What is the reason why the multimeter cannot measure the polarity of alternating current
Alternating current is a current that changes periodically in size and direction. There is no polarity, only frequency. The frequency of alternating current in my country is 50 Hz, that is, the current changes back and forth 50 times per second, and the direction changes 100 times. This problem itself has problems.
The so-called alternating current means that the polarity changes alternately, and the speed of change is very fast. Whether it is a pointer type or a digital multimeter, it cannot reflect the instantaneous polarity. Its polarity is the number of times it changes within a unit time. The unit of frequency is Hertz, which is a physical unit named in memory of the physicist Mr. Hertz.
The polarity of this power supply changes alternately, and it is impossible to measure its polarity with a general multimeter. If it is necessary to know the polarity at a certain moment, that is, the simplest method for its instantaneous polarity, it needs to be specially used to observe the alternating current. Or an electronic instrumentation oscilloscope for direct current pulses.
The direction of alternating current changes at any time, regardless of polarity. If you want to measure the live wire and the neutral wire, you can turn the multimeter to the highest AC voltage, pinch the black test lead with one hand, and use the red test lead to detect the wire. In addition, some digital multimeters have the function of electroscope pen, which can be used for some common measurement work.
How to use a multimeter to measure the polarity of electrolytic capacitors?
When the polarized capacitor is connected in the forward direction, the leakage is small, and when it is connected in the reverse direction, the leakage is large. A multimeter can be used to detect the positive and negative poles of the polarized capacitor.
Detection method: Use a multimeter to measure the positive and negative resistance of the capacitor. The larger resistance is forward, and the smaller resistance is reverse.
Precautions:
(1) Before measuring, use a resistor or wire to discharge the remaining electricity on the capacitor;
(2) When measuring, the capacitor is charged, and the charging of the capacitor has a process. Wait until the display is basically stable before reading, and the result will be more accurate;
(3) The black pen of the pointer multimeter is the positive pole, and the red pen is the negative pole, while the digital multimeter is just the opposite.
