The difference between the diode mode and the on/off mode of a multimeter
The diode mode is mainly used to measure the forward voltage drop of the diode, while the buzzer mode, also known as the on/off mode, is mainly used to measure the continuity of the circuit. Some multimeters combine the buzzer mode with the diode mode, while others separate these two modes.
The diode block mainly generates a voltage source of about 2.8V inside the A/D converter, which is applied to the V Ω hole and COM hole. When you connect the red and black probes to the two ends of the tested diode, it is mainly this 2.8V voltage source to measure the forward and reverse conduction voltage drop of the diode.
The on-off mode mainly relies on the operational amplifier to control the buzzer to sound. If the resistance of the tested circuit is lower than 70 ohms, some are 60 ohms, and this resistance depends on the threshold of the operational amplifier. That is to say, we can change the buzzer's sound resistance value by changing the operational amplifier's sound threshold, for example, we can make it sound at 50 ohms.
Why can't a multimeter measure the polarity of alternating 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.
