Method for measuring large capacitance based on anti-interference small signal

Abstract

The application discloses a method for measuring a large capacitance based on an anti-interference small signal, and the method is characterized in that: data acquisition and analysis are performed on charge-discharge waveforms, 50Hz or 60Hz space interference is combined with a small signal, and the interference signal is algorithmically inhibited according to the characteristics of the interference signal, so that the measurement precision of the small signal can be ensured in the presence of the interference signal; the method uses a small signal to measure a large capacitance without increasing the power consumption of a constant current source, and the measurement precision of the method is ensured by using a multimeter to measure the large capacitance; the speed is obviously improved, the slope can be calculated in real time during charging and discharging, the capacitance value can be directly estimated according to the charging and discharging slope, the gear is quickly locked, and the method does not need to wait for a certain period of time after charging and then perform judgment, so that the speed of automatic gear shifting of the large capacitance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of instrument technology, and in particular to a method for measuring large capacitance based on anti-interference small signal. BACKGROUND

[0002] In the large capacitance measurement function of a multimeter, the charging and discharging of the test large capacitance is limited by the cross current, the charging or discharging time principle is obtained, and the measured capacitance is calculated according to the change of the voltage corresponding to the charging and discharging time under the cross current mode. Due to the limitation of the constant current source of the multimeter, the larger the capacitance is, the longer the time of charging to the set voltage is. Assuming that the charging voltage is reduced to shorten the charging time, but because the signal is small, the influence of the mains on the small signal is large, which directly affects the measurement accuracy. The current measurement scheme has two problems: ensuring accuracy but taking too long to test; reducing the measurement time is difficult to meet the product design accuracy. SUMMARY

[0003] The purpose of the present application is to provide a method for measuring large capacitance based on anti-interference small signal.

[0004] The technical solution adopted by the present application is:

[0005] A method for measuring large capacitance based on anti-interference small signal, the system adopted includes a voltage-limited automatic charging and discharging control unit, a data storage unit, a data analysis unit, a measured capacitance, and a constant current source unit, a fast discharging unit, and an ADC signal acquisition unit connected to the measured capacitance; an external capacitance line as an interference signal is connected to the measured capacitance and the AD signal acquisition unit; the ADC signal acquisition unit is connected to the data storage unit, the data analysis unit and the voltage-limited automatic charging and discharging control unit; the voltage-limited automatic charging and discharging control unit is connected to and controls the constant current source unit and the fast discharging unit; the method includes the following steps:

[0006] Step 1, the system determines whether the measured capacitance is connected to the measurement system; if yes, step 2 is executed; otherwise, step 1 is executed;

[0007] Step 2, the constant current source unit starts charging the measured capacitance, and the AD signal acquisition unit collects the charging waveform;

[0008] Step 3, when the charging waveform collection is completed or it is determined whether the charging threshold is reached, the fast discharging of the measured capacitance is started, and the number of ADC acquisitions for signal suppression and anti-interference is calculated based on the collected waveform data and the capacitance value of the measured capacitance is calculated;

[0009] Step 4, configure the ADC signal acquisition unit according to the number of ADC acquisitions of the signal suppression anti-interference, and judge whether the measurement gear needs to be changed based on the capacitance value of the measured capacitor; if yes, change the gear to the corresponding measurement gear according to the capacitance value and execute step 2; otherwise, execute step 2.

[0010] Further, in step 3, judge whether the discharge of the measured capacitor reaches the discharge threshold during the rapid discharge process of the measured capacitor; if yes, stop discharging and wait for recharging; otherwise, continue discharging the measured capacitor.

[0011] Further, the suppression step of the interference signal in step 3 is as follows:

[0012] Step 3-1, calculate the signal period of 50Hz and 60Hz power supply respectively;

[0013] Specifically, the signal period t1 of 50Hz power supply is 1 / 50=20ms; the signal period t1 of 60Hz power supply is 1 / 60=16.666ms.

[0014] Step 3-2, obtain the least common multiple t3 of the signal periods of 50Hz and 60Hz power supply; t3=100ms;

[0015] Step 3-3, calculate the integer period of 50Hz and 60Hz power supply signals based on the least common multiple respectively;

[0016] Specifically, the integer period of 50Hz power supply signal t3 / t1=100 / 20=5; the integer period of 60Hz power supply signal t3 / t2=100 / 16.666=6;

[0017] Step 3-4, calculate the number Pn of ADC acquisitions under the least common multiple based on the waveform sampling rate fs;

[0018] Step 3-5, calculate the charging voltage change rate;

[0019]

[0020] Wherein, Vstep represents the voltage change rate calculated for each interval; i represents the acquisition voltage coordinate value; n represents the number of calculated acquisition voltage values; adc_vol represents the current coordinate voltage value;

[0021] Step 3-6, calculate the capacitance value of the measured capacitor based on the charging voltage change rate, and the calculation formula is as follows:

[0022] C=I*fs / Vstep

[0023] Wherein, C represents the capacitance value of the measured capacitor; I represents the charging constant current source current.

[0024] The application adopts the above technical scheme, and proposes to use signals and systems as a theoretical basis to collect and analyze data of charge-discharge waveforms without modifying hardware and increasing costs, to combine spatial interference of small signal 50Hz or 60Hz, to suppress interference signals according to characteristics of the interference signals, and to ensure measurement accuracy of the small signal in the presence of the interference signals. Since the application uses small signal measurement without increasing power consumption of the constant current source, the measurement speed of the multimeter for measuring large capacitors is obviously improved, and the slope can be calculated in real time during charging and discharging, the capacitance value can be directly estimated according to the charge-discharge slope, the gear is quickly locked, and it is not necessary to wait for a certain period of time for charging and then to judge, so that the speed of automatic gear shifting of the large capacitor is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0026] Fig. 1 A flowchart of the application of a method for quickly measuring a large capacitor based on an anti-interference small signal is shown.

[0027] Fig. 2 A frame structure diagram of a test system of the application is shown.

[0028] Fig. 3 A charge-discharge waveform diagram of a measured capacitor is shown. EMBODIMENT

[0029] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme of the embodiments of the application will be described clearly and completely in combination with the drawings of the embodiments of the application.

[0030] The core of the application is to collect charge-discharge waveforms of a measured capacitor, to combine signal systems for signal suppression and anti-interference processing, so as to ensure measurement accuracy and speed up the measurement speed. The system used for measurement of the application includes a constant current source unit, a voltage limiting automatic control charge-discharge unit, an AD signal collection unit, a data storage unit and a data analysis unit.

[0031] As Figs. 1 to 3The application discloses a method for measuring a large capacitor based on anti-interference small signal, and the method comprises the following steps: a voltage-limited automatic charging and discharging control unit, a data storage unit, a data analysis unit, a measured capacitor, a constant current source unit, a fast discharging unit and an ADC signal acquisition unit are adopted; an external capacitor line is connected to the measured capacitor and the ADC signal acquisition unit as an interference signal; the ADC signal acquisition unit is connected to the data storage unit, the data analysis unit and the voltage-limited automatic charging and discharging control unit; the voltage-limited automatic charging and discharging control unit is connected to and controls the constant current source unit and the fast discharging unit; and the method comprises the following steps:

[0032] Step 1: the system judges whether the measured capacitor is connected to the measurement system; if yes, step 2 is performed; otherwise, step 1 is performed.

[0033] Step 2: the constant current source unit starts charging the measured capacitor, and the ADC signal acquisition unit collects the charging waveform;

[0034] Step 3: when the charging waveform collection is completed or it is judged that the charging threshold is reached, the fast discharging of the measured capacitor is started, and the number of ADC acquisitions for signal suppression and anti-interference is calculated based on the collected waveform data, and the capacitor value of the measured capacitor is calculated.

[0035] Step 4: the ADC signal acquisition unit is configured according to the number of ADC acquisitions for signal suppression and anti-interference, and it is judged whether the measurement gear needs to be changed based on the capacitor value of the measured capacitor; if yes, the measurement gear is changed to the corresponding measurement gear according to the capacitor value, and step 2 is performed; otherwise, step 2 is performed.

[0036] Further, in step 3, it is judged whether the discharging of the measured capacitor reaches the discharging threshold during the fast discharging process; if yes, the discharging is stopped and the charging is waited again; otherwise, the discharging of the measured capacitor is continued.

[0037] Further, the interference signal suppression step in step 3 is as follows:

[0038] Step 3-1: the signal periods of 50Hz and 60Hz power supply are calculated respectively;

[0039] Specifically, the signal period t1 of 50Hz power supply is 1 / 50=20ms, and the signal period t1 of 60Hz power supply is 1 / 60=16.666ms.

[0040] Step 3-2: the least common multiple t3 of the signal periods of 50Hz and 60Hz power supply is obtained; t3=100ms;

[0041] Step 3-3: the integer periods of 50Hz and 60Hz power supply signals are calculated based on the least common multiple respectively;

[0042] Specifically, the integer period of the 50Hz mains signal t3 / t1=100 / 20=5; the integer period of the 60Hz mains signal t3 / t2=100 / 16.666=6;

[0043] Step 3-4, based on the waveform sampling rate fs, the number of ADC acquisitions Pn for calculating the least common multiple is calculated;

[0044] Step 3-5, the charging voltage change rate is calculated;

[0045]

[0046] Wherein, Vstep represents the calculation of each interval voltage change rate; i represents the acquisition voltage coordinate value; n represents the number of acquisition voltage values; adc_vol represents the current coordinate voltage value;

[0047] Step 3-6, based on the charging voltage change rate, the capacitance value of the measured capacitor is calculated, and the calculation formula is as follows:

[0048] C=I*fs / Vstep

[0049] Wherein, C represents the capacitance value of the measured capacitor; I represents the charging constant current source current.

[0050] Specific working principle: when the device is used, there will be 50Hz or 60Hz mains interference signal, which needs to consider the simultaneous suppression of 50Hz and 60Hz signals, at this time, 2 signals need to be satisfied at the same time. When the signal length is 100mS, 50Hz is 5 complete periods, and 60Hz signal is 6 complete periods. The interference signal is an integer period, so as long as the average value is calculated, all interference signals can be easily eliminated, only the measured capacitor charging and discharging voltage change value is left, so that the change of the capacitor charging voltage can be accurately calculated in the case of small signal interference, and the capacitance value can be accurately measured. In the process of capacitor charging and discharging, the collected data can be operated, and the measured capacitance value can be calculated in real time, so that the measurement gear can be quickly determined, and the measurement gear can be adjusted in time, so as to prevent the capacitor from being charged with a large amount of energy, resulting in a long waiting time for discharging in subsequent gear shifting. This also solves the problem of slow automatic gear shifting experience in large capacitor measurement. From the perspective of production, large capacitor calibration and verification accounts for a large proportion of the entire production, which directly leads to the decline of production efficiency. The use of voltage change and time operation in this scheme only needs to calibrate the voltage and time of one gear, and the calibration gear coefficient can be directly used to other gears, thereby reducing the number of calibration gears and test gears, and prompting the production efficiency of the equipment.

[0051] The application uses the above technical scheme, under the premise of not modifying hardware and increasing cost, proposes to use signal and system as a theoretical basis to collect and analyze data of charge-discharge waveform, combines 50Hz or 60Hz space interference caused by small signal interference, and suppresses the interference signal by algorithm according to the characteristics of the interference signal, so as to ensure the measurement accuracy of the small signal in the presence of the interference signal; since the application uses the small signal measurement under the condition of not increasing the power consumption constant current source, the measurement speed is obviously improved under the condition of ensuring the measurement accuracy of the multimeter measuring large capacitance, and the slope can be calculated in real time during charging and discharging, the capacitance value can be directly estimated according to the charging and discharging slope, the gear is quickly locked, and it is not necessary to wait for a certain period of time after charging and then judge, so as to improve the speed of automatic gear shifting of large capacitance.

[0052] Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

Claims

1. A method for fast measurement of a large capacitance based on an anti-interference small signal, characterized in that: The system comprises a voltage-limited automatic charge-discharge control unit, a data storage unit, a data analysis unit, a measured capacitor, a constant current source unit connected to the measured capacitor, a fast discharge unit, an ADC signal acquisition unit; an external capacitor line as an interference signal is connected to the measured capacitor and the AD signal acquisition unit respectively; the ADC signal acquisition unit is connected to the data storage unit, the data analysis unit and the voltage-limited automatic charge-discharge control unit respectively; the voltage-limited automatic charge-discharge control unit is connected to and controls the constant current source unit and the fast discharge unit; the method comprises the following steps: Step 1: the system judges whether the measured capacitor is connected to the measurement system; if yes, step 2 is executed; otherwise, step 1 is executed; Step 2: the constant current source unit starts charging the measured capacitor, and the AD signal acquisition unit collects the charging waveform; Step 3: when the charging waveform collection is completed or it is judged that the charging threshold is reached, the fast discharge of the measured capacitor is started, and the number of ADC acquisitions for signal suppression and anti-interference is calculated based on the collected waveform data, and the capacitance value of the measured capacitor is calculated; In step 3, the specific steps of calculating the number of ADC acquisitions for signal suppression and anti-interference and calculating the capacitance value of the measured capacitor are as follows: Step 3-1: the signal periods of 50Hz and 60Hz power are calculated respectively; Step 3-2: the least common multiple t3 of the signal periods of 50Hz and 60Hz power is obtained; Step 3-3: the integer periods of 50Hz and 60Hz power signals are calculated based on the least common multiple respectively; Step 3-4: the number of ADC acquisitions Pn under the least common multiple is calculated based on the waveform sampling rate fs, Pn = fs / (1 / t3); Step 3-5: the charging voltage change rate is calculated; Wherein, Vstep represents the voltage change rate calculated for each interval; i represents the collected voltage coordinate value; n represents the number of calculated voltage values; adc_vol represents the current coordinate voltage value; Step 3-6: the capacitance value of the measured capacitor is calculated based on the charging voltage change rate, and the calculation formula is as follows: C = I*fs / Vstep Wherein, C represents the capacitance value of the measured capacitor; I represents the charging constant current source current; Step 4: the ADC signal acquisition unit is configured according to the number of ADC acquisitions for signal suppression and anti-interference, and it is judged whether the measurement gear needs to be changed based on the capacitance value of the measured capacitor; if yes, the measurement gear is shifted to the corresponding measurement gear according to the capacitance value and step 2 is executed; Otherwise, step 2 is executed.

2. The method of claim 1, wherein: In step 3, it is judged whether the discharge of the measured capacitor reaches the discharge threshold during the fast discharge process of the measured capacitor; if yes, the discharge is stopped and the charging is waited again; otherwise, the measured capacitor continues to discharge.

3. The method of claim 1, wherein: In step 3-2, the least common multiple t3 = 100ms.

4. The method of claim 3, wherein: The waveform sampling rate fs=1.2kSPS in step 3-4, then calculate the number of ADC acquisition data for calculating

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