Why can't a multimeter measure the polarity of AC current?
The so-called alternating current refers to the fact that its polarity changes alternately, and the speed of change is very fast. Whether it is a pointer type or a more advanced general digital multimeter, it cannot reflect its instantaneous polarity. Its polarity changes the number of times per unit time, which is called frequency. Its unit is Hertz, which is named in honor of the famous physicist Mr. Hertz. Due to the alternating polarity of this power supply, it is impossible to measure its polarity with a general multimeter. If it is necessary to understand the polarity at a certain moment, it can be said that the simplest method for instantaneous polarity is to use an electronic instrument oscilloscope specifically for observing AC or DC pulses.
The direction of alternating current changes at any time, regardless of polarity. If you want to measure the live wire and neutral wire, you can set the multimeter to the highest AC voltage level, hold the black probe with one hand, and use the red probe to detect the wire. If the pointer is deflected, it is the live wire, and if it is not deflected, it is the neutral wire. In addition, some digital multimeters now come with a verification pen function.
AC power is a current that periodically changes in size and direction, without polarity, only frequency. In China, the frequency of AC power is 50 hertz, which means that the current changes back and forth 50 times per second and the direction changes 100 times. This problem itself is problematic.
How to use a digital multimeter
1. Measure the voltage. Firstly, it is necessary to select the appropriate gear based on the type of voltage being measured, including DC voltage gear and AC voltage gear. The red probe is inserted into the V Ω hole, and the black probe is inserted into the COM hole. Connect the multimeter in parallel to both ends of the tested circuit. If measuring DC voltage, select a range larger than the measured voltage, connect the black probe to the negative terminal and the red probe to the positive terminal, and read the value. If measuring AC voltage, select the appropriate range, connect the red and black probes to the live and neutral wires respectively, and read the value.
2. Measure the current. To measure current with a multimeter, it is necessary to connect the multimeter in series with the tested circuit, and it is also divided into DC current and AC current levels. Insert two red probes into the mA or A hole, and insert the black probe
Enter the COM port, select the appropriate range and gear, string the multimeter in the tested circuit, and read the value.
3. Measure the resistance. To measure resistance with a multimeter, connect the red probe to the V Ω hole and the black probe to the COM hole. Choose the appropriate range, connect the red and black probes to both ends of the resistor, and read the value.
4. Measure capacitance. Before measurement, the capacitor needs to be short circuited and discharged, and then the appropriate range should be selected. Insert the red probe into the V Ω hole and the black probe into the COM hole. If there is a polarized capacitor being measured, connect the red probe to the positive pole and the black probe to the negative pole, and read the value. If measuring non-polar capacitance, the red and black probes can be connected in the positive and negative directions to the capacitor.
5. Measure the diode. Select the diode gear, insert the red probe into the V Ω hole and the black probe into the COM hole, connect the red probe to the positive terminal of the diode and the black probe to the negative terminal of the diode, and read the value. This measurement is to measure the voltage drop of the diode, not the resistance value, which is also a common confusion among many friends. Generally, the voltage drop of a silicon rectifier tube is around 0.7, while that of a germanium tube is around 0.2. Of course, it depends on the type of diode, and the voltage drop of the tube varies depending on the type.
