1. Judging the positive and negative electrodes From the appearance, the positive end of the metal-packed steady-state diode tube is planar, and the negative end has a semi-circular shape. One end of the plastically sealed diode body printed with a color mark is a negative electrode, and the other end is a positive electrode. For the Zener diode with unclear mark, the polarity can also be judged by a multimeter. The measurement method is the same as that of the ordinary diode. That is, the multimeter pen is connected to the two electrodes of the Zener diode by the multimeter R×1k file, and one is measured. After the result, the two test leads are measured again. In the two measurement results, the resistance value is smaller, the black meter is connected to the positive pole of the Zener diode, and the red meter is connected to the cathode of the Zener diode.
If the positive and negative resistances of the Zener diode are measured to be small or infinite, the diode is broken or open circuit damaged.
2. The voltage regulation value is measured by 0~30V continuously adjustable DC power supply. For the Zener diode below 13V, the output voltage of the regulated power supply can be adjusted to 15V, and the positive pole of the power supply is connected in series with a 1.5kΩ current limiting resistor. Connect the negative pole of the Zener diode, connect the negative pole of the power supply to the positive pole of the Zener diode, and measure the voltage across the Zener diode with a multimeter. The measured reading is the voltage regulator diode. If the regulation voltage of the Zener diode is higher than 15V, the regulated power supply should be adjusted to 20V or more.
Test power can also be supplied to the Zener diode with a megger below 1000V. The method is: connecting the positive end of the megohmmeter to the negative pole of the Zener diode, and after the negative end of the megohmmeter is connected with the positive pole of the Zener diode, shake the megohmmeter handle at a uniform speed according to the specification, and monitor the voltage regulator with a multimeter. The voltage value across the diode (the voltage of the multimeter should be determined according to the magnitude of the stable voltage). When the indication of the multimeter's indicated voltage is stable, this voltage is the stable voltage of the Zener diode.
If the steady voltage value of the measured Zener diode is high or low, the diode is unstable.
Figure 4-72 shows the measurement method of the Zener diode regulation value. 
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