Use a multimeter to measure the forward resistance of the diode, why each gear?
Digital multimeter converts the measured resistance value into a digital signal through A/D conversion chip, and then displays the resistance value. Pointer multimeter displays the numerical value by deflection of the magnetic head. If we find that there is no resistance value in both the forward and reverse directions when using digital multimeter to test the diode resistance, there are the following reasons:
Diode measurement in circuit board
First of all, the output voltage of pointer multimeter is different from that of digital multimeter. Generally, the highest output voltage of pointer multimeter is 9 volts, while that of digital multimeter is 3 volts. At the same time, not only are their output voltages different, but we choose different gears when measuring, and their output voltages are also different. The output voltage of digital multimeter resistance file ranges from 1.0 volts to 3.0 volts. The resistance output voltage of pointer multimeter is generally higher than that of digital multimeter. The output voltage of pointer multimeter is greater than the voltage drop value of diode, and diode can be turned on. However, digital multimeter is sometimes less than the voltage drop value of diode, which will cause infinite forward and reverse resistance when measuring diode.
Secondly, the diode's voltage drop characteristics are different, which will also lead to the deviation between the diode measured by pointer multimeter and the diode measured by digital multimeter. For example, the voltage drop of silicon tube and germanium tube is generally between 0.3 V and 0.6 V, but some special diodes, such as high-voltage diodes, have a relatively large on-off voltage drop, which is generally above 0.7 V. However, our digital multimeter has a low resistance file voltage and cannot turn on the diode, so the resistance will be caused during measurement.
When we use digital multimeter to measure the quality of diode, it is best to choose the diode gear. The diode gear of digital multimeter is generally about 2.6 volts, which is generally greater than the forward voltage drop of diode, and the diode can be turned on in the forward direction.
If we want to use the resistance file to measure whether there is leakage in the diode, we can choose the resistance file of the digital multimeter. At this time, the result should be that there is resistance in the forward direction and infinite resistance in the reverse direction. The result measured by the pointer multimeter is the same. If there is resistance in the reverse direction, it proves that there may be leakage in the reverse direction of the diode. In this case, we need to use a special instrument to detect it. It is not accurate to use a multimeter to measure whether there is leakage in this diode.
