A high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell

Abstract

The application discloses a high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell, which is used for detecting fault characteristic gases such as acetylene in oil-immersed transformer insulating oil. The degassing section performs actions such as ultrasonic cavitation, piston air pulling, low-frequency vibration and the like under the constraint of a threshold value in the quantitative oil sample and the known headspace volume, and the next action is adaptively selected according to the newly released gas molar number and the marginal gas release amount. The endpoint is determined through constant-volume isolation window measurement, gas collection and homogenization cavity transfer and gas collection amount closed criterion. The gas distribution and photoacoustic detection section isochorically divides the same batch of homogenized gas, forms sample gas and reference gas of the same cycle through a matrix matching blank cylinder and a target gas consumption cylinder, and alternately enters a first double-channel resonant photoacoustic cell and a second double-channel resonant photoacoustic cell under the interchange of four-way reversing valve A / B valve positions. The same laser is split to irradiate, the sound-electricity is normalized, the roles are interchanged, the target gas molar fraction is double-difference inversed, and then the oil concentration is obtained through mass balance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dissolved gas analysis and photoacoustic spectroscopy in insulating oil, in particular to a high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell. BACKGROUND

[0002] When partial discharge, spark discharge, arc discharge or overheating occurs inside an oil-immersed transformer, characteristic gases such as hydrogen, methane, acetylene, ethylene, ethane, carbon monoxide and carbon dioxide are generated, among which acetylene has a high indication significance for discharge faults. Online detection usually releases the gas from the insulating oil first, and then uses chromatographic or spectroscopic methods for detection. Pretreatment and detection are not independent of each other: the volume of the oil sample, the headspace volume, the degassing pressure, the temperature and the degassing completion degree will all directly change the concentration of the target gas entering the detection unit.

[0003] The prior art has disclosed vacuum or ultrasonic degassing, piston vacuum spraying, differential resonant photoacoustic cell and modulation frequency tracking: such as the patent with publication number CN115201116B which discloses a scheme using an excitation cavity and a compensation cavity, two light sources and two microphones for differential; such as the patent with publication number CN109765181B which discloses a differential resonant photoacoustic cell, which realizes effective isolation of the measured gas and the acoustic-electric converter by combining differential and resonant structures; and finally such as the patent with publication number CN120507295A which discloses a micro differential cylinder-cone composite photoacoustic cell, the cylinder-cone composite structure of the photoacoustic cell resonantly amplifies the photoacoustic signal while suppressing common-mode noise, thereby improving the signal-to-noise ratio.

[0004] However, the above-mentioned existing schemes or combinations still have three types of interrelated problems: ① Fixed degassing time cannot give the actual release amount of this period, resulting in a lack of traceable amount of substance input for subsequent oil concentration inversion; ② If the sample gas and the reference come from different batches, different fillers or one side is not exposed to light, oil vapor, water vapor, flow resistance, window absorption and fixed channel gain will all enter the difference, making it difficult to determine whether the difference is caused only by acetylene; ③ Self-checking with standard electrical signals or sound generators can only verify the acoustic-electric link, but cannot verify the acetylene absorption, laser wavelength and photoacoustic conversion link. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell to solve the above problems.

[0006] To achieve the above purpose, the present application realizes the following technical solutions.

[0007] A high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell, comprising: With volume A quantitative oil sample is fed into the sealed degassing chamber through the inlet at the bottom of the chamber and kept at a constant temperature, forming an effective volume of [missing information] above the oil sample. Top headspace; Each vacuum degassing action is numbered k according to its execution time, where k is a positive integer. After the kth vacuum degassing action is completed, the inlet valve, return valve, vacuum valve, and gas collecting valve are closed to form the kth constant-volume isolation window. The absolute pressure of the top headspace is collected at the start and end times of this window. Thermodynamic temperature and compressibility factor Calculate the number of newly released moles corresponding to the k-th vacuum-assisted degassing action. and marginal gas release per unit time and will Benefits of candidate actions Used to select the (k+1)th vacuum-assisted degassing action until the degassing is completed. The endpoint condition is continuously satisfied; After each measurement at the constant volume isolation window is completed, the corresponding incremental gas is transferred through the gas collection port at the top of the sealed degassing chamber to a pre-evacuated chamber with an effective volume of V. b After the gas collection and homogenization chamber is completed, the gas collection valve is closed before the next vacuum degassing action is allowed; After the degassing endpoint, the pressure in the gas collection and homogenization chamber is used as a guide. ,temperature Compression factor The total number of moles of gas collected was obtained. and will and relative deviation As a criterion for gas collection closure, only when If the sample passes the test, the homogenized gas is allowed to proceed to subsequent tests. Simultaneously, the first and second metering loops are filled with homogenized gas from the same batch that has passed through a closed loop. The gas in the first metering loop passes through a matrix-matched blank cylinder to form a sample gas S containing the target gas. The gas in the second metering loop passes through a target gas depletion cylinder to form a target gas residual ratio of [missing value]. The reference gas R is used, and a pairing error is formed based on the pressure, temperature, and volumetric flow rate of S and R before they enter the cavity. ; In valve position A of the four-way reversing valve, S enters the first photoacoustic cavity and R enters the second photoacoustic cavity; in valve position B, R enters the first photoacoustic cavity and S enters the second photoacoustic cavity. The first photoacoustic cavity and the second photoacoustic cavity are both illuminated by the same semiconductor laser beam splitting. The first microphone and the second microphone are respectively located at the sound pressure level of the first photoacoustic cavity and the second photoacoustic cavity. The first micro-sound generator and the second micro-sound generator are respectively located on the cavity wall adjacent to the corresponding microphone. The first optical power monitor and the second optical power monitor are respectively located after the exit window of the two photoacoustic cavities. The complex transfer coefficients of the first and second acoustic-electric channels were obtained using two miniature sound generators. The second harmonic complex signals of valve positions A and B are obtained using two microphones. , and by Normalization ,in ; The difference between the channel values ​​of the two valve positions is subtracted again to obtain the role-swap double difference component. ,according to Target spectral line calibration coefficients Average laser power P of the two channels L The quality factor Q obtained from the frequency sweep in this period is used to invert the mole fraction of the target gas in the homogenized gas. ; Will The target gas solubility coefficient and the final state pressure of the last qualified constant volume isolation window. Substituting into the mass balance yields the target gas concentration in the oil sample. And only in When the self-test of the acoustic and electrical channels, resonance tracking, and zero-point retest all pass, output... And a testing certificate containing all the preceding parameters and results.

[0008] Preferably, the oil sample volume The effective headspace volume is 80–150 mL. The sample volume is 15–40 mL, and the oil sample temperature is [not specified]. The temperature is 40–55°C, and the absolute pressure during the kth vacuum degassing action is 5–25 kPa; the effective volume of the sealed degassing chamber in the kth constant-volume isolation window remains unchanged, and the start and end states of this window are correlated with the type and duration of the kth vacuum degassing action. and motion energy consumption Binding storage.

[0009] Preferably, the vacuum-assisted degassing action includes at least one of piston expansion, vacuum spraying, stirring, and low-frequency vibration, and an ultrasonic pulse of 20–40 kHz, 10–80 W, and 5–45 s can be executed before the action; the cavitation intensity is defined as the ratio of 100–500 kHz broadband cavitation energy to the 20–80 kHz fundamental frequency and low-order harmonic energy. Only the nucleation threshold calibrated on blank oil samples With the risk threshold of pyrolysis The ultrasonic pulses are allowed between them.

[0010] Preferably, the number of newly released moles in the k-th vacuum-assisted degassing action according to Calculate the marginal gas release per unit time. The action benefit B of candidate action a a The controller selects candidate action B from those that meet the requirements of pressure, level, temperature, and cavitation safety window, by using the weighted sum of the predicted gas release amount, predicted action time, and predicted action energy consumption for the candidate action. a The largest action is the (k+1)th vacuum-assisted degassing action.

[0011] Preferred degassing completion indicators Pick The ratio of pressure recovery rate to its threshold and The maximum value among the ratios to the stability threshold; Degassing was stopped after at least two consecutive tests with a value not exceeding 1; total number of moles of gas collected. Relative deviation of gas collection closure , If the gas volume is not greater than the preset upper limit, a degassing-gathering certificate is generated and gas mixing within the same batch is allowed; otherwise, a leak check is performed, gas is re-gathered, and the original gas is not reused. .

[0012] Preferably, the paired gas path modules of the same batch are set between the gas collection and equalization chamber and the first and second photoacoustic chambers, and sequentially include an inlet valve, a first metering ring and a second metering ring, a matrix matching blank cylinder and a target gas depletion cylinder arranged in parallel, a pressure equalization valve, a four-way reversing valve, and an exhaust flushing manifold connected to the outlet of the two photoacoustic chambers along the airflow direction; the matrix matching blank cylinder and the target gas depletion cylinder have the same carrier, geometric dimensions, filling amount and flow resistance, the target gas depletion cylinder retains the target gas selective active site, and the corresponding active site of the matrix matching blank cylinder is passivated.

[0013] Preferably, the target gas residual ratio The calibration value using standard gas is no greater than 0.05; the pairing error between sample gas S and reference gas R is... ,in and The pressure, temperature, and volumetric flow rate data are collected by pressure, temperature, and volumetric flow rate sensors located in the two upstream branches of the four-way directional valve, respectively. If the value is greater than 1, the role swap double difference will not be performed and the gas will be re-matched.

[0014] Preferably, when the laser optical path is closed, and both the first and second photoacoustic cavities are filled with target dissipation gas and isolated from the paired gas path, the same standard electrical signal is input to the first and second micro-generators to obtain the complex transfer coefficient G of the first and second acoustic-electric channels at the actual resonant frequency. j ac and with G j ac The subsequent photoacoustic complex signal is normalized; the self-test is only used to determine whether the transmission link of the first microphone, the second microphone, the dual-channel preamplifier, the phase-locked demodulator and the acoustic cavity has drifted, and does not replace the calibration of the target gas standard gas concentration.

[0015] Preferably, the resonant frequency is predicted based on the cavity temperature, equivalent molar mass of the gas, specific heat ratio, and thermal expansion of the cavity in the first and second photoacoustic cavities. ,exist The system performs coarse and fine frequency sweeps, updating the modulation frequency based on the phase error of the second harmonic complex signal obtained from the first and second microphones. The quality factor Q is calculated from the half-power bandwidth of the frequency sweep in this cycle; Q and Q respectively enter subsequent phase-locked demodulation and Inversion.

[0016] Preferably, the semiconductor laser is a distributed feedback semiconductor laser in the 1510–1540 nm wavelength band, with a laser temperature control error of no more than ±0.01℃ and a drive current ripple of no more than 0.01% of full scale; the target absorption line is scanned with a triangular wave at a frequency of 0.05–0.5 Hz. The sinusoidal wave is used for wavelength modulation, and second harmonic phase-locked demodulation is performed with an integration time of 0.5–3 s. The average laser power of the two paths is formed by the readings of the first and second optical power monitors. .

[0017] Preferred, role-swap double difference components Mole fraction of target gas in homogenized gas Target gas concentration in oil sample ;in The output only enters Inversion, The output is only related to They collectively enter into oil quality equilibrium.

[0018] Preferably, when the gas relay's light gas contact activates, the accumulated free gas volume reaches a threshold, or the gas production rate reaches a threshold, the free gas is sent to the paired gas circuit module of the same batch for rapid detection via the safety gas collection interface and the oil mist removal branch without altering the protection trip circuit, and then the oil sample vacuum degassing detection is initiated; the free gas detection results are converted into equivalent concentration in the oil based on its sampling volume, temperature, and pressure. Then, with The consistency index is formed by the time difference between the two samplings.

[0019] A high-precision rapid detection system for implementing a high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell includes a quantitative oil sampling and return unit, a composite vacuum degassing module, a vacuum source, a gas collection and homogenization chamber, a batch-paired gas path module, a dual-channel resonant photoacoustic module, and a controller. The quantitative oil sampling and return unit is connected to the lower oil inlet of the composite vacuum degassing module via an oil inlet valve and to its lower oil return port via a return valve. The top vacuum port of the composite vacuum degassing module is connected to the vacuum source via a vacuum valve, and the top gas collection port is connected to the gas collection and homogenization chamber via a gas collection valve. A pressure sensor is installed on the top headspace sidewall, a temperature sensor is immersed in the oil sample, and an acoustic emission sensor is installed near the gas-liquid interface adjacent to the chamber wall. The outlet of the gas collection and homogenization chamber is sequentially connected to... The system comprises a first and second quantitative ring, a matrix matching blank cylinder and a target gas depletion cylinder, an equalizing valve, a four-way reversing valve, a first and second photoacoustic cavity, and a drain and flushing manifold. A semiconductor laser is connected to the entrance windows of the two photoacoustic cavities via a beam splitter. First and second optical power monitors are positioned after their respective exit windows. First and second microphones are positioned at the acoustic pressure belly of their respective photoacoustic cavities. First and second miniature microphones are positioned on the cavity walls adjacent to their respective microphones. Pressure, temperature, volumetric flow rate, microphone, optical power, and valve position feedback terminals are connected to the input terminals of the controller. The output terminals of the controller are connected to the inlet valve, return valve, vacuum valve, gas collecting valve, degassing actuator, four-way reversing valve, laser, preamplifier, and phase-locked demodulator.

[0020] Preferably, the controller includes a degassing state machine and a detection state machine; the degassing state machine drives the valve group in the sequence of the k-th vacuum-induced degassing action, the k-th constant-volume isolation window measurement, the k-th incremental gas transfer, and the (k+1)-th vacuum-induced degassing action, and only when... and Gas mixing is permitted only after the closure verification is passed; the detection state machine drives the valve group in a non-skipped sequence of evacuation and leak detection, equal-volume filling of the same batch, consumption / blank pairing, dark light and sound-electric self-test, A valve position measurement, B valve position measurement, evacuation and flushing, and zero-point retest, and only when... When the acoustic-electric channel drift, resonance tracking, laser power, and zero-point retest are all qualified, the output will be... .

[0021] Compared to existing technologies, this invention discloses a high-precision and rapid detection method based on a vacuum degassing device and a photoacoustic cell. ①After the action The maximum value type endpoint index controls the vacuum degassing action, and with Verifying the gas collection closure can simultaneously reduce system deviations caused by under-gas removal and gas path leakage; ②Ultrasonic energy is limited by cavitation broadband index and oil cracking risk threshold, and ultrasound is only used as an optional nucleation action; it can be skipped when its benefits do not meet the threshold, and it will no longer be forced to participate in each cycle in order to collect keywords; ③ By using isochoric sampling of the same batch of homogenized gas, pairing of consumption cylinders / blank cylinders, and hard criteria of pressure-temperature-flow rate, the reference retains the background of oil vapor, water vapor, and non-target gases in this cycle, while also providing the residual acetylene ratio. ; ④ By swapping the roles of sample gas S and reference gas R between two equally illuminated photoacoustic cavities, and then calculating the difference between the two channel values, fixed channel gain, window background, and in-phase mechanical noise can be eliminated; the dim light emission self-test further prevents faulty channels from participating in concentration output; ⑤ Through A mass balance with a unified dimension is constructed with the final residual dissolved amount, and the free gas result of the gas relay is first converted into the equivalent concentration in the oil before comparison, so as to avoid directly dividing the gas phase mole fraction with the concentration in the oil. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the system structure connection of the present invention; Figure 2 This is a schematic diagram of the composite vacuum degassing module structure of the present invention; Figure 3 This is a schematic diagram of the paired gas paths, role interchange, and dual-differential structure of the same batch of inventions; Figure 4 This is a schematic diagram of the method flow of the present invention; Figure 5 This is a schematic diagram illustrating the dimensionless verification of the rapid detection of free gases and the integrity detection of oil samples in this invention. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] like Figure 1As shown, the system includes, in sequence along the oil sample direction, a transformer oil tank 100, a quantitative oil sampling and return unit, and a composite vacuum degassing module 200; and in sequence along the gas direction, a gas collection and homogenization chamber 220, a batch-paired gas path module 230, a dual-channel resonant photoacoustic module 300, and a drain and flushing manifold 237. The lower oil inlet and return port of the composite vacuum degassing module 200 are connected to the oil tank via an oil inlet valve 219 and a return valve 221, respectively. The top vacuum port is connected to a vacuum source via a vacuum valve 222, and the top gas collection port is connected to the gas collection and homogenization chamber 220 via a gas collection valve 223. The safety gas collection interface of the gas relay 110 only provides free gas samples to the batch-paired gas path and does not change the original protection trip circuit.

[0025] In the dual-channel resonant photoacoustic module 300, the laser 310 is connected to the entrance windows of the first photoacoustic cavity 321 and the second photoacoustic cavity 322 via a beam splitter 311; the first and second optical power monitors 340 are located after their respective exit windows; the first microphone 324 and the second microphone 325 are located at their respective sound pressure levels; and the first and second miniature microphones 326 and 327 are located near the cavity walls of their respective microphones. Pressure, temperature, flow rate, optical power, microphone, and valve position feedback are fed into the controller 400. The controller output is connected to each pump valve, degassing actuator, laser, and phase-locked demodulator 330, thereby giving the medium path, optical path, and signal path definite start and end points.

[0026] Confined cavitation combined vacuum degassing: such as Figure 2 As shown, the composite vacuum degassing module 200 employs a sealed degassing chamber 210 to support multiple degassing mechanisms. A quantitative oil sample enters through the lower inlet and flows back through the lower return outlet, retaining a known effective volume above the oil surface. The top of the chamber is covered by a headspace; a spray head 213 is located at the center of the top cover; a piston 211 slides from the bottom seal; a stirrer 214 is immersed in the oil sample; and an ultrasonic transducer 212 and a low-frequency vibrator 218 are coupled to the lower cavity wall. A pressure sensor 215 is located on the headspace sidewall; an acoustic emission sensor 216 is located on the cavity wall near the gas-liquid interface; and a temperature sensor 217 is immersed in the oil sample. All three are connected to the controller 400.

[0027] The control timing is as follows: when the k-th vacuum degassing action is executed, only the corresponding actuator is enabled; after the action is completed, the oil inlet valve 219, oil return valve 221, vacuum valve 222, and gas collecting valve 223 are closed to form the k-th constant volume isolation window and the start and stop status is collected; calculation Afterwards, only the gas collecting valve 223 is opened to transfer the incremental gas to the gas collecting and homogenizing chamber 220; the gas collecting valve is closed only after the pressure difference reaches the transfer completion threshold, allowing the (k+1)th vacuum degassing action to proceed. The last qualified window... Enter the calculation of residual dissolved amount.

[0028] Let the volume of the oil sample be... The absolute pressure of the top headspace of the last qualified isolation window is The mole fraction of the target gas in the homogenized gas is The total number of moles of all the gases removed is .by Indicates oil temperature If the solubility coefficient of the target gas is given, then the target gas contained in the initial oil sample is equal to the sum of the target gas in the transferred gas phase and the target gas remaining in the final state in the oil: (1) In equation (1), The unit is mol / m 3 , The unit is m 3 , The unit is mol. It is a dimensionless mole fraction. The unit is , The unit is . From equation (6), we get Equation (14) is obtained, and Equation (1) is rearranged to form Equation (15) for on-site calculation.

[0029] Ultrasound is not necessarily better the higher the power. This invention utilizes an acoustic emission sensor 216 to simultaneously calculate the ratio of cavitation high-frequency broadband energy to the transducer's fundamental frequency / lower harmonic energy: (2) In equation (2), A(f) is the amplitude of the acoustic emission spectrum; Covering the fundamental frequency and low harmonics from 20 to 80 kHz, It covers a cavitation bandwidth of 100–500 kHz. The controller is calibrated using a blank oil sample. and stability threshold achieve Stop ultrasonic testing if the oil temperature rises by more than 2°C or the acetylene increment in the blank oil exceeds the limit.

[0030] After each vacuum degassing operation, the inlet valve, return valve, and gas collecting valve are closed, and the effective headspace volume is determined. The start and end pressures, temperatures, and compressibility factors are recorded within the unchanging isolation window. The number of new gas moles released into the top headspace during the k-th action is: (3) In equation (3), These represent the start and end states of the k-th isolation window, respectively; R is... After the window ends, the incremental gas is transferred to a pre-evacuated gas collection and homogenization chamber before the next operation begins. It has a clear physical affiliation.

[0031] Define the marginal gas release per unit time for the k-th action. And define the unit comprehensive cost and predict the revenue for candidate action a. : (4) In equation (4), The duration of the action already performed. These represent the predicted gas release, prediction time, and energy consumption for candidate action a under the current oil temperature, pressure, and viscosity conditions. These are the weights determined during the equipment calibration phase. It is only used to select the next action; it does not enter the final concentration formula.

[0032] To prevent a low-value indicator from compensating for another unstable indicator, the degassing completion indicator is taken as the maximum value among the three normalized values: (5) In equation (5), The marginal gas release volume for the first effective action. For the allowable pressure recovery rate, The allowable residual cavitation intensity after ultrasounding has ceased. Only when... Degassing can only be terminated when two consecutive actions are no greater than 1, and the oil temperature, liquid level, and pressure are all within the safety window.

[0033] After degassing, all the gas released from each isolation window was transferred to a pre-evacuated container with a volume of [missing information]. The gas collection and homogenization chamber is allowed to stand until the pressure is reached. and temperature Stable, and calculate the total number of moles of gas collected and the closure error of the amount of substance: (6) In equation (6), It is the compressibility factor of the mixed gas in the gas collection and homogenization chamber. When the value is not greater than the calibration upper limit (preferably 2%), the generated value includes... The degassing and gas collection certificate is executed according to the action sequence; otherwise, a leak check and regassing are performed without outputting the concentration.

[0034] The same-batch paired gas path and role-reversal dual differential: The same-batch paired gas path module 230 is set between the gas collection and homogenization chamber 220 and the first photoacoustic chamber 321 and the second photoacoustic chamber 322. The outlet of the gas collection and homogenization chamber is divided into two equal-length branches via an inlet valve, which are respectively connected to the first metering loop 231 and the second metering loop 232 with a volume difference of no more than 1%; the first branch is then connected to the matrix matching blank cylinder 234 to form the sample gas S, and the second branch is connected to the target gas depletion cylinder 233 to form the reference gas R. The outlets of the two cylinders are connected to the two inlets of the four-way reversing valve 235 via the pressure equalization valve 236. The two outlets of the four-way reversing valve are respectively connected to the inlets of the two photoacoustic chambers, and the outlets of the two photoacoustic chambers are connected to the drain and flushing manifold 237. The pressure, temperature and volumetric flow rate sensor group 410 is located on the two branches upstream of the four-way reversing valve and is used to form the pairing error. .

[0035] The valve assembly operates according to S0 through S5 without skipping any steps: S0 closes the oil inlet valve and evacuates the gas collection and homogenization chamber, the two metering rings, and the two photoacoustic chambers, performing leak detection based on the pressure holding value; S1 simultaneously fills the two metering rings with the qualified gas collection and homogenization gas; S2 allows the two branches to pass through the blank cylinder and the loss cylinder respectively, and then through the pressure equalization valve to achieve isobaric and constant temperature operation, outputting... S3, with valve A in position A, allows S to enter the first photoacoustic cavity and R to enter the second photoacoustic cavity; S4, with valve B in position B, allows R to enter the first photoacoustic cavity and S to enter the second photoacoustic cavity; S5, venting through the common manifold, flushing with target consumption reduced gas, and re-measuring the zero point. The output of each state serves as the release condition for the next state.

[0036] Residual ratio of consumption Calibration was performed using standard mixtures with varying acetylene concentrations, oil vapor content, and water content; pairing error. It is formed by the pressure, temperature, and volumetric flow rate of the two upstream branches of the four-way directional valve. If The results of this cycle are invalidated and the same batch of gas is taken again in S1. The incidental effects of the adsorbent material on water vapor, oil vapor or flow resistance are not taken as the acetylene difference.

[0037] Table 1. Paired Gas Circuit Valve Status Control Table for the Same Batch

[0038] Define the target gas consumption residual ratio Pairing error between sample gas and reference gas : (7) In equation (7), denoted as the mole fraction of the target gas in sample gas S and reference gas R, respectively; P, T, and F are the inlet pressure, temperature, and volumetric flow rate, respectively. It can serve as an initial window, which is ultimately determined by paired standard gas tests. Enter formula (14). It is used only as a hard validity criterion.

[0039] Resonant Frequency Prediction and Online Tracking: The first photoacoustic cavity 321 and the second photoacoustic cavity 322 of the dual-channel resonant photoacoustic module 300 use the same materials, dimensions, windows, and microphone mounting methods. Gas inlets are located at one end of each cavity, with the entrance window on the same side as the gas inlet and the exit window at the opposite end. The first and second optical power monitors 340 are located after their respective exit windows. The first microphone 324 and the second microphone 325 are fixed at the first-order longitudinal sound pressure level of the two cavities, and the first and second miniature microphones 326 and 327 are located on the sidewalls adjacent to the corresponding microphones. Because cavity temperature, gas composition, and thermal expansion change the actual resonant frequency, the controller first predicts the sweep frequency window using the following formula: (8) In equation (8), Reference temperature Equivalent molar mass of reference gas and specific heat ratio The calibrated resonant frequency is below; Estimated based on the temperature, pressure, and matrix composition of the two photoacoustic cavities from the same batch; is the coefficient of linear expansion of the cavity material. It only limits the frequency sweep window and does not directly serve as the final resonant frequency.

[0040] exist After coarse and fine scanning of the neighborhood, the laser sinusoidal modulation frequency is updated using the difference between the phase of the second harmonic complex signal and the target phase. (9) In equation (9), Let k be the sinusoidal modulation frequency updated. This is the second harmonic phase error. For proportional and integral coefficients; the control objective is If the peak amplitude deviates from the zero-crossing frequency of the phase by more than 0.5%, first check the pairing certificate and channel self-test, and then rescan the frequency.

[0041] Photoacoustic concentration and oil concentration inversion: using the target gas depletion residual ratio β i Target spectral line calibration coefficients The average value of the readings of the first and second optical power monitors at the A / B valve position. And the quality factor Q obtained from the frequency sweep in this cycle, for the double difference component of role swap. Inversion was performed to obtain the mole fraction of the target gas in the homogenized gas. : (14) In equation (14), Using acetylene standard gas at different chamber temperatures and cavity pressure The subscript includes the absorption line intensity, cell constant, and acoustic-electric sensitivity normalized by equation (12); The average power of the two valve positions (A and B) and the two optical paths is taken; Q is obtained from the half-power bandwidth of the current cycle sweep. Output Direct entry (15).

[0042] The result obtained from equation (14) With the output of the degassing section Quantitative sampling Oil temperature corresponding And the last qualified volume-controlled isolation window Substituting all values ​​into equation (15), the target gas concentration in the oil is obtained; if any pre-stage output is missing, equation (15) will not be executed: (15) The first parenthesized term in equation (15) This indicates the contribution of the target gas, which has been transferred to the gas homogenization chamber, to the oil sample concentration. (Second item) This indicates the contribution of the target gas that is still dissolved in the oil at the end of the degassing process. In mol / m 3 The output is then converted to mg / kg or ppm based on the target gas molar mass and the measured oil density for this cycle; no empirical efficiency or additional rate terms are introduced.

[0043] To avoid directly adding errors of different dimensions, let ,but The relative standard uncertainty is written as: (16) In equation (16), Depend on The uncertainty propagation is obtained; Depend on The transmission is successful. If any pairing, self-test, gas collection closure, or uncertainty certificate exceeds the limit, the system will not output a high-precision flag.

[0044] Gas relay event-triggered closed loop: Gas relay 110 retains its original light gas, heavy gas, and oil flow protection functions; the detection system only obtains free gas from the safety gas collection interface, without changing the protection trip circuit. Free gas first... Figure 5 The upper branch completes batch pairing, acoustic-electrical self-test, and A / B role swapping. The resulting gas phase mole fraction is converted based on sampling volume, temperature, and pressure. ;Then the oil sample along Figure 5The lower branch is fully generated Only after converting the two to the same concentration dimension in the oil can a consistent index be formed.

[0045] Define a consistency index between free gas and dissolved gas in oil: (17) In equation (17), To convert the mole fraction of free gas into the equivalent concentration in oil under the same temperature, pressure, and dissolution model, For the oil sample results of equation (15), The sampling time difference between the two sources This is the dissolution / migration time constant. Consistency indices are only calculated after conversion to the same dimensions. This indicator is for diagnostic assistance only and does not replace the gas relay protection logic. Laser modulation, acoustic self-test, and role-reversal demodulation: Laser 310 is preferably a DFB semiconductor laser in the 1510–1540 nm wavelength band. In this embodiment, the acetylene absorption line at approximately 1531.59 nm is selected; the laser temperature is controlled by a closed-loop thermoelectric cooler, and the current is controlled by a low-noise driver. A slow triangular wave is used to cross the absorption line to find the center, and a fast sine wave is used for wavelength modulation. The drive current is expressed as: (10) In equation (10), Driven by the center current, These represent the current amplitudes of the triangular wave and the sinusoidal wave, respectively. The scanning frequency is 0.05–0.5 Hz. satisfy The two photoacoustic cavities are irradiated by the same laser beam splitting, and the real-time optical power after beam splitting is recorded and normalized in equation (14).

[0046] The laser wavelength is affected by both the driving current and the junction temperature. Feedforward compensation is performed using a reference photodiode and a temperature sensor. (11) In equation (11), These are the current-wavelength coefficient and the temperature-wavelength coefficient, respectively. For laser temperature. The controller sets... The error, reference optical power error, and absorption line center error are respectively fed back to the thermoelectric cooler, modulation amplitude, and... .

[0047] A first miniature microphone 326 and a second miniature microphone 327 are respectively installed next to the first microphone 324 and the second microphone 325. When the laser is off, both chambers are filled with target gas and isolated by the four-way reversing valve 235 and the vent valve, the same standard electrical signal is input to the two microphones. The complex transfer coefficients of the two acoustic and electrical channels are obtained. and use The normalized signal corresponds to the subsequent photoacoustic complex signal of the microphone; the self-test of the microphone only covers the microphone-preamplifier-locked-middle-acoustic cavity link, and does not cover the laser wavelength and molecular absorption.

[0048] (12) In equation (12), j = 1, 2, The phase-locked complex signal is excited by the sound generator. The reference transfer factor is the one saved during the most recent standard gas maintenance. This represents the maximum relative drift of the channel. If the phase difference exceeds 5% or the phase difference between the two channels exceeds 5°, the current cycle is invalid and a maintenance alarm is output. The generator self-test does not cover the light source and molecular absorption stages.

[0049] Record the data at valve position A of the four-way directional valve 235. Normalized Record at valve B position Maintain the same modulation frequency between the two valve positions. The phase-locked integration time, cavity temperature, and cavity pressure are recorded, and the readings of the first and second optical power monitors 340 are recorded simultaneously. The four normalized complex signals are fed into equation (13) to obtain , It is not directly output as concentration, but rather combined with... Common entry (14). Role reversal double difference components are: (13) In equation (13), the superscripts A and B represent the two valve positions of the four-way directional valve. If the first photoacoustic cavity has a fixed background... The second photoacoustic cavity has a fixed background. ,but The signs in the two parentheses are the same and are eliminated by subtraction; the target gas signal changes sign as S and R are interchanged and is retained.

[0050] The following examples illustrate how measurement data propagates along the formula chain and do not limit the scope of protection. Regarding the quantitative release and role-reversal detection of acetylene in oil, [the following is taken]... Mineral insulating oil sample, effective headspace volume Constant temperature Effective volume of gas collection homogenization chamber The pressure sensor is evacuated before the start of each cycle. The pressure sensor has a range of 0–120 kPa (absolute pressure) and an accuracy of not less than 0.05%FS; the temperature sensor has an allowable error of ±0.05℃ after calibration.

[0051] Table 2 Comparison of Implementation Parameters and Applications

[0052] First, execute three 5-second ultrasound pulses; near Immediately reduce power or stop. Expand the piston to an absolute pressure of 12 kPa and superimpose a low-frequency vibration of 12 Hz for 15 s. After each action, calculate according to formula (3) within the constant-volume isolation window. The incremental gas is then transferred to the gas collection and homogenization chamber. The controller compares the spraying and stirring according to equation (4). When two consecutive actions Stop at this time. The stable value of the gas collection homogenization chamber in this example is calculated as follows: Therefore The closure threshold is achieved by using 2% of the gas collection volume.

[0053] During the gas mixing stage, two 1.0 mL metering loops simultaneously sampled from the gas collection and homogenization chamber. Standard gas calibration was then performed. The sample gas S and the reference gas R were both introduced into the chamber at pressures of 90.0±0.5 kPa and temperatures of 35.0±0.1℃, with a relative flow rate difference of 1.1%. Therefore... The self-test for dim light and sound output was obtained. Substituting the normalized complex signals of bits A and B into equation (13), and then using equation (14) to obtain... .like ,but: (18) The mass concentration conversion in formula (18) uses the molar mass of acetylene of 26.038 g / mol and the measured oil density of 860 kg / m³ in this period. 3 0.0330 mol / m 3 This corresponds to 0.859 mg / L, which is approximately 1.00 mg / kg. Both the residual dissolution term and the value of the residual dissolution term should be obtained by measurement or calibration of the prototype. This example only proves the closure of the formula before and after the formula and the units, and does not claim to be the actual measured performance of the prototype.

[0054] During the detection phase, frequency sweeping and frequency tracking are performed first using equations (8) and (9), then the laser is turned off and self-tested according to equation (12). After passing the self-test, the four-way reversing valve is held in position A and position B for 1 second each, and the two valve positions use the same modulation frequency, integration time, and optical power normalization. Equation (13) outputs Equation (14) output Equation (15) output The estimated time for the entire process is as follows: sampling and temperature control 30-60 s, vacuum degassing and gas collection 60-120 s, gas mixing / self-test / reversal 15-30 s, frequency sweep and demodulation 5-20 s, totaling approximately 110-230 s.

[0055] Free gas rapid detection triggered by gas relay: When the gas relay light gas contact activates or the accumulated gas reaches 50 mL, 2.0–5.0 mL of free gas is taken from the safety gas collection port and enters the gas collection and homogenization chamber. Two quantitative loops sample simultaneously, forming S and R respectively through the matrix matching blank cylinder and the target gas depletion cylinder, and then perform dark light self-test, A / B valve position role interchange and double differential detection of equations (13) and (14); the free gas mole fraction is obtained within 10–30 s. Subsequently, the oil sample detection of Example 1 is automatically performed, and the free gas result is converted into Substitute into equation (17).

[0056] Range and anti-saturation strategy: When the second harmonic amplitude of any channel obtained by the initial short scan exceeds 80% of the upper limit of the linear range, the two quantitative loops are diluted with calibrated target gas of the same source at the same volume ratio, and the dilution factor is written into the calibration coefficients of the sample gas and the reference gas. When the signal approaches the detection lower limit, the phase-locked integration time is gradually increased from 0.5 s to 3 s. After any range switch, the acoustic self-test of S1 to S5 and Equation (12) and the A / B valve position measurement must be re-executed. It is not allowed to simply adjust the electronic gain and then use the old pairing certificate.

[0057] Table 3 Recommended Testing Parameters and Acceptance Criteria

[0058] Calibration and verification methods: The final prototype must complete at least six types of calibration. First, calibration using blank insulating oil. And the blank acetylene increment. Second, calibration with standard oil samples. The degassing endpoint threshold and the final state residual dissolution model were established. Third, the consumption reduction cylinder was calibrated using a standard mixture of oil vapor and water vapor. Matrix retention rate of blank tubes and Threshold. Fourth, calibration using standard gases with different acetylene concentrations. And linear range. Fifth, save using standard transmitter signals. A self-test drift threshold is set, and it is clarified that this step does not calibrate optical absorption. Sixth, the A / B valve position dual differential is verified under ambient temperature and mechanical vibration disturbances. The closure and recovery rate of formula (15); the detection limit and repeatability are statistically analyzed based on at least 6 independent samples, and formula (18) is not used to replace the actual measurement.

[0059] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0060] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-precision and rapid detection method based on a vacuum degassing device and a photoacoustic cell, used to detect target gases dissolved in insulating oil, characterized in that, include: With volume A quantitative oil sample is fed into the sealed degassing chamber through the inlet at the bottom of the chamber and kept at a constant temperature, forming an effective volume of [missing information] above the oil sample. Top headspace; Each vacuum degassing action is numbered k according to its execution time, where k is a positive integer. After the kth vacuum degassing action is completed, the inlet valve, return valve, vacuum valve, and gas collecting valve are closed to form the kth constant-volume isolation window. The absolute pressure of the top headspace is collected at the start and end times of this window. Thermodynamic temperature and compressibility factor Calculate the number of newly released moles corresponding to the k-th vacuum-assisted degassing action. and marginal gas release per unit time and will Benefits of candidate actions Used to select the (k+1)th vacuum-assisted degassing action until the degassing is completed. The endpoint condition is continuously satisfied; After each measurement at the constant volume isolation window is completed, the corresponding incremental gas is transferred through the gas collection port at the top of the sealed degassing chamber to a pre-evacuated chamber with an effective volume of [missing information]. After the gas collection and homogenization chamber is completed, the gas collection valve is closed before the next vacuum degassing action is allowed; After the degassing endpoint, the pressure in the gas collection and homogenization chamber is used as a guide. ,temperature Compression factor The total number of moles of gas collected was obtained. and will and relative deviation As a criterion for gas collection closure, only when If the sample passes the test, the homogenized gas is allowed to proceed to subsequent tests. Simultaneously, the first and second metering loops are filled with homogenized gas from the same batch that has passed through a closed loop. The gas in the first metering loop passes through a matrix-matched blank cylinder to form a sample gas S containing the target gas. The gas in the second metering loop passes through a target gas depletion cylinder to form a target gas residual ratio of [missing value]. The reference gas R is used, and a pairing error is formed based on the pressure, temperature, and volumetric flow rate of S and R before they enter the cavity. ; In valve position A of the four-way reversing valve, S enters the first photoacoustic cavity and R enters the second photoacoustic cavity; in valve position B, R enters the first photoacoustic cavity and S enters the second photoacoustic cavity. The first photoacoustic cavity and the second photoacoustic cavity are both illuminated by the same semiconductor laser beam splitting. The first microphone and the second microphone are respectively located at the sound pressure level of the first photoacoustic cavity and the second photoacoustic cavity. The first micro-sound generator and the second micro-sound generator are respectively located on the cavity wall adjacent to the corresponding microphone. The first optical power monitor and the second optical power monitor are respectively located after the exit window of the two photoacoustic cavities. The complex transfer coefficients of the first and second acoustic-electric channels were obtained using two miniature sound generators. The second harmonic complex signals of valve positions A and B are obtained using two microphones. , and by Normalization Where j = 1, 2; The difference between the channel values ​​of the two valve positions is subtracted again to obtain the role-swap double difference component D. i ,according to Target spectral line calibration coefficients Average laser power of two channels The quality factor Q obtained from the frequency sweep in this period is used to invert the mole fraction of the target gas in the homogenized gas. ; Will Oil temperature The target gas solubility coefficient and the final state pressure of the last qualified constant volume isolation window. Substituting into the mass balance, the concentration of the target gas in the oil sample is obtained. And only in When the self-test of the acoustic and electrical channels, resonance tracking, and zero-point retest all pass, output... And a test certificate containing all the preceding parameters and results.

2. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: The volume of the oil sample The effective headspace volume is 80–150 mL. The sample volume is 15–40 mL, and the oil sample temperature is [not specified]. The temperature is 40–55°C, and the absolute pressure during the kth vacuum degassing action is 5–25 kPa; the effective volume of the sealed degassing chamber in the kth constant-volume isolation window remains unchanged, and the start and end states of this window are correlated with the type and duration of the kth vacuum degassing action. and motion energy consumption Binding storage.

3. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: The vacuum-assisted degassing action includes at least one of piston expansion, vacuum spraying, stirring, and low-frequency vibration, and an ultrasonic pulse of 20–40 kHz, 10–80 W, and 5–45 s can be executed before the action; the cavitation intensity is defined as the ratio of cavitation broadband energy of 100–500 kHz to the energy of the fundamental frequency and low-order harmonics of 20–80 kHz. Only the nucleation threshold calibrated on blank oil samples With the risk threshold of pyrolysis The ultrasonic pulses are allowed between them.

4. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: The number of newly released moles in the k-th vacuum-assisted degassing action according to Calculate the marginal gas release per unit time. ; Action benefit of candidate action a The controller selects the candidate action from those that meet the requirements of pressure, level, temperature, and cavitation safety window by using the weighted sum of the predicted new gas release amount, predicted action time, and predicted action energy consumption. The largest action is the (k+1)th vacuum-assisted degassing action.

5. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: Degassing completion target Pick The ratio of pressure recovery rate to its threshold and The maximum value among the ratios to the stability threshold; Degassing was stopped after at least two consecutive tests with a value not exceeding 1; total number of moles of gas collected. Relative deviation of gas collection closure , If the gas volume is not greater than the preset upper limit, a degassing-gathering certificate is generated and gas mixing within the same batch is allowed; otherwise, a leak check is performed, gas is re-gathered, and the original gas is not reused. .

6. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: The paired gas path modules of the same batch are set between the gas collection and equalization chamber and the first and second photoacoustic chambers. Along the airflow direction, they include an inlet valve, a first metering ring and a second metering ring, a matrix matching blank cylinder and a target gas depletion cylinder arranged in parallel, a pressure equalization valve, a four-way reversing valve, and an exhaust flushing manifold connected to the outlet of the two photoacoustic chambers. The matrix matching blank cylinder and the target gas depletion cylinder have the same carrier, geometric dimensions, filling amount and flow resistance. The target gas depletion cylinder retains the target gas selective active sites, and the corresponding active sites of the matrix matching blank cylinder are passivated.

7. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 6, characterized in that: Target gas residual ratio β i The value calibrated by standard gas is no greater than 0.

05. Pairing error between sample gas S and reference gas R ,in The data are collected by pressure, temperature, and volumetric flow rate sensors installed in the two upstream branches of the four-way directional valve, respectively. If the value is greater than 1, the role swap double difference will not be performed and the gas will be re-matched.

8. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: With the laser optical path closed, and both the first and second photoacoustic cavities filled with target dissipation gas and isolated from the paired gas path, the same standard electrical signal is input to the first and second miniature sound generators to obtain the complex transfer coefficients of the first and second acoustic-electric channels at their actual resonant frequencies. and with The subsequent photoacoustic complex signal is normalized; the self-test is only used to determine whether the transmission link of the first microphone, the second microphone, the dual-channel preamplifier, the phase-locked demodulator and the acoustic cavity has drifted, and does not replace the calibration of the target gas standard gas concentration.

9. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: The resonant frequency is predicted based on the cavity temperature, equivalent molar mass of the gas, specific heat ratio, and thermal expansion of the cavity in the first and second photoacoustic cavities. ,exist The system performs coarse and fine frequency sweeps, updating the modulation frequency based on the phase error of the second harmonic complex signal obtained from the first and second microphones. The quality factor Q is calculated from the half-power bandwidth of the frequency sweep in this cycle; They will then proceed to subsequent phase-locked demodulation and... Inversion.

10. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: The semiconductor laser is a distributed feedback semiconductor laser in the 1510–1540 nm wavelength band, with a laser temperature control error of no more than ±0.01℃ and a drive current ripple of no more than 0.01% of full scale; the target absorption line is scanned with a triangular wave at a frequency of f. r A sine wave of 2 / 2 is used for wavelength modulation, and second harmonic phase-locked demodulation is performed with an integration time of 0.5–3 s. The average laser power of the two paths is formed by the readings of the first and second optical power monitors. .

11. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: Role swap double difference components Mole fraction of target gas in homogenized gas Target gas concentration in oil sample ;in The output only enters Inversion, The output is only related to They collectively enter into oil quality equilibrium.

12. The high-precision rapid detection method based on a vacuum degassing device and a photoacoustic cell according to claim 1, characterized in that: When the gas relay's light gas contact activates, the accumulated free gas volume reaches a threshold, or the gas production rate reaches a threshold, the free gas is sent to the paired gas circuit module of the same batch for rapid detection via the safety gas collection interface and the oil mist removal branch without altering the protection trip circuit. Then, the oil sample vacuum degassing detection is initiated. The free gas detection results are converted into equivalent concentrations in the oil based on the sampling volume, temperature, and pressure. Then, with The consistency index is formed by the time difference between the two samplings.

13. A high-precision, rapid detection system for implementing the method according to any one of claims 1 to 12, characterized in that: The system includes a quantitative oil sampling and return unit, a composite vacuum degassing module, a vacuum source, a gas collection and homogenization chamber, a batch-matching gas path module, a dual-channel resonant photoacoustic module, and a controller. The quantitative oil sampling and return unit is connected to the lower oil inlet of the composite vacuum degassing module via an oil inlet valve and to its lower oil return port via a return valve. The top vacuum port of the composite vacuum degassing module is connected to the vacuum source via a vacuum valve, and the top gas collection port is connected to the gas collection and homogenization chamber via a gas collection valve. A pressure sensor is installed on the top headspace sidewall, a temperature sensor is immersed in the oil sample, and an acoustic emission sensor is installed near the gas-liquid interface on the chamber wall. The outlet of the gas collection and homogenization chamber is sequentially connected to the first and second quantitative rings, a matrix matching blank cylinder and a target gas consumption cylinder, a pressure equalization valve, a four-way reversing valve, the first and second photoacoustic chambers, and an exhaust flushing manifold. The semiconductor laser is connected to the entrance windows of the two photoacoustic cavities via a beam splitter. The first and second optical power monitors are respectively set after the corresponding exit windows. The first and second microphones are respectively set at the sound pressure level of the corresponding photoacoustic cavity. The first and second miniature microphones are respectively set on the cavity wall adjacent to the corresponding microphones. The pressure, temperature, volumetric flow rate, microphone, optical power and valve position feedback terminals are connected to the input terminal of the controller. The output terminal of the controller is respectively connected to the oil inlet valve, oil return valve, vacuum valve, gas collection valve, degassing actuator, four-way reversing valve, laser, preamplifier and phase-locked demodulator.

14. The high-precision rapid detection system based on a vacuum degassing device and a photoacoustic cell according to claim 13, characterized in that: The controller includes a degassing state machine and a detection state machine; the degassing state machine drives the valve group in the sequence of the k-th vacuum-induced degassing action, the k-th constant-volume isolation window measurement, the k-th incremental gas transfer, and the (k+1)-th vacuum-induced degassing action, and only when... and Gas mixing is permitted only after the closure verification is passed; the detection state machine drives the valve group in a non-skipped sequence of evacuation and leak detection, equal-volume filling of the same batch, consumption / blank pairing, dark light and sound-electric self-test, A valve position measurement, B valve position measurement, evacuation and flushing, and zero-point retest, and only when... When the acoustic-electric channel drift, resonance tracking, laser power, and zero-point retest are all qualified, the output will be... .

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