How to measure the quality and polarity of diodes with a multimeter

1. Measurement quality: When measuring, the multimeter should be set to the r×100 or r×1k block (r×1 or r×10k block cannot be used, the former has too much current, and the latter has too high a battery voltage in the meter. may cause damage to the diode), connect the red (+) and black (-) meter rods to the two poles of the diode respectively, and measure that the forward and reverse resistances are very large, indicating an internal disconnection; the resistance value is zero or very small , it is a short circuit between the two poles. If the measured forward and reverse resistance values ​​are almost equal, this kind of tube is not easy to use.

2. Use a multimeter to determine the polarity of the diode: When using a diode, the polarity should be correct. Generally, there is a red dot positive mark printed on the outside of the tube (there are also a few tubes with a red dot indicating the negative pole). Some have logos printed on the tube shell. If there is no mark, you can use a multimeter to measure the forward and reverse resistance of the diode to judge. Since the multimeter is electrically blocked, the black (-) meter rod is connected to the positive electrode of the battery in the meter, and the red (+) meter rod is connected to the negative electrode of the battery in the meter. Therefore, when a smaller resistance value is measured, the diode and black (-) The electrode connected to the meter rod is the positive electrode, and the other electrode is the negative electrode.