Method for measuring rotation speed of arc root of arc heater based on B-dot probe

Abstract

A method for measuring the rotation speed of an arc root of an arc heater based on a B-dot probe comprises the steps of measurement of voltage signals and arc current generated in the B-dot probe, low-pass and high-pass filtering processing of voltage and current signals, differential processing of the current signals, and mathematical operation and Fourier transform of the voltage and current signals. Strong interference influence generated by current fluctuation caused by self reasons of a power supply system can be removed from an original signal measured by a B-dot probe, so that a change rule of a voltage signal caused by rotation of an arc root of an electric arc can be accurately identified, and then the rotation speed of the arc root can be accurately and quickly obtained. The method is simple, reliable, high in efficiency and wide in application range.

Description

Technical Field

[0001] The invention relates to a method for measuring the arc root rotation speed of an arc heater based on a B-dot probe, and belongs to the field of arc heater performance research and design. Background Art

[0002] The arc heater can simulate the aerodynamic thermal environment of the re-entry vehicle and is the most important ground simulation test equipment for the screening and assessment of aircraft thermal protection materials. It has an extremely high heat flux density (~10 9 -10 10 W / m 2 The electrode ablation caused by the arc root's attachment and movement on the electrode surface is the core problem that limits the performance and life of the arc heater, and has become the main factor restricting the performance and service life of the arc heater. Increasing the speed of the arc root rotation through magnetic field and rotating airflow is an effective means to reduce electrode ablation. Accurately measuring the arc root rotation speed is crucial for regulating and evaluating the electrode life.

[0003] At present, the commonly used methods for measuring the rotation speed of the arc root mainly include the arc mark method, the photoelectric conversion method and the high-speed imaging method. The arc mark method is to measure the arc ablation marks on the electrode surface under short pulse current to obtain the movement speed of the arc (actually the arc root) on the electrode surface, but this method can only be used under the conditions of small current and smooth electrode surface. The photoelectric conversion method converts the light emitted by the arc into an electrical signal, thereby recording the moment when the arc passes through the optical probe each time. Chu-Hyun and Geun-Hie evenly arranged photodiodes in the annular electrode of the rotating arc switch, and obtained that the arc movement speed was 1.2km / s under the decaying current wave with a peak value of 160kA. Li and Chen et al. used an optical fiber array to collect the light emitted by the arc, which not only obtained the movement speed of the arc, but also the approximate shape of the arc. The accuracy of this method is restricted by the response speed of the photoelectric conversion device, and the frequency of the signal to be measured and the response speed of the device must be considered comprehensively. Moreover, for the diffuse arc plasma, the spatial resolution of the measurement is not high. The shape of the arc can also be directly obtained during the measurement of the arc speed by the high-speed imaging method. For example, Szente used a shooting rate of 5000 frames / s to study the influence of the cathode surface on the arc movement speed of a 100A DC arc with an arc burning time of 30 minutes in various gas media. Painter et al. used a high-speed camera with a frame rate of 10800fps to study the arc morphology of the anode area of ​​a high-voltage laminated heater under different electrical parameters, magnetic parameters and heater structures. The high-speed camera used by Kil-Soo et al. was 27000 frames / s, and was used to shoot the movement of the arc in a vacuum-encapsulated rotary arc switch. The peak current was 25kA, and the pulse width was only 520μs, and the arc movement speed was about 0.6~1km / s. Christopher and Sheeley et al. used a high-speed camera system to observe and measure the arc attachment area, arc shunt phenomenon and arc speed of the H3 high-voltage laminated arc heater in the United States. However, high-speed cameras generally have limited memory, and the acquisition time in high-speed acquisition mode is relatively short, which cannot meet the needs of collecting all image information from arc starting to arc stabilization time of the heater; parameters such as exposure time and frame rate of high-speed cameras need to be accurately set, otherwise useful information cannot be obtained; high-speed cameras cannot capture the movement of the arc near the front electrode far away from the rear end cover of the heater; in addition, this method requires a glass observation window to be set at the rear end cover of the arc heater. When the operating pressure of the arc heater is high, the observation window is prone to breakage. Summary of the invention

[0004] The technical problem solved by the present invention is: in view of the drawbacks of the traditional arc root measurement method in the current prior art, a method for measuring the arc root rotation speed of an arc heater based on a B-dot probe is proposed.

[0005] The present invention solves the above technical problems by the following technical solutions:

[0006] A method for measuring the arc root rotation speed of an arc heater based on a B-dot probe, comprising:

[0007] The voltage signal B1 of the arc heater and the current signal H1 of the input cable are collected using a B-dot probe;

[0008] Perform high-pass filtering and low-pass filtering on the voltage signal B1 and the current signal H1 to obtain a filtered voltage signal B2 and a filtered current signal H2;

[0009] Collect the induced voltage in the B-dot probe;

[0010] Performing differentiation processing on the filtered current signal H2 to obtain a differentiated current signal H3;

[0011] The differential coefficient is calculated according to the current signal H3 after differential processing and the voltage signal B2 after filtering processing at the same time;

[0012] Calculate the probe current fluctuation induced voltage signal B3 according to the differential coefficient and the filtered voltage signal B2;

[0013] The probe arc rotation induced voltage B4 is calculated using the filtered voltage signal B2 and the probe induced voltage signal B3 at the same time;

[0014] Perform Fourier transform on the probe arc rotation induced voltage B4 to obtain the rotation speed of the arc root.

[0015] The arc heaters include laminated heaters, segmented heaters, and thick laminated heaters, and all types of arc heaters are suitable for B-dot probe acquisition and measurement tasks.

[0016] The voltage signal B1 of the arc heater and the current signal H1 of the input cable are collected synchronously by the B-dot probe, and the collection frequency range is set to: [0.5MHz, 20MHz].

[0017] The B-dot probe is a standard cylindrical structure probe. During the installation of the B-dot probe, the cylindrical axis of the B-dot probe is ensured to be strictly parallel to the radial plane of the electrode to be measured to ensure measurement accuracy.

[0018] The B-dot probe measures current through a Hall sensor provided inside the probe, and the maximum current range of the Hall sensor is set within the following range:

[0019] 1.5*maximum arc current ≤ maximum range of Hall sensor ≤ 2.5*maximum arc current.

[0020] The probe length design range of the B-dot probe is:

[0021] 1.0≤B-dot probe length / diameter≤2.0, 0.1≤B-dot probe length / electrode diameter≤0.5;

[0022] High-pass filtering and low-pass filtering are achieved through finite impulse response filters, with the high-pass cutoff frequency set to 5-10 Hz and the low-pass cutoff frequency set to 500-1000 Hz.

[0023] When the filtered current signal H2 is differentiated, the differentiation order is set to 5-10 and the filtering frequency is set to 50-100 kHz.

[0024] The frequency resolution range used in the Fourier transform is 0.2 Hz≤frequency resolution≤1 Hz, the averaging method uses energy averaging, and the overlap rate is set to 90%.

[0025] During the calculation of the differential coefficient, the probe current fluctuation induced voltage signal B3, and the probe arc rotation induced voltage B4, the collected data are data at the same time or within the same time range;

[0026] The data time length of the time range is set to: 1 / data time length ≤ 0.8*frequency resolution.

[0027] The method for calculating the differential coefficient using the current signal H3 after differential processing and the voltage signal B2 after filtering processing is:

[0028] a=Σ(H3 i / B2 i ) i＝1…n / n

[0029] Where a is the differential coefficient and n is the number of collected data.

[0030] The advantages of the present invention compared with the prior art are:

[0031] (1) The present invention provides a method for measuring the arc root rotation speed of an arc heater based on a B-dot probe. Based on the basic principle that the periodically changing magnetic field generated in the space during the radial rotation of the arc will generate an induced voltage in the B-dot sensor, a signal processing method is proposed to eliminate interference signals and accurately identify the arc root rotation characteristic frequency parameters. The arc root rotation speed is measured quickly and accurately by combining a simple B-dot probe with the proposed signal processing method, which greatly improves the accuracy and efficiency of the arc root rotation speed measurement of the arc heater under different operating environments.

[0032] (2) The test equipment of the present invention is simple, low-cost and easy to install. During the test, only a B-dot probe and a Hall sensor are required, wherein the B-dot probe can be directly bonded to the excitation coil using plasticine. The measurement method can complete the measurement of the arc root rotation speed for a long time, and can monitor the dynamic change law of the arc root rotation in different time periods. At the same time, the applicable scope of the measurement method is independent of the operating parameters of the arc heater. The arc heater can be used normally under high arc chamber pressure (≥5MPa) and high current (≥2000A) conditions;

[0033] (3) The present invention has a wide range of applications and can be used to measure the arc root rotation speed of a laminated heater, a segmented heater or a thick laminated heater, and the arc root rotation speed at the front and rear electrodes can be measured. The measurement method involved is scientific and reasonable with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flow chart of a method for measuring the arc root rotation speed of an arc heater based on a B-dot probe provided by the present invention;

[0035] Figure 2 A typical arc heater electrode structure provided by the present invention. DETAILED DESCRIPTION

[0036] A method for measuring the rotation speed of the arc root of an arc heater based on a B-dot probe includes the measurement of the voltage signal and arc current generated in the B-dot probe, low-pass and high-pass filtering of the voltage and current signals, differential processing of the current signal, mathematical operations of the voltage and current signals, and Fourier transformation. The method can remove the strong interference caused by the current fluctuation caused by the power supply system itself from the original signal measured by the B-dot probe and accurately identify the change law of the voltage signal caused by the rotation of the arc root, and then accurately and quickly obtain the rotation speed of the arc root. The method is simple, reliable, efficient, and has a wide range of applications.

[0037] The following is further described in conjunction with the accompanying drawings and preferred embodiments of the specification:

[0038] In the current embodiment, if Figure 1 The following is the process of measuring the arc heater arc root rotation speed:

[0039] The method comprises the measurement of the voltage signal and arc current generated in the B-dot probe (1), low-pass and high-pass filtering of the voltage and current signals (2), differential processing of the current signal (3), mathematical operation of the voltage and current signals (4) and Fourier transformation (5).

[0040] Measurement of the voltage signal and arc current generated in the B-dot probe (1): The B-dot probe collects the voltage signal B1; the Hall sensor collects and measures the current signal H1 on the cable connected to the arc heater.

[0041] Low-pass and high-pass filtering of voltage and current signals (2): The same processing method is used to perform high-pass filtering and low-pass filtering on B1 and H1 in (1) to obtain B2 and H2.

[0042] Current signal differential processing (3): The arc heater has a large operating current. The fluctuation of its own value will generate an obvious voltage signal in the B-dot probe and cause superimposed interference to the voltage signal generated by the arc root rotation. The induced voltage generated by the arc current fluctuation in the B-dot probe is:

[0043] ε=-NAμ 0 / 2πr*dI / dt

[0044] Where ε is the induced voltage, N is the number of turns of the probe coil, A is the cross-sectional area of ​​the probe coil, r is the distance between the probe and the electrode axis, μ 0 is the vacuum permeability, and I is the arc current. Differentiate H2 in (2) to obtain dI / dt, which is H3.

[0045] Mathematical operation of voltage and current signals (4): Divide and add all the data points of H3 and B2 at the same time and take the average value a, that is:

[0046] a=∑(H3 i / B2 i ) i＝1…n / n

[0047] From (3), it can be seen that when the arc current fluctuates rapidly with time, the induced potential generated in the B-dot probe is very large, much larger than the induced voltage generated in the B-dot probe by the rotation of the arc root. B2 is multiplied by the coefficient a to obtain B3, that is, B2*a=B3, which is assumed to be the induced voltage generated in the B-dot probe by the arc current fluctuation; B4 is subtracted from all data points of B2 and B3 at the same time, that is, B2-B3=B4, which is considered to be the induced voltage generated in the B-dot probe by the rotation of the arc root.

[0048] Fourier transform (5): B4 is subjected to Fourier (FFT) transform to obtain the characteristic frequency f on the frequency domain curve; the rotation speed of the arc root v = π*d*f, where d is the electrode diameter;

[0049] The specific design is:

[0050] The types of arc heaters to which the example method is applicable include, but are not limited to, stack heaters, segmented heaters, and thick stack heaters.

[0051] In the measurement of the voltage signal and arc current generated in the B-dot probe (1), the Hall sensor and the B-dot probe need to be collected synchronously, with a collection frequency of 0.5MHz≤≤20MHz.

[0052] Measurement of the voltage signal and arc current generated in the B-dot probe (1) The B-dot probe preferably adopts a standard cylindrical structure, and the cylindrical axis is strictly parallel to the radial plane of the electrode during installation.

[0053] The voltage signal generated in the B-dot probe and the arc current measurement (1) use 1.5*maximum arc current ≤ Hall sensor maximum range ≤ 2.5*maximum arc current.

[0054] The voltage signal and arc current generated in the B-dot probe are measured (1) where 1.0≤B-dot probe length / diameter≤2.0, 0.1≤B-dot probe length / electrode diameter≤0.5.

[0055] The filtering method in the low-pass and high-pass filtering processing (2) of the voltage and current signals is preferably a finite impulse response filter (FIR), with a high-pass cutoff frequency of 5-10 Hz and a low-pass cutoff frequency of 500-1000 Hz.

[0056] In the current signal differential processing (3), the differential order is 5-10, the low-pass filter mode, and the low-pass frequency is 50-100kHz.

[0057] In the voltage and current signal mathematical operation (4), the data points of operation 1 are preferably all data points within the taken time period, or data points at the same interval, where the number of time points is ≥ 0.1*all data points.

[0058] In the voltage and current signal mathematical operation (4), the data involved in operation 2 and operation 3 are all data points within the selected time period.

[0059] In Fourier transform (5), the frequency resolution is 0.2 Hz ≤ ≤ 1 Hz, the averaging method is preferably energy averaging, and the overlap rate is 90%.

[0060] The voltage and current signal mathematical operation (4) selected is 1 / data time length ≤ 0.8*frequency resolution.

[0061] This embodiment is directed to the following: 1. electrode housing 2. cooling water inlet 3. excitation coil 4. insulation sleeve 5. cooling water outlet 6. electrode Figure 2The arc heater shown utilizes a simple B-dot probe combined with the proposed signal processing method to quickly and accurately measure the arc root rotation speed, which greatly improves the accuracy and efficiency of the arc heater in measuring the arc root rotation speed under different operating environments.

[0062] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

[0063] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for measuring the arc root rotation speed of an arc heater based on a B-dot probe, characterized in that include: The voltage signal B1 of the arc heater and the current signal H1 of the input cable are collected using a B-dot probe; Perform high-pass filtering and low-pass filtering on the voltage signal B1 and the current signal H1 to obtain a filtered voltage signal B2 and a filtered current signal H2; Collect the induced voltage in the B-dot probe; Performing differentiation processing on the filtered current signal H2 to obtain a differentiated current signal H3; The differential coefficient is calculated according to the current signal H3 after differential processing and the voltage signal B2 after filtering processing at the same time; Calculate the probe current fluctuation induced voltage signal B3 according to the differential coefficient and the filtered voltage signal B2; The probe arc rotation induced voltage B4 is calculated using the filtered voltage signal B2 and the probe induced voltage signal B3 at the same time; Perform Fourier transform on the probe arc rotation induced voltage B4 to obtain the rotation speed of the arc root.

2. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: The arc heaters include laminated heaters, segmented heaters, and thick laminated heaters, and all types of arc heaters are suitable for B-dot probe acquisition and measurement tasks.

3. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: The voltage signal B1 of the arc heater and the current signal H1 of the input cable are collected synchronously by the B-dot probe, and the collection frequency range is set to: [0.5MHz, 20MHz].

4. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: The B-dot probe is a standard cylindrical structure probe. During the installation of the B-dot probe, the cylindrical axis of the B-dot probe is ensured to be strictly parallel to the radial plane of the electrode to be measured to ensure measurement accuracy.

5. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: The B-dot probe measures current through a Hall sensor provided inside the probe, and the maximum current range of the Hall sensor is set within the following range: 1.5*maximum arc current ≤ maximum range of Hall sensor ≤ 2.5*maximum arc current.

6. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: The probe length design range of the B-dot probe is: 1.0≤B-dot probe length / diameter≤2.0, 0.1≤B-dot probe length / electrode diameter≤0.5; High-pass filtering and low-pass filtering are achieved through finite impulse response filters, with the high-pass cutoff frequency set to 5-10 Hz and the low-pass cutoff frequency set to 500-1000 Hz.

7. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: When the filtered current signal H2 is differentiated, the differentiation order is set to 5-10 and the filtering frequency is set to 50-100 kHz.

8. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: The frequency resolution range used in the Fourier transform is 0.2 Hz≤frequency resolution≤1 Hz, the averaging method uses energy averaging, and the overlap rate is set to 90%.

9. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: During the calculation of the differential coefficient, the probe current fluctuation induced voltage signal B3, and the probe arc rotation induced voltage B4, the collected data are data at the same time or within the same time range; The data time length of the time range is set to: 1 / data time length ≤ 0.8*frequency resolution.

10. The method for measuring the arc root rotation speed of an arc heater based on a B-dot probe according to claim 1, characterized in that: The method for calculating the differential coefficient using the current signal H3 after differential processing and the voltage signal B2 after filtering processing is: a=Σ(H3 i / B2 i )i=1… / n Where a is the differential coefficient and n is the number of collected data.

Images