Why can't I measure the polarity of alternating current with a multimeter?
Alternating current is a current that changes periodically in size and direction. It has 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 is problematic.
The so-called alternating current means that the polarity changes alternately, and the change speed is very fast. Whether it is an analog or digital multimeter, it cannot reflect the instantaneous polarity. Its polarity is the number of times it changes per unit time. The unit of frequency is Hertz, which is a unit of physics named in memory of the physicist Mr. Hertz.
The polarity of this kind of 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, which is the simplest method of its instantaneous polarity, it needs to be specially used to observe the alternating current. Or electronic instrument oscilloscope for direct current pulses.
The direction of alternating current changes at any time, regardless of polarity. If you want to test the live wire and neutral wire, you can set the multimeter to the highest AC voltage setting, hold the black test lead with one hand, and use the red test lead to detect the wire. The pointer that deflects is the live wire, and the point that does not deflect is the neutral wire. In addition, some digital multimeters are equipped with a test pen function, which can be used for some common measurement tasks.
How to measure the polarity of electrolytic capacitors with a multimeter?
When a 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. You can use a multimeter to detect the positive and negative poles of the polarized capacitor.
Detection method: Use the resistance setting of a multimeter to measure the forward and reverse resistance of the capacitor. The larger resistance is forward and the smaller resistance is reverse.
Precautions:
(1) Before measurement, use a resistor or wire to discharge the remaining electricity on the capacitor;
(2) The capacitor is charged during measurement. There is a process of charging the capacitor. Wait until the display is basically stable before reading, the result will be more accurate;
(3) The black pen of the analog multimeter is the positive pole and the red pen is the negative pole, while the digital multimeter is just the opposite.
