Pointer multimeter to measure positive and negative diodes
A normal diode, measured with the resistance of the pointer meter, if it is in the state of conduction, is not the black pen contact level for the diode's positive pole, the red pen for the negative pole! With a digital meter, if it is in the on state, the conclusion is the opposite (red pen is positive)! Is that so?
First thing to know:
Measuring a diode with a pointer multimeter yields the forward and reverse resistance of the diode.
Measuring the diode with a digital multimeter yields the diode's on-state voltage drop.
Also know this:
The red and black pens of a pointer multimeter are connected to the negative and positive terminals of the working battery through components in the meter.
The red and black pens of the digital multimeter are connected to the positive and negative terminals of the working battery through components inside the meter.
So the measurement has the following results:
When the red pen of the pointer meter is connected to the positive terminal of the diode and the black pen is connected to the negative terminal (Fig. 1), the diode is connected in the reverse direction and the resistance value is infinity.
When the red pen of the pointer meter is connected to the negative terminal of the diode and the black pen is connected to the positive terminal (Fig. 2), the diode is connected in the forward direction, and the resistance value is very small (tends to conduct).
When the red pen of a digital meter is connected to the positive terminal of the diode and the black pen is connected to the negative terminal (Figure 3), the diode is connected in the forward direction and there is a voltage drop of a few volts.
When the red pen of the digital meter is connected to the negative terminal of the diode and the black pen is connected to the positive terminal (Fig. 4), the diode is connected in the reverse direction and there is no voltage drop.
