Why can’t a multimeter measure the polarity of alternating current?
The so-called alternating current means 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 is in the unit The number of changes in time is called frequency, and its unit is Hertz, which is a physical unit named in memory of the famous physicist Mr. Hertz. Because the polarity of this power supply changes alternately, it is impossible to measure its polarity with a general multimeter. If it is necessary to know the polarity at a certain moment, which can also be said to be the simplest method of its instantaneous polarity, then specially An oscilloscope is an electronic instrument used to observe alternating current or 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 now have a test pen function.
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, which means that the current changes back and forth 50 times per second and the direction changes 100 times. This problem itself has its own problems.
How to repair the buzzer of an analog multimeter that does not sound
For the commonly used MF47 pointer multimeter, some models have path detection. That is, a buzzer is connected in series in the circuit. Pass buzzer detection; this gear is next to the electrical barrier R*1Ω gear.
This gear is mainly used to quickly judge the on and off status of the circuit. When the measurement is on, the buzzer will immediately beep. You can understand the on/off status of the circuit without looking at the needle indication of the multimeter with your eyes. Condition.
First of all, like the electric barrier, the meter needs to be zeroed. At this time, the buzzer emits a long beep of about 1kHz when working, and the measurement can be carried out. When the resistance value of the circuit being measured is lower than about 10Ω, the buzzer will sound. It should be noted here that the sound size of the buzzer is inversely proportional to the resistance value in the circuit being measured (that is, the greater the resistance value in the circuit, the smaller the sound emitted by the buzzer). At this time, the dial pointer value is approximately R*3 (reference value).
For this kind of pointer multimeter, the damage to the buzzer is mainly caused by the user mistakenly setting the buzzer position to measure the AC voltage. In order to give the questioner a clear way to repair the damaged buzzer.
There are two types of buzzers, one is a piezoelectric ceramic buzzer and the other is an electromagnetic buzzer. Different multimeters use different buzzers. The piezoelectric ceramic buzzer is measured with a multimeter. It has a sound, but the resistance value is very large. The electromagnetic buzzer has a certain resistance value. When it is measured with a multimeter, it will make a buzzing sound.\
