Transfer impedance quantitative characterization method of conducted emission detection probe at high temperature

Abstract

The invention discloses a quantitative characterization method for transmission impedance of a conducted emission detection probe at high temperature. The quantitative characterization method comprises the following steps: S1, constructing an equivalent circuit model when the conducted emission detection probe tests a tested cable; s2, quantitative characterization analysis is conducted on the transmission impedance of the normal-temperature conducted emission detection probe based on equivalent circuit model analysis; and S3, carrying out quantitative characterization analysis on the transmission impedance of the high-temperature conducted emission detection probe based on equivalent circuit model analysis. According to the method, equivalent circuit modeling of the conducted emission detection probe and quantitative characterization of the transmission impedance under the high-temperature extreme working condition can be achieved, and help is provided for analysis of performance change reasons of the conducted emission detection probe and design and optimization of the high-temperature conducted emission detection probe.

Description

Technical Field

[0001] The invention relates to the field of conducted emission electromagnetic interference detection of complex electronic systems, and in particular to a method for quantitatively characterizing the transmission impedance of a conducted emission detection probe under high temperature. Background Art

[0002] With the continuous development of electronic technologies such as chips and integrated circuits, and with the trend of electronic system circuit integration, high speed and intelligence, the size of electronic systems and equipment has been continuously reduced, the bandwidth has been continuously increased, and the working spectrum density has been continuously improved. The electromagnetic compatibility problems of complex electronic systems, especially the system self-disturbance caused by conducted interference, have become increasingly prominent. In the process of working, complex electronic systems need to use a large number of cables for connection, so as to realize the communication and power transmission between different devices or components. Electromagnetic interference generates interference current on the cables through coupling and transmits it to electromagnetic sensitive devices. When the interference energy is large enough, it will affect the normal operation of sensitive devices. In many actual electromagnetic compatibility problems of complex electronic systems, connecting cables is the main reason for interference to the equipment. Therefore, in order to ensure the good electromagnetic compatibility of complex electronic systems, it is necessary to connect all external cables to the complex electronic systems and all cables should be in normal working state, so that its electromagnetic compatibility is in the most severe state for testing.

[0003] As the most commonly used detection equipment in EMC and EMI problems, the measurement accuracy of the conducted emission detection probe has a great impact on the subsequent research on EMC issues. However, the actual working environment of most cables is often not a normal temperature environment, but a more complex environment with changing temperatures, which makes it impossible to achieve a stable electromagnetic detection environment and controllable temperature. In particular, extreme high temperature conditions will have a significant impact on the measurement results of the conducted emission detection probe, mainly manifested as: the mechanical properties of the conducted emission detection probe in high temperature, high pressure, and high speed working environments are different from those in normal temperature and pressure working environments, thus affecting the measurement results, such as deformation of the internal structure, which affects the measurement results; the material parameters of the key components of the conducted emission detection probe will also change significantly under extreme high temperature conditions, thereby affecting the measurement accuracy of the conducted emission detection probe. According to the survey, most of the current research on conducted emission detection probes is applied in a relatively ideal environment. A small number of studies only consider the calibration method of the conducted emission detection probe transmission impedance changes with temperature in a darkroom environment below 50°C and with little temperature change. There are few studies on the equivalent modeling and quantitative characterization of the performance of conducted emission detection probes in actual working environments, especially under extreme high temperature conditions. It is unable to provide help for analyzing the reasons for performance changes of ordinary conducted emission detection probes and the design and optimization of high-temperature conducted emission detection probes. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for quantitatively characterizing the transmission impedance of a conducted emission detection probe under high temperature, which can realize equivalent circuit modeling and quantitative characterization of the transmission impedance of the conducted emission detection probe under extreme high temperature conditions, and provide assistance for analyzing the causes of performance changes of the conducted emission detection probe and the design and optimization of the high temperature conducted emission detection probe.

[0005] The object of the present invention is achieved through the following technical solution: A method for quantitatively characterizing the transmission impedance of a conduction emission detection probe at high temperature, comprising the following steps:

[0006] S1. Construct an equivalent circuit model when the conducted emission detection probe is used to test the cable under test;

[0007] The step S1 comprises:

[0008] The conducted emission detection probe includes a magnetic core and a winding coil wound on the magnetic core, and the magnetic core and the winding coil are encapsulated by a filling material; when the conducted emission detection probe tests the cable under test, the output of the conducted emission detection probe is connected to a test instrument for measurement. During the measurement, the cable under test is equivalent to a primary winding, and the inductance characteristic of the cable under test is represented by a first inductor L1. The current flowing through the first inductor L1 is the current flowing through the cable under test, represented by I1; the winding coil of the conducted emission detection probe is equivalent to a secondary winding, and its inductance characteristic is represented by a second inductor L2. There is a coupling relationship between the primary winding and the secondary winding due to the mutual inductance effect, and the coupling relationship is equivalent to the mutual inductance M.

[0009] The probe internal resistance is divided into two parts: coil resistance and core loss. The core loss is equivalent to a resistor r2 based on Ohm's law, and the coil resistance of the winding is expressed as a resistor r1. Therefore, the probe internal resistance is equivalent to the first resistor r, r=r1+r2;

[0010] The distributed capacitance existing on the probe winding coil is equivalent to a capacitor C connected in parallel with the second inductor L2;

[0011] The internal resistance of the test instrument is equivalent to the load at the output end of the winding, represented by the second resistor R;

[0012] Therefore, the equivalent circuit model of the conducted emission detection probe when testing the cable under test is composed of the first inductor L1, the second inductor L2, the first resistor r, the second resistor R and the capacitor C, wherein the mutual inductance between the first inductor L1 and the second inductor L2 is M;

[0013] Among them, the first end of the second inductor L2 is connected to the second end of the second inductor L2 after passing through the first resistor r and the second resistor R in sequence, and the second inductor L2 is connected in parallel with the capacitor C; the current I1 flows through the first inductor L1, and the induced current I2 is generated in the second inductor L2 through the mutual inductance effect.

[0014] S2. Quantitative characterization and analysis of the transmission impedance of the room temperature conducted emission detection probe based on the equivalent circuit model analysis;

[0015] The step S2 comprises:

[0016] S201. Set the transmission impedance Z of the conducted emission detection probe t It is defined as the ratio of the output voltage U0 across the internal resistance R of the test instrument to the measured current I1;

[0017] Based on Kirchhoff's law, the equivalent circuit model of the conducted emission detection probe is theoretically derived, and the transfer impedance calculation formula is obtained after derivation:

[0018]

[0019] S202. Analyze the transmission impedance of the conducted emission detection probe in the low frequency band (generally below 1MHZ), and ignore the probe internal resistance and distributed capacitance. The transmission impedance formula is simplified to:

[0020]

[0021] Wherein, j represents a complex unit, w represents an angular frequency, w = 2πf;

[0022] In the low frequency band, the inductive reactance generated by the second inductor L2 is very small, and the transmission impedance increases linearly with the frequency; but as the frequency increases, the inductive reactance of the second L2 gradually increases. When the frequency increases to f0, the inductive reactance is equivalent to the load R, and the transmission impedance gradually becomes flat, and the influence of frequency changes becomes smaller. According to the simplified formula of transmission impedance, the turning frequency of entering the "flat zone" of transmission impedance is f0=R / 2πL2, and the amplitude of transmission impedance is approximately

[0023] S203. In the high frequency band (generally above 1MHZ), the influence of distributed capacitance is mainly to cause the inductor L2 and its distributed capacitance C to resonate at a certain frequency f1, causing the transmission impedance to fluctuate and the conduction transmission probe to fail to work normally;

[0024] Based on the LC circuit principle, the resonant frequency calculation formula of the equivalent circuit model of the conducted emission detection probe is:

[0025]

[0026] S3. Quantitative characterization and analysis of the transmission impedance of high-temperature conducted emission detection probes based on equivalent circuit model analysis.

[0027] The step S3 comprises:

[0028] S301. Quantitative characterization of the change of inductance with temperature;

[0029] The step S301 includes:

[0030] Under high temperature conditions (extreme high temperature conditions), the magnetic permeability of the core will begin to change significantly, and the inductance is proportional to the magnetic permeability; quantitative characterization of the change in inductance with temperature:

[0031] It is known that the magnetic permeability of the core material at room temperature t1 is μ1, and it is known that the magnetic permeability of the core material at a certain high temperature t2 is μ2. is the material temperature coefficient, Equal to μ2 / μ1, it is known that the mutual inductance at room temperature is M and the winding inductance is L 2， At high temperature t2, the mutual inductance and self-inductance are characterized as and

[0032] The high temperature condition refers to a temperature greater than 40°C.

[0033] S302. Quantitatively characterize the change of probe internal resistance with temperature;

[0034] The step S302 includes:

[0035] The two parts of the probe's internal resistance, r1 and r2, change to varying degrees at high temperatures, quantitatively characterizing the change in core loss with temperature:

[0036] Knowing the loss volume density τ1 of a magnetic core material at room temperature t1 and the loss volume density τ2 at t2, the core loss temperature coefficient is =τ2 / τ1; if the core loss equivalent resistance at room temperature is known to be r2, then the core loss equivalent resistance at high temperature t2 is

[0037] The coil material is copper, and the relationship between the resistivity of copper and temperature is:

[0038]

[0039] It is known that the coil resistance at room temperature t1 is r1, then the coil resistance at high temperature t2 is

[0040] The internal resistance of the probe at high temperature is quantitatively represented as

[0041] S303. Quantitative characterization of the change of distributed capacitance with temperature;

[0042] The step S303 includes:

[0043] It is known that at room temperature t1, the dielectric constant of the filling material is ε 1，The distributed capacitance of the conducted emission detection probe is C1. At high temperature t2, the dielectric constant of the filling material is ε2. Then the coefficient of variation of the distributed capacitance with temperature is =ε2 / ε1, distributed capacitance at high temperature t2

[0044]

[0045] S304. Calculate the transmission impedance of the conducted emission detection probe at high temperature.

[0046] The step S304 includes:

[0047] Substituting the coefficients of variation of inductance, resistance and capacitance with temperature into the transmission impedance formula at room temperature, the transmission impedance formula of the conducted emission detection probe at high temperature is obtained as follows:

[0048]

[0049] The frequency at which the transfer impedance curve enters the "flat region" The resonant frequency is

[0050] The transmission impedance quantitative characterization method of the conducted emission detection probe of the present invention is to give the characterization of the flat area of ​​the transmission impedance and the frequency of entering the flat area, and taking into account the resonant frequency point (singular point), the transmission impedance will be affected by the resonance. When the difference with the flat area reaches a set value (the set value is generally 3db), the transmission impedance is invalid at this time; therefore, the resonant frequency needs to be given at the same time.

[0051] For different high-temperature extreme working conditions, t2 of the present application can be made to take different values, thereby completing the quantitative characterization of the transmission impedance under different high-temperature values.

[0052] The beneficial effects of the present invention are as follows: (1) When an alternating current passes through the measured cable, an induced current is generated on the secondary winding of the conducted emission detection probe, thereby outputting an induced voltage on the load, and then calculating the current size on the measured cable. Since the magnetic core is made of a high magnetic permeability material, the magnetic field is evenly distributed in the ring, thereby better ensuring the measurement accuracy of the conducted emission detection probe. The conducted emission detection probe is equivalently modeled by establishing an equivalent circuit. The distributed inductance, resistance, and capacitance on the conducted emission detection probe can be converted into lumped components and integrated into the circuit. Establishing an equivalent circuit model can not only replace the complex structure of the conducted emission detection probe with components in the circuit, thereby reducing the difficulty of studying the working mechanism of the conducted emission detection probe; at the same time, since the conducted emission detection probe is affected by parasitic parameters, and the actual distributed parameters cannot be directly obtained by analytical calculation, it is necessary to simplify it into a single lumped component to intuitively reflect its influence on the use of the conducted emission detection probe. By establishing an equivalent circuit model, the working mechanism and coupling mechanism of the conducted emission detection probe can be effectively analyzed preliminarily, providing theoretical support for subsequent steps.

[0053] (2) The present invention can directly characterize the change of the transmission impedance of the conducted emission detection probe with temperature, and provide theoretical and technical support for analyzing the causes of performance changes of ordinary conducted emission detection probes and the design and optimization of high-temperature probes. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a flow chart of the method of the present invention;

[0055] Figure 2 It is a schematic diagram of an equivalent circuit model of a conducted emission detection probe of the present invention;

[0056] Figure 3 This is a schematic diagram of the probe transmission impedance frequency response curve when the distributed capacitance and the probe internal resistance are not considered;

[0057] Figure 4 This is a schematic diagram of the probe transmission impedance frequency response curve when only the probe internal resistance is considered;

[0058] Figure 5 Schematic diagram of the probe transmission impedance frequency response curve when the probe internal resistance and distributed capacitance are considered. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0060] like Figure 1 As shown, a method for quantitatively characterizing the transmission impedance of a conducted emission detection probe at high temperature comprises the following steps:

[0061] S1. Construct an equivalent circuit model when the conducted emission detection probe is used to test the cable under test;

[0062] The cable through which the conducted emission detection probe passes is used as the primary winding. The tested current passes through the cable. During operation, the cable may have parasitic capacitance with the secondary winding (the coil winding of the conducted emission detection probe), and there is capacitive coupling between the windings. However, since the cable directly passes through the detection hole of the conducted emission detection probe, the number of turns is 1 turn, the coupling area between the cable and the conducted emission detection probe is limited, the spacing between it and the winding is usually large, and the conducted emission detection probe is filled with insulating materials with a low dielectric constant. Therefore, there is almost no parasitic capacitance between the primary and secondary windings. At the same time, since the cable is generally excited by a sinusoidal constant current source when simulating the conducted emission detection probe, the resistance on the cable does not affect the simulation results. Therefore, when establishing a circuit model for the conducted emission detection probe to analyze the working mechanism, the primary winding of the conducted emission detection probe can be represented by the inductor element L1. For the secondary winding, since the winding coil is usually 7-8 turns and is tightly wound on the magnetic core, it is necessary to consider the influence of its distributed parameters on the transmission impedance. Since there is mutual inductance between the windings, the secondary winding can be equivalent to the inductor L2. In addition, the coil is usually wound with metal material, so the coil resistance can be regarded as part of the coil internal resistance.

[0063] During the operation of the magnetic core, part of the magnetic energy of the magnetic core is converted into heat energy due to the core loss. Therefore, the core loss can be equivalent to a part of the internal resistance r of the conducted emission detection probe in series with the self-inductance L2 through Ohm's law. The probe internal resistance r is mainly composed of two parts: coil resistance r1 and core loss r2.

[0064] At the same time, there is distributed capacitance between the conduction emission detection probe winding and itself and other components. Due to the influence of high-frequency skin effect, the copper wire current is mainly distributed on the outer surface of the copper wire (the wire diameter is greater than the skin depth). Therefore, the winding coil can be regarded as a multi-layer plate for co-directional transmission. Each turn will form an inter-plate capacitance (inter-turn capacitance) with the previous and next turns, which is evenly distributed on the surface of the wire.

[0065] The total inter-turn capacitance can be considered as the capacitance between N single-turn coils in parallel:

[0066]

[0067] The inter-turn capacitance can be regarded as the parallel connection of multiple single-turn capacitors. Therefore, if other parameters remain unchanged and the number of turns increases, the inter-turn capacitance increases, resulting in a decrease in the resonant frequency and a decrease in the transmission impedance. Between the winding and the core, due to the decrease in the resistivity of the core in the high-frequency band, the proportion of eddy current loss in the core loss increases, and the eddy current on the surface of the core causes parasitic capacitance between the core and the coil winding. When the frequency increases, the resistivity of the ferrite decreases, and the core can no longer be regarded as an insulator. Eddy currents will exist on the surface of the core. Therefore, when the eddy current loss increases, the size of the parasitic capacitance between the core and the winding cannot be ignored, and the transmission impedance and resonant frequency of the conducted emission detection probe will also be affected.

[0068] Therefore, according to the inductor parasitic parameter model, the distributed capacitance of the conducted emission detection probe can be regarded as a capacitive element, which is connected in parallel with the winding inductance L2.

[0069] Generally speaking, the output of the conducted emission detection probe needs to be connected to an impedance analyzer or other measuring equipment to complete the measurement of the cable current. The internal resistance of the test instrument is specified to be 50Ω, so in the circuit model, a 50Ω resistor R needs to be connected to the output end of the secondary winding as the internal resistance of the measuring instrument. The equivalent circuit model of the conducted emission detection probe is constructed, such as Figure 2 shown.

[0070] S2. Quantitative characterization and analysis of the transmission impedance of the room temperature conducted emission detection probe based on the equivalent circuit model analysis;

[0071] According to Kirchhoff's law, a series of theoretical derivations can be made on the transmission impedance of the equivalent circuit model, and finally the calculation formula for the transmission impedance of the conducted emission detection probe is obtained:

[0072] jwMI1=jwL2I2+rI2+ZI2 (2)

[0073]

[0074] Where: M is the mutual inductance between the conducted emission detection probe and the cable under test; L1 is the self-inductance of the cable under test; L2 is the self-inductance of the winding coil (distributed inductance); r is the internal resistance of the conducted emission detection probe; C is the distributed capacitance of the coil; R is the instrument load (generally 50Ω); U0 is the output voltage; Z is the total impedance within the dotted line.

[0075] From formula (5), we can see that the transmission impedance Z t It is related to the mutual inductance M, distributed capacitance C between the primary and secondary windings, the internal resistance r of the conducted emission detection probe, and the operating frequency w. Therefore, the transmission impedance is related to the measured current frequency, the magnetic permeability of the magnetic core, the number of coil turns, the coil distribution parameters and other parameters.

[0076] In the low frequency band, the distributed capacitance and probe internal resistance are negligible compared to the inductance and load. The distributed capacitance and probe internal resistance can be ignored. At this time, the transmission impedance of the conducted emission detection probe can be simplified to

[0077]

[0078] Assume that the primary current amplitude of the conducted emission detection probe remains unchanged. The general formula for the inductance of the winding is:

[0079]

[0080] Where L is the inductance; μ is the magnetic permeability in a vacuum; N is the number of turns of the coil; A e It represents the cross-sectional area of ​​the magnetic core; l represents the length of the magnetic circuit of the magnetic core.

[0081] At low frequencies, the inductive reactance generated by the self-inductance L2 is very small and can be ignored. The transmission impedance can be regarded as increasing linearly with the frequency in the low frequency band. Therefore, as the current frequency increases, the induced voltage generated on the load increases by 20dB per decade, but as the frequency increases, the inductive reactance gradually increases. When the frequency point f0 increases to the point where the inductive reactance is equal to the load impedance, the inductive reactance cannot be ignored. The transmission impedance changes with frequency as shown in Figure 3 As shown. When the frequency point f0 is reached, since the inductive reactance is large enough and the frequency has little effect on the self-inductive reactance, the transmission impedance of the conducted emission detection probe is almost unchanged and the output voltage becomes flat. According to formula (6), the frequency f0 = R / 2πL2, the transmission impedance Z t ≈MR / L2.

[0082] When the internal resistance of the conducted emission detection probe is considered, f0 = (R + r) / 2πL2. The transmission impedance remains unchanged, and r increases. It can be seen that f0 shifts to the high frequency region, such as Figure 4 shown.

[0083] The distributed capacitance of the conducted emission detection probe is mainly composed of the capacitance between turns and the capacitance between the magnetic core. It is generally in the pF range. Compared with the inductance and load, the distributed capacitance can be ignored at low frequencies. Therefore, the influence of the distributed capacitance on the conducted emission detection probe can be ignored at low frequencies. However, the influence of the distributed capacitance at high frequencies, especially after the resonant frequency, cannot be ignored. The equivalent parallel capacitance effect of the distributed capacitance of the conducted emission detection probe will cause the inductance and its distributed capacitance to resonate at a certain frequency as the frequency continues to increase. This frequency point is the self-resonant frequency point. like Figure 5 shown.

[0084] S3. Quantitative characterization and analysis of the transmission impedance of high-temperature conducted emission detection probes based on equivalent circuit model analysis.

[0085] There is a proportional relationship between inductance L and magnetic permeability μ. The greater the magnetic permeability, the greater the inductance value in theory. In other words, for the same coil parameters (number of turns, cross-sectional area, length), when a material with a higher magnetic permeability is used as the magnetic core, the resulting inductance value will be larger and the inductive reactance will increase. Therefore, changes in magnetic permeability will directly affect the transmission impedance of the conducted emission detection probe. Temperature is one of the main factors affecting changes in magnetic permeability. In extreme high-temperature conditions, magnetic permeability will have a Curie point temperature. Magnetic permeability will change dramatically near the Curie point temperature. Therefore, in order to characterize the changes brought about by temperature, the self-inductance and mutual inductance of the probe in the circuit can be multiplied by a material temperature coefficient in order to consider the temperature effect during calculation. The temperature coefficient is the ratio of the magnetic permeability at room temperature to the magnetic permeability at high temperature.

[0086] For the core loss, the core loss temperature coefficient can be obtained based on the ratio of the core loss at different temperatures to the core loss at room temperature. Ohm's law equates the core loss to resistance r2.

[0087] For the coil resistance r1, the material properties of copper will change with temperature, thereby changing the size of the distributed resistance, which in turn affects the temperature distribution of the conduction emission detection probe in a low temperature environment. This can be achieved by modifying the metal conductivity temperature variation coefficient The coil resistance at the corresponding temperature can be preliminarily determined, which ultimately affects the transmission impedance. The relationship between the resistivity of copper and temperature is:

[0088]

[0089] Where σ is the conductivity, in Siemens per meter (S / m); pre is the conductivity at room temperature, usually 5.8×10 7 (S / m); t is the current temperature; t pre The reference temperature is 20°C.

[0090] The internal resistance of the probe under high temperature extreme working conditions can be recorded as

[0091]

[0092] The influence of temperature on the distributed capacitance of the coil is mainly due to the dielectric constant of the insulating paint and the coil structure. Since the coil has a certain rigidity and a small number of turns, the internal spacing of the probe rarely changes significantly due to high temperature. The distributed capacitance is mainly affected by the change of the dielectric constant with temperature. The ratio of the dielectric constant change can be determined based on the material dielectric constant temperature curve, and the distributed capacitance change coefficient is is (1+Δε).

[0093]

[0094] When analyzing the measurement results of the conducted emission detection probe at unconventional temperatures, the key parameters that affect the transmission impedance of the probe can be found out based on the changes in various parameters. When designing test samples, this equivalent modeling and quantitative characterization method can be used to quickly obtain the key performance indicators of the high-temperature conducted emission detection probe. This provides a simple and efficient quantitative characterization and analysis method for the preliminary design of the high-temperature conducted emission detection probe and the rapid location of the causes of performance changes.

[0095] The mutual inductance M of the existing conducted emission detection probe is 0.64uH, and the measured coil inductance L2 is 3.64uH. When the temperature is 90℃, the magnetic permeability increases to 1.3 times the original magnetic permeability. At this time, the coil resistance at room temperature 20℃ is 0.00016Ω, and the equivalent resistance r1 at 90℃ is 0.00016×(1+0.0043×(90-20))=0.0002082Ω. The current measured by the probe terminal oscilloscope is 0.4mA. The core loss is interpolated according to the manufacturer's body loss density at different temperatures to obtain the core temperature coefficient at 90℃ Multiplying by the core loss at room temperature, the core loss at 90°C is 0.13mW, the equivalent resistance r1 is 0.0008125Ω, and the instrument load is 50Ω. According to the resonant frequency feedback measured at room temperature, the distributed capacitance is 0.02pF. Usually, the coating of polyester enameled wire has a dielectric constant of about 3.5 at room temperature and about 3.15 at 90°C. Its capacitance variation coefficient is 0.9, and the capacitance at 90°C is about 0.018pF.

[0096] At low frequency, since the internal resistance of the probe is negligible, f0=10.57MHz, the transmission impedance is about 8.791Ω, i.e. 18.88dB; the resonant frequency f1=567.6MHz, the construction of the equivalent circuit model and the quantitative characterization analysis method of the conducted emission detection under extreme high temperature conditions can quickly calculate the transmission impedance and working frequency band of the conducted emission monitoring probe under extreme high temperature conditions, and the preliminary analysis of the performance of the conducted emission monitoring probe under extreme high temperature conditions has a more intuitive quantitative characterization analysis.

[0097] The equivalent circuit modeling and quantitative characterization method proposed in the present invention can help analyze the causes of performance changes of common conducted emission detection probes and the design and optimization of high-temperature conducted emission detection probes. The change of the transmission impedance of the conducted emission detection probe with temperature can be simply and directly equivalent to the change of the circuit concentrated parameter, and a quantitative characterization and analysis method for the performance parameters of the high-temperature conducted emission detection probe is given.

[0098] The above description shows and describes a preferred embodiment of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. And the changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe, characterized in that: The following steps are involved: S1. Construct an equivalent circuit model when the conducted emission detection probe is used to test the cable under test; S2. Quantitative characterization and analysis of the transmission impedance of the room temperature conducted emission detection probe based on the equivalent circuit model analysis; S3. Quantitative characterization and analysis of the transmission impedance of high-temperature conducted emission detection probes based on equivalent circuit model analysis.

2. The method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe according to claim 1, characterized in that: The step S1 comprises: Assume that the conducted emission detection probe includes a magnetic core and a winding coil wound on the magnetic core, and the magnetic core and the winding coil are encapsulated by a filling material; when the conducted emission detection probe tests the cable under test, the output of the conducted emission detection probe is connected to a test instrument for measurement. During the measurement, the cable under test is equivalent to a primary winding, and the inductance characteristic of the cable under test is represented by a first inductor L1. The current flowing through the first inductor L1 is the current flowing through the cable under test, which is represented by I1; the winding coil of the conducted emission detection probe is equivalent to a secondary winding, and its inductance characteristic is represented by a second inductor L2. There is a coupling relationship between the primary winding and the secondary winding due to the mutual inductance effect, and the coupling relationship is equivalent to the mutual inductance M. The probe internal resistance is divided into two parts: coil resistance and core loss. The core loss is equivalent to a resistor r2 based on Ohm's law, and the coil resistance of the winding is expressed as a resistor r1. Therefore, the probe internal resistance is equivalent to the first resistor r, r=r1+r2; The distributed capacitance existing on the probe winding coil is equivalent to a capacitor C connected in parallel with the second inductor L2; The internal resistance of the test instrument is equivalent to the load at the output end of the winding, represented by the second resistor R; Therefore, the equivalent circuit model of the conducted emission detection probe when testing the cable under test is composed of the first inductor L1, the second inductor L2, the first resistor r, the second resistor R and the capacitor C, wherein the mutual inductance between the first inductor L1 and the second inductor L2 is M; Among them, the first end of the second inductor L2 is connected to the second end of the second inductor L2 after passing through the first resistor r and the second resistor R in sequence, and the second inductor L2 is connected in parallel with the capacitor C; the current I1 flows through the first inductor L1, and the induced current I2 is generated in the second inductor L2 through the mutual inductance effect.

3. The method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe according to claim 1, characterized in that: The step S2 comprises: S201. Set the transmission impedance Z of the conducted emission detection probe t It is defined as the ratio of the output voltage U0 across the internal resistance R of the test instrument to the measured current I1; Based on Kirchhoff's law, the equivalent circuit model of the conducted emission detection probe is theoretically derived, and the transfer impedance calculation formula is obtained after derivation: Wherein, j represents a complex unit, w represents an angular frequency, w = 2πf; S202. Analyze the transmission impedance of the low-frequency conducted emission detection probe. Ignoring the probe internal resistance and distributed capacitance, the transmission impedance formula is simplified to: In the low frequency band, the inductive reactance generated by the second inductor L2 is very small, and the transmission impedance increases linearly with the frequency; but as the frequency increases, the inductive reactance of the second L2 gradually increases. When the frequency increases to f0, the inductive reactance is equivalent to the load R, and the transmission impedance gradually becomes flat, and the influence of frequency changes becomes smaller. According to the simplified formula of transmission impedance, the turning frequency of entering the "flat zone" of transmission impedance is f0=R / 2πL2, and the amplitude of transmission impedance is approximately S203. As the frequency increases, the influence of the distributed capacitance mainly causes the inductor L2 and its distributed capacitance C to resonate at a certain frequency f1, causing the transmission impedance to fluctuate and the conduction transmission probe to fail to work normally; Based on the LC circuit principle, the resonant frequency calculation formula of the equivalent circuit model of the conducted emission detection probe is:

4. The method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe according to claim 1, characterized in that: The step S3 comprises: S301. Quantitative characterization of the change of inductance with temperature; S302. Quantitatively characterize the change of probe internal resistance with temperature; S303. Quantitative characterization of the change of distributed capacitance with temperature; S304. Calculate the transmission impedance of the conducted emission detection probe at high temperature.

5. The method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe according to claim 4, characterized in that: The step S301 includes: Under high temperature conditions, the magnetic permeability of the core will begin to change significantly, and the inductance is proportional to the magnetic permeability; quantitative characterization of the change in inductance with temperature: It is known that the magnetic permeability of the core material at room temperature t1 is μ1, and it is known that the magnetic permeability of the core material at a certain high temperature t2 is μ2. is the material temperature coefficient, Equal to μ2 / μ1, it is known that the mutual inductance at room temperature is M and the winding inductance is L 2， At high temperature t2, the mutual inductance and self-inductance are characterized as and The high temperature condition refers to a temperature greater than 40°C.

6. The method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe according to claim 4, characterized in that: The step S302 includes: The two parts of the probe's internal resistance, r1 and r2, change to varying degrees at high temperatures, quantitatively characterizing the change in core loss with temperature: Knowing the loss volume density τ1 of a magnetic core material at room temperature t1 and the loss volume density τ2 at t2, the core loss temperature coefficient is =τ2 / τ1; if the core loss equivalent resistance at room temperature is known to be r2, then the core loss equivalent resistance at high temperature t2 is The coil material is copper, and the relationship between the resistivity of copper and temperature is: It is known that the coil resistance at room temperature t1 is r1, then the coil resistance at high temperature t2 is The internal resistance of the probe at high temperature is quantitatively represented as 7. The method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe according to claim 4, characterized in that: The step S303 includes: It is known that at room temperature t1, the dielectric constant of the filling material is ε 1， The distributed capacitance of the conducted emission detection probe is C1. At high temperature t2, the dielectric constant of the filling material is ε2. Then the coefficient of variation of the distributed capacitance with temperature is =ε2 / ε1, distributed capacitance at high temperature t2 8. The method for quantitatively characterizing the transmission impedance of a high temperature conduction emission detection probe according to claim 4, characterized in that: The step S304 includes: Substituting the coefficients of variation of inductance, resistance and capacitance with temperature into the transmission impedance formula at room temperature, the transmission impedance formula of the conducted emission detection probe at high temperature is obtained as follows: The frequency at which the transfer impedance curve enters the "flat region" The resonant frequency is

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