Multimeter resistance gear to measure the diode forward and reverse resistance does not show values
Why diodes can not be measured with a resistance gear
The unidirectional conductive property of a diode is conditional on the diode's PN junction being forward biased before it conducts. Simply with the resistance gear to measure the resistance, the diode itself does not conduct, so the resistance can not be measured. Multimeter diode gear are with voltage is generally 1.5-2.8V or so, in the measurement of the diode is actually the voltage on both sides of the diode, so that the PN junction forward bias, which is in the multimeter to see a voltage drop of 0.7V or so, proving that the diode is good. The resistance of about 10K measured by the pointer meter is not accurate, and the values obtained by measuring different diodes are different.
Multimeter diode measurement method
You must use the diode gear of the multimeter to measure the diode. Hit the multimeter's gear to the diode gear, insert the red pen into the positive end and the black pen into the negative end.
Contact the two electrodes of the measured diode with the red and black pens, and if the diode shows a voltage drop of about 0.7V, it means that the end contacted by the red pen is the positive pole of the diode, and the other side is the negative pole of the diode.
Switch the direction of the measured diode, if the voltage value is not measured, it indicates that the red meter pen is contacting the negative pole of the diode, and the black meter pen is contacting the positive pole of the diode.
After the above two measurements, you can confirm the diode's positive and negative poles, and can confirm that the diode is good or bad.
Digital multimeter in the resistance file, the voltage between the two pens is low, lower than the ordinary silicon diode 0.6-0.7V or so positive conduction voltage, the diode is in the cut-off state. The resistance value of the cut-off state is very large, so when measuring the diode with a digital multimeter, whether it is forward or reverse, it shows that the value is overflowing. Digital multimeter have diode measurement gear, you should use the gear to measure the diode forward and reverse on and off.
In addition, the diode is a non-linear component. In addition, the diode is a non-linear component, the resistance value is not fixed, when the pointer multimeter resistance file to measure the diode's forward conduction resistance, it can be seen that the difference between the different gear resistance value is very large. Therefore, the measurement of diode resistance value with a multimeter is not significant, as long as the measurement of forward conduction, reverse cutoff, or to identify the positive and negative poles, to identify the breakdown or burnt out on the line, there is no need to read the specific resistance value.
Digital multimeter has a specialized secondary tube file used to measure the diode. If you have to use the resistance file, diode reverse
There are dozens of K or more resistance values, so the table shows overflow 1. Forward a few hundred ohms to a few K, because the semiconductor diode voltage added to the ends of different resistance values are different. So measure the diode is generally measured with a special file, reverse is generally 1 (overflow), forward between 300 - 750 (this is actually the voltage drop), mostly in the six hundred or so (silicon), 500 or less (germanium) tube.
