A multimeter cannot measure the polarity of alternating current
Why can't a multimeter measure the polarity of AC power?
AC power is a current that periodically changes in size and direction, without polarity, only with frequency. The frequency of AC power in China is 50 Hz, which means that the current changes back and forth 50 times per second and changes direction 100 times. This problem itself is problematic.
The so-called alternating current refers to the alternating changes in polarity, 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 in unit time, called frequency, and the unit is Hertz. This is a physical unit named in memory of physicist Mr. Hertz.
The alternating polarity of this power supply cannot be measured with a general multimeter. If it is necessary to understand the polarity at a certain moment, which is the simplest method for its instantaneous polarity, electronic instrument oscilloscopes dedicated to observing AC or DC pulses are needed.
The direction of alternating current changes at any time, regardless of polarity. If measuring the zero line of the live wire, you can set the multimeter to the highest level of AC voltage, hold the black pen with one hand, and use the red pen to detect the wire. The pointer that deflects is the live wire, and the pointer that does not deflect is the zero line. In addition, some digital multimeters have a verification pen function that can be used for some commonly used measurement work.
How to measure the polarity of Electrolytic capacitor with a multimeter?
When a polar capacitor is connected in the forward direction, the leakage is small, and when connected in the reverse direction, the leakage is large. A multimeter can be used to detect the positive and negative poles of the polar capacitor.
Detection method: Use a multimeter to measure the positive and negative resistance of the capacitor, with high resistance indicating positive direction and low resistance indicating negative direction.
Precautions:
(1) Before measuring, discharge any remaining electricity on the capacitor using a resistor or wire;
(2) When measuring, the capacitor is charged, and there is a process of charging the capacitor. When the display is basically stable, the reading will be more accurate;
(3) The black pen of a pointer type multimeter is the positive pole, while the red pen is the negative pole, while a digital multimeter is the opposite.
