Why can't the multimeter measure the polarity of AC 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 kind of 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, it can be said that it is the simplest method for its instantaneous polarity, then special An electronic instrument oscilloscope used to observe alternating current or direct current pulses.
The direction of alternating current changes at any time, regardless of polarity. If you are talking about measuring the live wire and the neutral wire, you can turn the multimeter to the highest AC voltage, hold the black test lead with one hand, and use the red test lead to detect the wire. In addition, some digital multimeters now have the function of electroscope pen.
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 difference between the diode gear and the on-off gear of the multimeter
The diode block is mainly to measure the forward voltage drop of the diode, and the buzzer file is also called the on-off file, which is mainly to measure the on-off of the line. Some multimeters make the buzzer file and the diode block together, and some multimeters put this The two gears are done separately.
The diode block is mainly a voltage source of about 2.8V generated inside the A/D converter, which is added to the VΩ hole and the COM hole. When you connect the red and black test leads to the two ends of the diode under test, it is mainly the 2.8V voltage source. Measure the forward and reverse conduction voltage drop of the diode.
The on-off gear mainly depends on the operational amplifier to control the sound of the buzzer. If the resistance of the measured circuit is lower than 70 ohms, some are 60 ohms. This resistance depends on the threshold of the operational amplifier. To change the sound resistance of the buzzer, for example, it can be made to ring at 50 ohms.
