Sulfur hexafluoride on-line mixing ratio density detection and dual-verification sensor

Abstract

The invention relates to a sulfur hexafluoride online mixing ratio density detection and dual-check sensor, and belongs to the technical field of gas detection. According to the sensor, the mixing ratio and density of SF6 gas are detected by utilizing the physical characteristics of the piezoelectric effect of the quartz crystal. The sensor comprises a QCM detection unit, a dual-verification unit, a data processing unit, a communication unit and a power supply unit, the QCM detection unit is constructed by utilizing the physical characteristics of the piezoelectric effect of a quartz crystal, and the QCM detection unit comprises a quartz crystal resonator, an electrode, a gas detection chamber and a frequency counter. According to the invention, real-time and accurate detection of the mixing ratio and density of SF6 gas and air or other gases can be realized; moreover, through a unique dual-verification mechanism, detection errors caused by various factors in a long-term operation process of the sensor are effectively eliminated, high reliability of a detection result is ensured, and a solid technical support is provided for safe and stable operation of power equipment and precise control of an industrial production process.

Description

Technical Field

[0001] The invention belongs to the technical field of gas detection, and in particular relates to a sulfur hexafluoride online mixing ratio density detection and double calibration sensor. Background Art

[0002] SF6 (sulfur hexafluoride) gas is widely used in high-voltage equipment in power systems due to its excellent insulation and arc-extinguishing properties. However, SF6 gas leaks can not only cause equipment failures, but also pollute the environment and pose safety risks. Therefore, real-time and accurate monitoring of the SF6 gas mixture ratio and density is crucial to ensuring the safe operation of power equipment.

[0003] While existing SF6 detection technology can achieve concentration detection to a certain extent, it still has shortcomings in the accuracy of mixing ratio and density detection, as well as long-term stability. In addition, existing technologies lack effective verification mechanisms, making it difficult to ensure the accuracy of sensors in long-term operation.

[0004] A quartz crystal microbalance (QCM) is a highly sensitive sensor based on the piezoelectric effect of quartz crystals, converting mass changes on an electrode surface into frequency changes. QCM technology offers advantages in gas detection, including high sensitivity, fast response, and the absence of markers. However, there are currently no reports on the application of QCM technology to SF6 mixture density detection, incorporating a dual-calibration mechanism. Summary of the Invention

[0005] The purpose of the present invention is to provide an online sulfur hexafluoride mixing ratio density detection and dual-calibration sensor, which can realize real-time and accurate detection of the mixing ratio and density of SF6 gas with air or other gases; and, through a unique dual-calibration mechanism, effectively eliminates detection errors caused by various factors during the long-term operation of the sensor, ensures the high reliability of the detection results, and provides solid technical support for the safe and stable operation of power equipment and the precise control of industrial production processes.

[0006] To achieve the above objectives, the technical solution of the present invention is: an online sulfur hexafluoride mixing ratio density detection and dual calibration sensor, which uses the physical properties of the piezoelectric effect of quartz crystal to detect the mixing ratio and density of SF6 gas.

[0007] Furthermore, the sensor includes a QCM detection unit constructed using the physical properties of the piezoelectric effect of a quartz crystal.

[0008] Furthermore, the QCM detection unit includes a quartz crystal resonator, an electrode, a gas detection chamber and a frequency counter; the quartz crystal resonator is the core component, and the electrode surface is coated with a functional material with high selectivity and high sensitivity to SF6 gas. When the gas containing SF6 enters the gas detection chamber and comes into contact with the electrode surface, the SF6 molecules will be adsorbed on the electrode surface, causing the mass of the electrode surface to change, causing the frequency of the quartz crystal resonator to change, and the frequency change of the quartz crystal resonator is measured by the frequency counter.

[0009] Furthermore, the calculation of the mixing ratio and density of SF6 gas is based on a pre-established mathematical model between the frequency change of the quartz crystal resonator and the SF6 gas concentration, mixing ratio and density.

[0010] Furthermore, a nanofiber membrane is deposited on the electrode surface, such as an electrospun polyacrylic acid PAA / polyvinyl alcohol PVA composite nanofiber membrane.

[0011] Furthermore, the sensor also includes a dual verification unit for ensuring the accuracy and reliability of the detection results.

[0012] Furthermore, the dual calibration unit includes an internal calibration module and an external calibration module; the internal calibration module is provided with a standard gas channel connected to a container storing standard SF6 gas of known concentration and density, and the standard gas channel is opened at a preset time interval to pass the standard SF6 gas into the gas detection chamber of the QCM detection unit, the QCM detection unit detects the standard SF6 gas and outputs corresponding measurement results, compares and analyzes the measurement results with the standard values, and calculates the error value of the sensor through the built-in calibration algorithm to perform real-time compensation for subsequent detection data; the external calibration module: an interface is provided for connection to an external standard gas source, and when high-precision calibration is required, the gas detection chamber of the QCM detection unit is connected to the external standard gas source, the external standard gas source has a second standard SF6 gas with higher accuracy and traceability than the standard SF6 gas, the QCM detection unit detects the second standard SF6 gas and outputs corresponding measurement results, and compares and analyzes the measurement results with the standard values to perform fine calibration of the sensor.

[0013] Furthermore, the sensor also includes a data processing unit; the data processing unit includes a microprocessor for processing and analyzing data collected by the QCM detection unit and the dual verification unit and a storage module for storing the data collected by the QCM detection unit and the dual verification unit.

[0014] Furthermore, the sensor also includes a communication unit for enabling communication between the sensor and the remote monitoring system and a power supply unit for supplying power to the entire sensor.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. High sensitivity detection

[0017] This invention utilizes QCM technology combined with nanofiber membrane-modified electrodes to achieve highly sensitive detection of SF6 gas mixture ratios and density. Compared to traditional detection technologies, it can detect lower SF6 gas concentrations, significantly improving the detection limit and accuracy. This enables the sensor to detect SF6 gas leaks in their early stages, providing stronger support for equipment maintenance and safety assurance.

[0018] 2. Double verification mechanism

[0019] The dual calibration mechanism of internal and external calibration ensures the sensor's accuracy over long-term operation from multiple perspectives. The internal calibration module compensates for sensor drift in real time, ensuring stability during daily operation. The external calibration module further verifies and improves sensor accuracy by comparing it with a high-precision standard gas source, effectively avoiding the accumulation of detection errors caused by long-term use or environmental changes, providing dual guarantees for the reliability of test results.

[0020] 3. Real-time monitoring and remote transmission

[0021] The sensor continuously monitors the SF6 gas mixture ratio and density in real time and transmits this data to a remote monitoring system via wireless communication. This allows operators to monitor and analyze sensor results in real time, anytime and anywhere, identifying potential safety hazards and equipment failures. Furthermore, the remote transmission function facilitates centralized management and data analysis of multiple sensors, improving monitoring efficiency and management capabilities.

[0022] 4. Frequency signal data algorithm

[0023] The sensor's sensing end utilizes specific dimensions and materials, resulting in an independently developed and designed product. This utilizes a proprietary algorithm to achieve a precise density response. The algorithm applies primary and secondary filtering to the raw impedance vs. frequency curve; the frequency value is then calculated against the corresponding density value, forming a unique product-specific calculation formula. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the overall block diagram of the sensor of the present invention.

[0025] Figure 2 FIG. 4 is a schematic diagram of a QCM detection unit circuit according to an embodiment of the present invention.

[0026] Figure 3 FIG. 4 is a schematic diagram of a dual-check unit circuit according to an embodiment of the present invention.

[0027] Figure 4 This is a schematic diagram of a microprocessor circuit according to an embodiment of the present invention.

[0028] Figure 5 FIG. 4 is a schematic circuit diagram of a storage module according to an embodiment of the present invention.

[0029] Figure 6 This is a circuit diagram of a communication unit according to an embodiment of the present invention.

[0030] Figure 7 This is a schematic diagram of a power supply unit circuit according to an embodiment of the present invention.

[0031] Figure 8 The following are curves of impedance and original value, primary filtering, and secondary filtering. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] The present invention provides a sensor for online sulfur hexafluoride mixing ratio and density detection and dual calibration. This sensor utilizes the physical properties of the piezoelectric effect of quartz crystals to detect the mixing ratio and density of SF6 gas. The sensor includes a QCM detection unit (using the piezoelectric effect of quartz crystals), a dual calibration unit, a data processing unit, a communication unit, and a power supply unit.

[0034] The following is a specific implementation process of the present invention.

[0035] The present invention provides a sulfur hexafluoride online mixing ratio density detection and dual calibration sensor mainly composed of the following parts:

[0036] 1.QCM detection unit

[0037] The QCM detection unit is the core detection component of the entire sensor. Its operating principle is based on the physical property of quartz crystal, the piezoelectric effect. When the quartz crystal is subjected to external physical quantities (such as mass changes), it produces a corresponding change in the electrical signal, specifically a change in frequency. In this invention, this property is used to detect the mixing ratio and density of SF6 gas.

[0038] The unit primarily consists of a quartz crystal resonator, electrodes, a gas detection chamber, and a frequency counter. The quartz crystal resonator serves as the core component, and its electrode surface is carefully coated with a functional material that exhibits high selectivity and sensitivity to SF6 gas. When SF6-containing gas enters the gas detection chamber and comes into contact with the electrode surface, SF6 molecules adsorb there, causing a slight change in mass. This mass change causes the frequency of the quartz crystal resonator to change, and the frequency counter accurately measures this frequency change in real time. Using a pre-established mathematical model linking this frequency change with SF6 gas concentration, mixing ratio, and density, relevant SF6 gas parameters can be accurately calculated.

[0039] The algorithm for the frequency and density of the QCM detection unit's detection values is as follows:

[0040] The change of density detection value is reflected by frequency value. The collected data includes impedance data and frequency data. Theoretically, the useful frequency value is the frequency value corresponding to the maximum impedance value. Each set of collected data (frequency value and impedance value) can form a curve graph, such as Figure 8 Impedance_Raw Value. Due to the influence of tiny particles and other trace impurities in the measured gas, the waveform generated by the raw data may contain glitches, affecting the determination of the frequency corresponding to the maximum impedance value. Therefore, the waveform is filtered twice: primary and secondary. The primary filter primarily eliminates glitches; the secondary filter stabilizes the impedance at its maximum value.

[0041] The algorithm formula of the first-level filtering is:

[0042] definition:

[0043] Selection of waveform glitch value: The change from the previous value is greater than the kn value (kn value is the fixed setting value of the system)

[0044] f——the current value of glitch frequency

[0045] f1——the first value before f

[0046] f2——the second value before f

[0047] f3——the third value before f

[0048] f'——Frequency value after first-level filtering

[0049] f=f'=(f1×3+f2×2+f3×1) / 6-Formula 1

[0050] The waveform is filtered using formula 1 and the graph example is shown in the figure. Figure 8 As shown in "Impedance_First-stage Filtering".

[0051] The algorithm formula of the secondary filtering is:

[0052] definition:

[0053] f'——Frequency value after first-level filtering

[0054] f”——Frequency value after secondary filtering

[0055] f'-1——the first value before f': (the second value before f' is f'-2, and so on)

[0056] f'1——the first value after f': (the second value after f' is f'2 and so on)

[0057] f”=[f'×6+(f'-1+f'1)×5+(f'-2+f'2)×4+(f'-3+f'3)×3+(f'-4+f'4)×2+(f'-5+f'5)×1] / 36-Formula 2

[0058] Figure 8 The three waveforms are:

[0059] Impedance_raw value (impedance and frequency values collected by the system);

[0060] Impedance_First-level filtering (Impedance_Original value calculated by formula 1, the waveform has been smoothed);

[0061] Impedance_Secondary Filtering (The frequency value after impedance_first-stage filtering is calculated using Formula 2, and the impedance peak value is more obvious).

[0062] In each set of data, the frequency value corresponding to the peak is extracted (f). Different gas density values correspond to frequency values one to one. The present invention uses specific dimensions and materials; after a large number of experimental studies, specific data is obtained and converted.

[0063] Conversion formula 3 (the present invention has formulated a formula according to the characteristics of its own product) is as follows:

[0064] definition:

[0065] f——frequency, unit: kHz

[0066] ρ——density, unit: kg / m 3

[0067] ρ=1374-113.4f+2.343f 2 -Formula 3

[0068] To further improve detection sensitivity, a nanofiber membrane, such as an electrospun polyacrylic acid (PAA) / polyvinyl alcohol (PVA) composite nanofiber membrane, is deposited on the electrode surface. This nanofiber membrane has a large specific surface area and rich pore structure, which can greatly increase the contact area and adsorption capacity of SF6 gas on the electrode surface, thereby significantly improving the sensor's response sensitivity and detection accuracy to SF6 gas.

[0069] like Figure 2 As shown in the figure, Quart INA and Quart INB in the QCM detection unit are the input terminals of the sensor, which provide excitation to the quartz crystal through the 6th pin of U17 and the operational amplifier of U16A, and then feedback to the internal ADC of the chip through the operational amplifier U16B to collect frequency information, and finally through the I 2 C interface to the MCU.

[0070] 2.Dual verification unit

[0071] The dual calibration unit is a key part of the present invention to ensure the accuracy and reliability of the detection results, and is composed of an internal calibration module and an external calibration module.

[0072] Internal Calibration Module: A dedicated standard gas channel is located within the sensor, connected to a container storing standard SF6 gas of known concentration and density. At preset intervals, the system automatically opens the standard gas channel, allowing standard SF6 gas to enter the gas detection chamber. The QCM detection unit then detects the standard gas and outputs the corresponding measurement results. These results are then compared with pre-stored standard values. A built-in calibration algorithm is then used to calculate the sensor's error. Subsequent test data is then compensated in real time, effectively compensating for sensor drift caused by prolonged use and environmental fluctuations, ensuring the sensor's accuracy over time.

[0073] External Calibration Module: To further verify and improve sensor accuracy, an interface for connecting to an external standard gas source is provided. When high-precision calibration is required, the operator can connect the sensor to an external, high-precision standard gas source. This external standard gas source provides standard SF6 gas with enhanced accuracy and traceability, which the sensor then tests and compares with the standard value. Based on this comparison, the sensor is finely calibrated to ensure that the sensor's test results are highly consistent with international or industry standards, thereby guaranteeing the sensor's accuracy and reliability over the long term.

[0074] like Figure 3As shown, the dual calibration unit has two calibration channels. The internal and external calibration are mainly composed of two operational amplifiers U1B, U1C and U1A, U1D and resistors and capacitors. The tiny signals generated by different gases are amplified by the operational amplifier and input to the instrument operational amplifier U2, and then compared with the reference voltage and amplified before output.

[0075] 3. Data processing unit

[0076] The data processing unit is responsible for processing and analyzing the data collected by the QCM detection unit and the verification unit. It mainly consists of a microprocessor and a storage module.

[0077] The microprocessor, as the core of data processing, possesses powerful computing and logic capabilities. It first collects and preprocesses the frequency change data output by the QCM detection unit to remove noise and outliers. It then performs further calculations and analysis based on pre-stored calibration parameters and mathematical models to accurately determine the SF6 gas mixing ratio and density. Simultaneously, the microprocessor processes the calibration data from the dual-calibration unit and adjusts detection parameters in real time based on the calibration results to ensure accurate test results.

[0078] The storage module stores important information such as test data, calibration parameters, and historical records. It can utilize high-capacity flash memory chips or other storage media to ensure secure data storage and long-term preservation. When needed, operators can remotely access the data in the storage module through the communication unit for data analysis and historical tracing.

[0079] like Figure 4 As shown, the microprocessor adopts a high-performance, low-power microcontroller, integrated with a single-precision floating-point unit (FPU) and DSP instruction set, supports real-time complex operations, and is equipped with 12-bit ADC / DAC, USB / CAN / SPI / I 2 C and other rich peripherals, it is very suitable for scenarios such as industrial control, portable devices and Internet of Things terminals that require a balance between power consumption and performance.

[0080] like Figure 5 As shown, the storage module uses serial Flash memory with an SPI-compatible interface and supports a wide voltage range of 2.3V-3.6V. Its internal structure consists of 4096 pages, each with 512 / 528 bytes, and is equipped with dual SRAM caches to enable high-speed continuous data stream writes. It is suitable for low-power, high-reliability embedded scenarios.

[0081] 4. Communication unit

[0082] The communication unit's main function is to transmit the sensor's detection results to the remote monitoring system in a timely and accurate manner, enabling remote monitoring and data analysis. It uses a wireless communication module, such as a Wi-Fi or 4G module.

[0083] The Wi-Fi module is suitable for scenarios where the sensor and monitoring system are close together and have stable Wi-Fi coverage. Through Wi-Fi, the sensor can quickly and reliably send detection data to a monitoring server or terminal device within the local area network, allowing operators to view and analyze data in real time.

[0084] The 4G module is suitable for use when sensors are installed in remote areas or without Wi-Fi access. It utilizes the mobile operator's 4G network to transmit detection data to a cloud server, enabling remote wireless transmission. Operators can access the cloud server anytime, anywhere via the internet to obtain real-time sensor detection data and historical records for remote monitoring and management.

[0085] like Figure 6 As shown in the figure, the communication unit uses a low-power 4G LTE Cat.1 wireless communication module designed based on the Unisoc UIS8910DM platform. It supports FDD-LTE / TDD-LTE long-distance communication, Bluetooth near-field transmission, and WiFi positioning. It also has expansion interfaces such as USB, UART, SPI, and I2C, making it suitable for remote communication, voice interaction, and intelligent control scenarios of IoT devices.

[0086] 5. Power supply unit

[0087] The power supply unit provides stable and reliable power to the entire sensor, ensuring it can function properly in various environmental conditions. It is battery-powered and equipped with a charging port.

[0088] The power source is a high-energy-density lithium battery, boasting large capacity, long life, and low self-discharge. This battery provides the sensor with a continuous and stable power supply, ensuring long-term, continuous operation. A charging port is also included to ensure timely recharging when the battery is low. This port can be connected to an external power adapter or solar panel, offering flexible charging options. Furthermore, the power supply unit utilizes an advanced power management chip to precisely control and manage the battery's charging and discharging processes, improving battery efficiency and lifespan, ensuring the sensor can operate for extended periods even without an external power source.

[0089] like Figure 7 As shown, the power input part F2, TVS2, ZD2, R48, and R42 in the power supply unit constitute overcurrent and overvoltage protection. The charging voltage can be set by R47, R55, and R52, and the charging current can be set by RSR1.

[0090] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A sulfur hexafluoride online mixing ratio density detection and double calibration sensor, characterized in that: The physical properties of the piezoelectric effect of quartz crystal are used to detect the mixing ratio and density of SF6 gas.

2. A sulfur hexafluoride online mixing ratio density detection and double calibration sensor according to claim 1, characterized in that: It includes a QCM detection unit built using the physical properties of the piezoelectric effect of quartz crystal.

3. A sulfur hexafluoride online mixing ratio density detection and double calibration sensor according to claim 2, characterized in that: The QCM detection unit includes a quartz crystal resonator, electrodes, a gas detection chamber, and a frequency counter. The QCM detection unit detects gases in the following ways: the electrode surface is coated with a functional material that is highly selective and sensitive to SF6 gas. When gas containing SF6 enters the gas detection chamber and comes into contact with the electrode surface, SF6 molecules are adsorbed on the electrode surface, causing the mass of the electrode surface to change, which in turn causes the frequency of the quartz crystal resonator to change. This frequency change is then measured by the frequency counter.

4. A sulfur hexafluoride online mixing ratio density detection and dual calibration sensor according to claim 3, characterized in that: The calculation of the mixing ratio and density of SF6 gas is based on a pre-established mathematical model between the frequency change of the quartz crystal resonator and the SF6 gas concentration, mixing ratio and density.

5. The sulfur hexafluoride online mixing ratio density detection and double calibration sensor according to claim 3, characterized in that: Nanofiber membrane is deposited on the electrode surface.

6. A sulfur hexafluoride online mixing ratio density detection and double calibration sensor according to claim 5, characterized in that: The nanofiber membrane includes an electrospun polyacrylic acid PAA / polyvinyl alcohol PVA composite nanofiber membrane.

7. The sulfur hexafluoride online mixing ratio density detection and double calibration sensor according to claim 2, characterized in that: It also includes a double verification unit to ensure the accuracy and reliability of the test results.

8. The sulfur hexafluoride online mixing ratio density detection and double calibration sensor according to claim 7, characterized in that: The dual calibration unit includes an internal calibration module and an external calibration module; the internal calibration module is equipped with a standard gas channel connected to a container storing standard SF6 gas of known concentration and density to calibrate the QCM detection unit; the external calibration module is equipped with an interface connected to an external standard gas source to calibrate the QCM detection unit.

9. The sulfur hexafluoride online mixing ratio density detection and dual calibration sensor according to claim 7, characterized in that: It also includes a data processing unit; the data processing unit includes a microprocessor for processing and analyzing the data collected by the QCM detection unit and the dual verification unit and a storage module for storing the data collected by the QCM detection unit and the dual verification unit.

10. A sulfur hexafluoride online mixing ratio density detection and double calibration sensor according to claim 9, characterized in that: It also includes a communication unit for enabling communication between the sensor and the remote monitoring system and a power supply unit for supplying power to the entire sensor.

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