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Hello everyone, in this lesson we will talk about the measurement and judgment of diodes

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When measuring diodes, you need to use the diode file of the multimeter

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For example, as shown in the figure below,

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when the multimeter is adjusted to the diode range, a diode symbol will be displayed on the screen

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When the multimeter is adjusted to the diode position,

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the red marker is positively charged, and the black marker is negatively charged

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Use the red marker and the black marker to touch the two ends of the diode respectively

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When the red marker is connected to the positive pole and the black marker is connected to the negative pole,

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it is positive measurement

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The value will be displayed on the screen, the silicon tube should be 300-800,

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the germanium tube should be 100-300

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When the red marker is connected to the negative pole and the black marker is connected to the positive pole,

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it is reverse measurement at this time

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The value displayed on the screen should be OL

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As shown in the figure below, this is the reverse measurement of the diode

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The measured value is OL

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Next, let's measure it in real

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First turn the multimeter to the diode file

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At this time, a diode symbol will be displayed on the screen.

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Next we measure the two diodes

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The red marker is connected to the positive pole of the diode,

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and the black marker is connected to the negative pole of the diode.

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At this time, it is positive measurement

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The measured value is 625

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Explain that this is a silicon tube

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Use the same method to measure the following diode

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The measured value is 113

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Explain that this diode is a germanium diode

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Next we swap the pens

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Reverse measurement of these two diodes

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It can be seen that the measured values are all OL

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After understanding the measurement method of the diode,

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we will use this measurement method to judge whether the diode is good or bad.

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After the diode is damaged, its manifestations generally have two forms:

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One is conduction without reaching the conduction condition

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The other is to reach the conduction condition and not conduction

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According to the form of the diode after it is damaged,

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we can get the measurement method for judging whether the diode is good or bad.

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When measuring in the forward direction, if the measured value is not 100-800,

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it means that the diode is damaged

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When measuring in reverse, the measured value is not OL,

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which also indicates that the diode is damaged

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Here we need to pay attention that this method is an offline measurement method,

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that is, the diode needs to be removed for measurement

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If we measure online, the reverse measurement will generally not be OL

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The reverse measurement will also have a value,

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but its value must be much greater than the forward measurement

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Next, let's judge in reality

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This is a computer mainboard

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We find a diode

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You can see that there is a diode here, let's measure it

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The red marker is connected to the positive pole of the diode,

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and the black marker is connected to the negative pole of the diode.

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It can be seen that the measured value is 246

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Reverse measurement of the marker, the measured value is 1874,

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which is far greater than the value of the forward measurement

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Indicates that this diode is a good diode