constant-temperature bridge is a Wheatstone bridge;

[0095] The input terminal of the Wheatstone bridge is connected to the output terminal of the power amplifier; resistor Rc1 and hot wire resistor Rw form one arm of the Wheatstone bridge, and resistor Rc2 and resistor Rv form the other arm of the Wheatstone bridge. The two arms of the Wheatstone bridge output AC offset voltage signals.

[0096] The circuit structure of the lock-in amplifier unit, consisting of a preamplifier circuit, a phase-sensitive detector, and a low-pass filter, is as follows:

[0097] A resistor R7 is connected between the negative reference terminal of the AC offset voltage signal and the non-inverting input terminal of the fourth op-amp; a resistor R9 is connected between the inverting input terminal and the output terminal of the fourth op-amp; a resistor R8 is connected between the positive reference terminal of the AC offset voltage signal and the non-inverting input terminal of the fifth op-amp; a resistor R11 is connected between the inverting input terminal of the fifth op-amp and the inverting input terminal of the fourth op-amp; a resistor R12 is connected between the inverting input terminal and the output terminal of the fifth op-amp; a resistor R13 is connected between the output terminal of the fifth op-amp and the non-inverting input terminal of the sixth op-amp; and a resistor R10 is connected between the output terminal of the fourth op-amp and the inverting input terminal of the sixth op-amp.

[0098] A resistor R15 is connected between the non-inverting input terminal of the sixth op-amp and the power supply ground; a resistor R14 is connected between the inverting input terminal and the output terminal of the sixth op-amp; the output terminal of the sixth op-amp outputs a non-inverting signal and is connected to the Ax terminal of the phase-sensitive detector.

[0099] A resistor R17 is connected between the output of the sixth op-amp and the inverting input of the seventh op-amp; a resistor R18 is connected between the inverting input and the output of the seventh op-amp; and a resistor R16 is connected between the non-inverting input and the power supply ground of the seventh op-amp. The output of the seventh op-amp outputs an inverted signal and is connected to the Ay terminal of the phase-sensitive detector.

[0100] The phase-sensitive detector is implemented using a digitally controlled analog switch CD4053. The S0 terminal of the phase-sensitive detector is connected to a square wave reference signal. The output terminal of the phase-sensitive detector is connected to the input terminal of a low-pass filter, and the output terminal of the low-pass filter outputs the DC effective value Q of the AC offset voltage signal. After passing through the low-pass filter, the DC effective value of the AC offset voltage is preserved, while the interference signal is filtered out as a high-frequency signal.

[0101] The phase-sensitive detector receives an AC offset voltage signal at its Ax terminal and an inverted AC offset voltage signal at its Ay terminal. A square wave reference signal controls the on / off state of the two channels, Ax and Ay, via a digitally controlled analog switch CD4053. The phase-sensitive detector multiplies the square wave reference signal by the AC offset voltage signal; that is, when the square wave reference signal output is 1, the Ax terminal outputs, and when the square wave reference signal output is 0, the Ay terminal outputs.

[0102] When the vacuum level of the detection environment changes, the temperature of the resistance gauge changes, thus altering its resistance. This causes the previously balanced bridge circuit to become unbalanced, generating an AC offset voltage ΔV. The AC offset voltage ΔV is first amplified by a preamplifier circuit, then enters the core of the latch-up amplification section—the phase-sensitive detector. This phase-sensitive detector uses an electronic switch-type phase-sensitive detector, implemented by a digitally controlled analog switch CD4053. After passing through a low-pass filter, the effective DC voltage value of the AC offset voltage is obtained. The output waveform is as follows: Figure 8 As shown, from top to bottom, the waveforms are: positive AC offset voltage, AC offset voltage after inversion, square wave reference signal, and output waveform of phase-sensitive detector.

[0103] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for detecting vacuum degree by AC-excited isothermal bridge locking amplification, characterized in that... include, An AC excitation voltage is used as the excitation signal for a constant-temperature bridge, and a square wave reference signal in phase with the excitation signal is obtained. When the vacuum level of the vacuum environment changes, the constant-temperature bridge outputs an AC offset voltage signal under the action of the excitation signal. After being amplified by the preamplifier circuit, it is multiplied by the square wave reference signal using a phase-sensitive detector. The result of the multiplication is filtered by a low-pass filter to obtain the effective value of the DC voltage of the AC offset voltage signal. The amplitude of the excitation signal is then adjusted based on the change in the effective value of the DC voltage to bring the constant-temperature bridge to a balanced state. The change in vacuum level is determined based on the change in the amplitude of the excitation signal corresponding to the balanced state of the constant-temperature bridge, thus realizing vacuum level detection. The method for generating the excitation signal is as follows: A microcontroller is used to control a D / A converter to generate a 0~+5V sinusoidal signal, which is then amplified by operational amplifier and power amplifier circuits to generate an AC excitation voltage with an amplitude of 12.5V as the excitation signal for a constant-temperature bridge. The D / A converter generates a sinusoidal signal and simultaneously outputs a square wave voltage signal; the square wave voltage signal is phase-adjusted by a phase-shifting circuit to obtain a square wave reference signal. The amplitude of the excitation signal is adjusted using a PI controller, and the control parameters of the PI controller are tuned using a relay feedback method. The detection system consists of a microcontroller, a signal generation unit composed of a D / A converter, a phase shifter circuit, an operational amplifier, and a power amplifier circuit, a constant-temperature bridge, and a lock-in amplifier unit composed of a preamplifier circuit, a phase-sensitive detector, and a low-pass filter. Determining the control parameters of the PI controller includes calculating the critical gain of the detection system. : ， In the formula For the mathematical model of the detection system, For the cutoff frequency, This is the description function of the ideal relay corresponding to the relay feedback method. The amplitude of the DC voltage RMS oscillation curve. This represents the amplitude of the ideal relay corresponding to the relay feedback method; ZN tables based on the critical proportionality method, derived from critical gain The oscillation period of the DC voltage RMS oscillation curve Determine the control parameters of the PI controller: ； In the formula The proportional gain of the PI controller. The integral coefficient of the PI controller; The PI controller adjusts the amplitude of the excitation signal according to the change of the effective value of the DC voltage, and outputs a sine table of the excitation signal through the T12 timer. The sine table is output to the D / A converter through the synchronous serial interface, so that the D / A converter generates a sine signal. The relationship between vacuum level and excitation signal amplitude is as follows: ， ， In the formula For vacuum degree, This represents the amplitude of the excitation signal.

2. The AC-excited isothermal bridge-locked amplified vacuum degree detection method according to claim 1, characterized in that, The effective value of the DC voltage of the AC offset voltage signal is converted into a digital signal by an A / D converter, and the sampling time of the effective value of the DC voltage is controlled by a timer T0.

3. The AC-excited isothermal bridge-locked amplified vacuum degree detection method according to claim 1, characterized in that, The circuit structure of the microcontroller and the signal generation unit, which consists of a D / A converter, a phase shifter, an operational amplifier, and a power amplifier, is as follows: The microcontroller's synchronous serial interface SPI uses a three-wire mode, connecting to the SCLK, SYNC, and DIN pins of the D / A converter respectively. The VA pin of the D / A converter is connected to the power supply VCC. The VREF1 and 2 pins of the D / A converter are connected to the Vout2 pin of the reference voltage source. The Vin pin of the reference voltage source is connected to the power supply VCC, and the Gnd pin of the reference voltage source is connected to the power supply ground. The Vout1 pin of the reference voltage source is connected to the non-inverting input of the first operational amplifier, and the inverting input of the first operational amplifier is connected to its output. A resistor R1 is connected between the output terminal of the first operational amplifier and the inverting input terminal of the second operational amplifier, and a resistor R2 is connected between the inverting input terminal of the second operational amplifier and its output terminal. A resistor R3 is connected between the Vout pin of the D / A converter and the non-inverting input of the second operational amplifier, and a resistor R4 is connected between the non-inverting input of the second operational amplifier and the power supply ground. The output of the second operational amplifier is connected to the non-inverting input of the power amplifier, and the inverting input of the power amplifier is connected to its output. The output of the power amplifier outputs an AC excitation voltage as the excitation signal of the constant-temperature bridge. The Vout2 pin of the D / A converter outputs a square wave voltage signal. The Vout2 pin of the D / A converter is connected to one end of potentiometer R5. The moving end of potentiometer R5 is connected to the non-inverting input of the third operational amplifier. A capacitor C is connected between the non-inverting input of the third operational amplifier and the power supply ground. The inverting input of the third operational amplifier is connected to its output. The output of the third operational amplifier is connected to the non-inverting input of the comparator, the inverting input of the comparator is connected to the Vout1 pin of the reference voltage source, and a resistor R6 is connected between the output of the comparator and the power supply VCC; the output of the comparator outputs a square wave reference signal.

4. The AC-excited isothermal bridge locked amplification vacuum degree detection method according to claim 1, characterized in that, The constant-temperature bridge is a Wheatstone bridge; The input terminal of the Wheatstone bridge is connected to the output terminal of the power amplifier; resistor Rc1 and hot wire resistor Rw form one arm of the Wheatstone bridge, and resistor Rc2 and resistor Rv form the other arm of the Wheatstone bridge. The two arms of the Wheatstone bridge output AC offset voltage signals. The circuit structure of the lock-in amplifier unit, consisting of a preamplifier circuit, a phase-sensitive detector, and a low-pass filter, is as follows: A resistor R7 is connected between the negative reference terminal of the AC offset voltage signal and the non-inverting input terminal of the fourth op-amp; a resistor R9 is connected between the inverting input terminal and the output terminal of the fourth op-amp; a resistor R8 is connected between the positive reference terminal of the AC offset voltage signal and the non-inverting input terminal of the fifth op-amp; a resistor R11 is connected between the inverting input terminal of the fifth op-amp and the inverting input terminal of the fourth op-amp; a resistor R12 is connected between the inverting input terminal and the output terminal of the fifth op-amp; a resistor R13 is connected between the output terminal of the fifth op-amp and the non-inverting input terminal of the sixth op-amp; and a resistor R10 is connected between the output terminal of the fourth op-amp and the inverting input terminal of the sixth op-amp. A resistor R15 is connected between the non-inverting input terminal of the sixth op-amp and the power supply ground; a resistor R14 is connected between the inverting input terminal and the output terminal of the sixth op-amp; the output terminal of the sixth op-amp outputs a non-inverting signal and is connected to the Ax terminal of the phase-sensitive detector. A resistor R17 is connected between the output of the sixth op-amp and the inverting input of the seventh op-amp; a resistor R18 is connected between the inverting input and the output of the seventh op-amp; and a resistor R16 is connected between the non-inverting input and the power supply ground of the seventh op-amp. The output of the seventh op-amp outputs an inverted signal and is connected to the Ay terminal of the phase-sensitive detector. The phase-sensitive detector is implemented using a digitally controlled analog switch CD4053; The S0 terminal of the phase-sensitive detector is connected to a square wave reference signal; the output terminal of the phase-sensitive detector is connected to the input terminal of a low-pass filter, and the output terminal of the low-pass filter outputs the effective value of the DC voltage of the AC offset voltage signal.

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