Use a multimeter to measure the forward resistance of the diode. Why does each level
The digital multimeter converts the measured resistance value into a digital signal through the A/D conversion chip and then displays the resistance value. The analog multimeter displays the value through the deflection of the magnetic head. If in actual measurement we find that using a digital multimeter There is no resistance in the forward and reverse directions of the diode when tested at the resistance setting, but there is resistance in the forward direction of the diode when tested with a pointer multimeter. This is mainly due to the following reasons:
Diode measurements in circuit boards
First of all, the output voltages of the resistance range of analog multimeters and digital multimeters are different. Generally, the highest voltage output of an analog multimeter is 9 volts, while the highest output voltage of a digital multimeter is generally 3 volts. At the same time, not only are their output voltages different, We choose different gears when measuring, and their output voltages are also different. The output voltage of the resistance gear of a digital multimeter ranges from 1.0 volts to 3.0 volts. The output voltage of the resistance gear of an analog multimeter is generally higher than that of a digital multimeter. The output voltage of an analog multimeter is generally higher than that of a digital multimeter. If the output voltage is greater than the voltage drop value of the diode, the diode can conduct. However, the digital multimeter is sometimes less than the voltage drop value of the diode, causing the diode to fail to conduct. This will cause infinite forward and reverse resistance when measuring the diode.
Secondly, the voltage drop characteristics of the diodes are different, which will also cause the deviation between the results when we choose the resistance setting of the pointer multimeter to measure the diodes and the results of measuring the diodes with a digital multimeter. For example: the general voltage drop value of silicon tubes and germanium tubes is 0.3 Volts to 0.6 volts, but some special diodes, such as high-voltage diodes, have a relatively large conduction voltage drop of more than 0.7 volts. However, the resistance range of our digital multimeter has a low voltage and cannot conduct the diode. Pass, so the resistance will appear infinite when measuring.
When we use a digital multimeter to measure the quality of a diode, it is best to choose the diode gear. The diode gear of the digital multimeter is generally around 2.6 volts, which is generally greater than the forward voltage drop of the diode, and the diode can conduct in the forward direction.
If we want to use the resistance setting to measure whether there is leakage in the diode, we can select the resistance setting of the digital multimeter. At this time, the result should be that there is resistance in the forward measurement, and the resistance in the reverse measurement is infinite. The result of the pointer multimeter measurement is the same. If The measurement found that there is resistance in the reverse direction, which proves that the diode may leak in the reverse direction. In this case, we need to use a special instrument to detect it. It is not accurate to use a multimeter to measure whether the diode has leakage.
