A method for generating and measuring low static spark energy

Abstract

The present invention discloses a method for generating and measuring low static spark energy. The main process of the method is: under a given charging voltage condition, test and obtain the corresponding discharge voltage of different energy storage capacitors; calculate the parasitic capacitance of the front and rear stages of the circuit according to the change of charging and discharging voltage; select different charging voltages and energy storage capacitors for spark discharge, and test and obtain the current waveform of the spark generating circuit; calculate the discharge end voltage waveform according to the current waveform and parasitic capacitance; calculate the total discharge energy, calculate the resistance offset energy, and subtract the two to obtain the spark energy; fit and establish the relationship between spark energy and charging voltage. The present invention reduces the spark energy by resistor voltage division, and at the same time avoids the spark energy loss and signal waveform phase error caused by probe contact, improves the accuracy of static spark energy generation and testing, and provides support for the minimum ignition energy test of sensitive flammable gas and dust cloud.

Description

Technical Field

[0001] The invention relates to a method for generating and measuring low static spark energy. Background Art

[0002] The minimum ignition energy indicates the lowest spark energy that can cause the ignition of the measured substance. It is an important parameter for evaluating the explosion hazard of combustible gases and dusts, and plays an important reference role in the explosion prevention and suppression design in related industrial production, transportation, and processing. Studies have shown that the minimum ignition energy of many combustible gases and dust clouds formed by nano-particle powders in the air is less than 1mJ, and the ignition energy required to evaluate the minimum ignition energy of these samples is extremely low.

[0003] According to the traditional capacitor storage energy calculation formula The size of the ignition energy is determined by the energy storage capacitor C and the charging voltage U. Due to the limitation of the breakdown voltage, the generation of low electrostatic spark energy requires the energy storage capacitor to be as small as possible. However, the existence of parasitic capacitance between lines is difficult to avoid, especially the energy storage capacitor required for the generation of low electrostatic spark energy is at the same order of magnitude as the parasitic capacitance. The extra energy brought by the parasitic capacitance causes a large deviation in the electrostatic spark energy below 1mJ.

[0004] In order to obtain a more accurate spark energy value, the commonly used method is to use a high-voltage probe and a current probe to directly measure the voltage waveform and current waveform at both ends of the discharge electrode, and integrate the formula E = ∫UIdt to obtain the spark energy value. However, in the measurement of low electrostatic spark energy, using a voltage probe to directly measure the spark gap will cause the spark charge to flow into the ground terminal of the measurement circuit, making it difficult to generate electrostatic sparks, and the phase error between the current signal and the voltage signal is difficult to avoid, which seriously affects the accuracy of the integration result. Therefore, this method is not suitable for the measurement of low electrostatic spark energy. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method for generating and measuring low electrostatic spark energy, aiming to generate low electrostatic spark energy while improving measurement accuracy and enhancing test efficiency, thereby providing support for minimum ignition energy testing of sensitive gases and dust clouds.

[0006] In order to achieve the above-mentioned object, the present invention takes into account the influence of parasitic capacitance when calculating the discharge energy, uses the current waveform to calculate the voltage waveform, and replaces the voltage probe measurement to provide a non-contact and phase-error-free low electrostatic spark energy generation and measurement method, comprising the following steps:

[0007] S1. Under a given charging voltage condition, test and obtain the corresponding discharge voltage of different energy storage capacitors;

[0008] S2. Calculate the parasitic capacitance of the front and rear stages of the circuit according to the change of charging and discharging voltage;

[0009] S3, select different charging voltages and energy storage capacitors to perform spark discharge, and test and obtain the current waveform of the spark generating circuit;

[0010] S4. Calculate the discharge terminal voltage waveform according to the current waveform and the parasitic capacitance;

[0011] S5. Calculate the total discharge energy, calculate the resistance offset energy, and subtract the two to obtain the spark energy;

[0012] S6. Fit and establish the relationship between spark energy and charging voltage.

[0013] The generation of low electrostatic spark energy requires that the energy storage capacitor is as small as possible. However, the smaller the energy storage capacitor, the greater the influence of parasitic capacitance on the electrostatic spark energy. At the same time, the energy loss caused by contact measurement cannot be ignored. According to the different influences, the present invention divides the line parasitic capacitance into front and rear stages for measurement; uses small capacitor charging and discharging to generate spark energy, and reduces the spark energy through the voltage divider effect of series resistance, thereby reducing the influence of parasitic capacitance; uses the discharge current waveform to calculate the voltage waveform, which replaces the voltage probe measurement, avoiding the spark energy loss caused by the probe contact and the phase error between the current waveform and the voltage waveform. Finally, the relationship between the spark energy and the charging voltage is established by fitting, thereby improving the test efficiency and providing support for the minimum ignition energy test of sensitive flammable gases and dust clouds. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 4 is a flow chart of low static spark energy generation and measurement according to an embodiment of the present invention.

[0015] Figure 2 FIG. 4 is a schematic diagram of a parasitic capacitance measurement circuit according to an embodiment of the present invention.

[0016] Figure 3 Schematic diagram of a spark energy generating circuit according to an embodiment of the present invention.

[0017] Figure 4 1 is a curve diagram showing the relationship between spark energy and charging voltage according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention relates to a method for generating and measuring low static spark energy, which is mainly used for instruments and equipment that require low static spark energy generation function, such as gas, steam, and dust cloud minimum ignition energy testers. It can improve the accuracy of low static spark energy measurement and enhance the test efficiency, and provide support for the minimum ignition energy test of sensitive gases and dust clouds.

[0019] like Figure 1 As shown, the present invention specifically comprises the following steps:

[0020] S1. Under a given charging voltage condition, test and obtain the corresponding discharge voltage of different energy storage capacitors;

[0021] S2. Calculate the parasitic capacitance of the front and rear stages of the circuit according to the change of charging and discharging voltage;

[0022] S3, select different charging voltages and energy storage capacitors to perform spark discharge, and test and obtain the current waveform of the spark generating circuit;

[0023] S4. Calculate the discharge terminal voltage waveform according to the current waveform and the parasitic capacitance;

[0024] S5. Use E = ∫UIdt to calculate the total discharge energy, and use E = ∫I 2 Rdt calculates the resistance offset energy, and the spark energy is obtained by subtracting the two;

[0025] S6. Fit the relationship curve between spark energy and charging voltage.

[0026] In the above step S1, the parasitic capacitance measurement circuit is as follows: Figure 2 As shown, at the charging voltage U O Under certain conditions, select different capacitance storage capacitors C i Perform charge and discharge test and use high voltage probe to measure the corresponding discharge terminal voltage U Pi , where U O It must meet the requirement of being able to break through the air under given electrode gap conditions; due to the limitation of breakdown voltage, the generation of low electrostatic spark energy requires energy storage capacitor C i As small as possible; R C It is the charging resistor, and its size determines the length of the charging time.

[0027] Wherein, preferably, when the electrode gap is 1 mm, the charging voltage U O Not less than 5kV; energy storage capacitor C i Usually pF level, to meet the capacitor withstand voltage requirements, two capacitors with the same capacitance are connected in parallel, the capacitance includes but is not limited to: 2.5pF, 5pF, 11pF, 23.5pF and 110pF; R C The resistance is 10MΩ.

[0028] The above step S2 is characterized in that the multiple groups of energy storage capacitors C selected by S1 i And its corresponding discharge voltage U Pi , using the formula Q = U O (C i +C P1 )=U Pi (C i +C P1 +C P2 +Cr ), calculate the line front stage parasitic capacitance C P1 and the subsequent parasitic capacitance C P2 Where C r The voltage probe is the capacitance of the voltage probe itself, which is about 3pF. In the measurement of low electrostatic spark energy, using a voltage probe to directly measure the spark gap will cause the spark charge to flow into the ground terminal of the measurement circuit, making it difficult to generate electrostatic sparks. Therefore, the voltage probe is only used for parasitic capacitance measurement and is not used in spark generation circuits.

[0029] In the above step S3, the spark energy generation and measurement circuit is as follows Figure 3 As shown, the charging voltage U is selected to be equal and sufficient to break through the air. O For the energy storage capacitor C i Charge and discharge to generate static sparks, and use a non-contact current probe to measure the current waveform I(t) of the spark generation circuit. M Used to offset the previous stage parasitic capacitance C to a certain extent P1 In low-energy spark discharge, the energy loss caused by the series resistance cannot be ignored. Before the electrode gap breaks down, the gap resistance is much larger than the series resistance. At this time, the gap voltage is close to the discharge end voltage, ensuring that the breakdown voltage meets the requirements. During the breakdown, the gap resistance drops sharply, and the voltage divider effect of the series resistance consumes part of the energy.

[0030] Wherein, preferably, the charging voltage U O The range is 5-9kV, with an interval of 1kV; the energy storage capacitor C i It can be consistent with the capacitance value selected in step S1; R M The resistance is about 1kΩ.

[0031] The above step S4 is characterized by comprising the following steps:

[0032] S4-1. Calculate the capacitor C r Discharge voltage U under the influence P ,

[0033] S4-2. Calculate the charge Q released over time d (t), Q d (t) = ∫I(t)dt;

[0034] S4-3. Calculate the total capacitance C, C = C i +C P1 +C P2 ;

[0035] S4-4. Calculate the function U of the voltage across the total capacitor C as it changes with time C (t),

[0036] The above step S5 is characterized by comprising the following steps:

[0037] S5-1. Calculate the total discharge energy E, E = ∫U C (t)I(t)dt;

[0038] S5-2. Calculate the resistance offset energy E R , E R =∫(R M +R L )I(t) 2 dt, where R L It is the equivalent resistance of the line and can be measured by short-circuiting the electrode gap;

[0039] S5-3. Calculate the spark energy E S , E S =EE R .

[0040] The above step S6 is characterized by fitting to establish the spark energy E S With charging voltage U O By selecting the charging voltage to adjust the spark energy value, the test efficiency can be improved. The fitting method includes but is not limited to: using the power function model E S =aU O b Perform fitting, a and b are fitting coefficients.

[0041] Among them, preferably, Figure 4 The spark energy and charging voltage fitting curve shown, the horizontal axis represents the selected charging voltage U O The vertical axis represents the spark energy E calculated from steps S1 to S5. S , different curves correspond to different selected energy storage capacitors C i With series resistor R M , the fitting degree of each curve (R 2 ) are all above 0.99, and the fitting effect is good.

[0042] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring low static spark energy, characterized in that The following steps are involved: S1. Under a given charging voltage condition, test and obtain the discharge voltage corresponding to different energy storage capacitors; S2. Calculate the parasitic capacitance of the front and rear stages of the circuit according to the change of charging and discharging voltage; S3, select different charging voltages and energy storage capacitors to perform spark discharge, and test and obtain the current waveform of the spark generating circuit; S4. Calculate the discharge terminal voltage waveform according to the current waveform and the parasitic capacitance; S5, calculating the total discharge energy and the resistance offset energy, subtracting the two to obtain the spark energy; S6, fitting and establishing the relationship between spark energy and charging voltage; In step S2, the multiple groups of energy storage capacitors C selected in step S1 are i And its corresponding discharge voltage U Pi , using the formula Q = U O (C i +C P1 )=U Pi (C i +C P1 +C P2 +C r ), calculate the line front stage parasitic capacitance C P1 and the subsequent parasitic capacitance C P2 , where C r is the capacitance of the voltage probe itself; In step S3, a charging voltage U is selected that is equally spaced and sufficient to break through the air. O For the energy storage capacitor C i Performing charging and discharging to generate static sparks; The current waveform I(t) of the spark generating circuit is measured using a non-contact current probe. The series resistance R of the electrode ground terminal is M Used to offset the previous stage parasitic capacitance C P1 The extra spark of energy it brings; Step S4 includes the following steps: S4-1. Calculate the capacitor C r Discharge voltage U under the influence P , S4-2. Calculate the charge Q released over time d (t), Q d (t) = ∫I(t)dt; I(t) is the current waveform of the spark generating circuit; S4-3. Calculate the total capacitance C, C = C i +C P1 +C P2 ; S4-4. Calculate the function U of the voltage across the capacitor C as it changes with time C (t), Step S5 includes the following steps: S5-1. Calculate the total discharge energy E, E = ∫U C (t)I(t)dt; S5-2. Calculate the resistance offset energy E R , E R =∫(R M +R L )I(t) 2 dt, where R L is the equivalent resistance of the line, measured by short-circuiting the electrode gap; R M The resistance in series with the electrode ground terminal; S5-3. Calculate the spark energy E S , E S =EE R .

2. The method according to claim 1, characterized in that In step S1, at the charging voltage U O Under certain conditions, select different capacitance storage capacitors C i Perform charge and discharge test and use high voltage probe to measure the corresponding discharge terminal voltage U Pi .

3. The method according to claim 2, characterized in that The charging voltage U O It must meet the requirement of being able to break through the air under given ignition electrode gap conditions. When the electrode gap is 1mm, the charging voltage U O Not less than 5kV; the energy storage capacitor C i It is in the pF level.

4. The method according to claim 1, characterized in that: In step S6, the power function model E is used S =aU O b Perform fitting, a and b are fitting coefficients.

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