Communication room and other industries. If the battery failure or lack of capacity, it is possible to cause a major accident, it is necessary to conduct a comprehensive online monitoring of the operating parameters of the special battery. One of the important signs of resistance method is its battery condition. Whether it is the battery failure coming, insufficient capacity or improper charge discharge, can be reflected from the change of the battery's internal resistance. Therefore, by measuring the internal resistance of the battery can be extraordinary to assess the status of their work. The method of measuring the internal resistance of battery has the following special:
(1) density method
Density method mainly through the measurement of electrolyte density to estimate the battery's internal resistance, internal resistance measurement commonly used in open type lead-acid batteries, not suitable for measuring internal resistance of lead-acid battery. The scope of application of this method is narrow.
(2) open circuit voltage method
The open circuit voltage method is to estimate the resistance of the battery by the battery terminal voltage measurement, the accuracy is poor, even a wrong conclusion. Because even if a battery capacity has become very small, then the floating state of terminal voltage is still likely to be normal.
(3) DC discharge
DC discharge is through instantaneous large current discharge of the battery, the battery on the measurement of instantaneous voltage drop, calculated by the ohm internal resistance of the battery. Although this method has been widely used in practice, but it also has some shortcomings. The internal resistance of the battery must be tested in static or is offline if using this method, can realize online measurement. And large current discharge will cause a great damage to the battery, thereby affecting the capacity and life of the battery.
(4) AC injection method
By the method of AC AC current signal of IS battery into a constant, the measured battery voltage at both ends of the response signal of Vo, and the phase difference from the impedance formula to determine the battery's internal resistance R. This method does not need to discharge the battery, can realize online detection of battery internal resistance and safety, so it will not affect the performance of the battery. But this method requires measurement of AC current and voltage response Is signal, Vo signal, and the phase difference between voltage and current, thus this method is not only more interference factors, but also increases the complexity of the system, but also affect the measurement accuracy. In order to solve the defects of each method, this paper adopts four terminal measurement method, the battery voltage on both ends of the response signal through the communication circuit and differential sine signal generating a constant AC source after the analog multiplier multiply the analog output voltage multiplier signal through the filter circuit, the AC signal into a DC signal, DC signal the DC amplifier analog-to-digital conversion, the converted value into the SCM process.
(5) resistance tester
Internal resistance tester is used to measure the internal impedance of battery and battery acidification film damage degree of the instrument, hereinafter referred to as the instrument. It is applied to 1KHz AC signal of the measured object, and obtain the resistance by measuring the AC voltage drop. (principle, it is different from the multimeter to measure the resistance of the measured value is milliohm level, while the multimeter value is Ohm level; and the multimeter can only measure the object without power resistance, and resistance instrument can measure the object without power resistance, but also can measure the power of object resistance, so they may not be equal) degradation state to determine the size of the internal resistance of the battery using resistance, (generally) the better the performance of the battery resistance is small. Therefore, the method of measuring the internal resistance of battery detection is a good method with fast speed and high reliability.
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