Multimeter - add low impedance voltage test function
Tip 1: Add low impedance voltage test function
Voltage measurement is the main function of the multimeter. When measuring voltage, the multimeter and the device under test are in a parallel circuit state. In theory, the greater the internal resistance of the multimeter, the smaller the impact on the device under test, and the more accurate the measured voltage value. However, due to the high internal resistance of digital multimeters, most of them can reach more than 1MΩ, which is prone to false readings caused by phantom voltage (induced voltage). In addition, for some special tests, such as testing an open-circuit battery or a small power supply voltage, if the multimeter still maintains a high internal resistance state, it cannot reflect the internal resistance of the power supply 1 battery.
For example, if an aging Ni-MH rechargeable battery is measured with a digital multimeter, there is still more than 1.2V, and the tester judges that the battery is "charged" or "normal". However, when the battery is connected to an electrical appliance with a larger power consumption, the voltage drops rapidly below 1V, and the electrical appliance cannot work normally, indicating that the rechargeable battery is aging and the internal resistance increases significantly. If the battery/power supply is tested with a certain load during the test, the problem of high internal resistance of the battery 1 power supply and "no current discharge" can be found in time. Now some mid-to-high-end multimeters have added a low-impedance voltage test function, the principle of which is to measure with a load. Ordinary multimeter users can make a load by themselves and connect it in parallel to the multimeter when using it. It is generally used to measure batteries. It is recommended to use 200~10000Ω/5W. It is recommended to choose a resistance of 2000~4700Ω/1W or more. Both ends are extended with wires, and alligator clips are installed at the ends of the wires to facilitate clamping on the multimeter pen. The connection between the resistor and the wire should be insulated, such as using a heat shrinkable sleeve or wrapping an insulating tape. In actual use, attention should be paid to the power consumption of the resistor, the online test time should not be too long, and the surface temperature of the resistor should not be too high. In addition, it should be noted that the functions of low-impedance voltage test and load measurement can only be used in special cases, and it is not necessary to use them in routine circuit testing.
