Why is the diode black positive and red negative when measured by a pointer multimeter pen?
Why is the pointer multimeter pen measuring the diode black positive and red negative
Multimeter head is a DC microampere meter, its deflection direction is related to the direction of the incoming current. That is to say, "red positive black negative", so that the pointer swing is the correct direction, see Figure 1. At this time it is used to measure the DC voltage, current, etc., in this case, the multimeter is equivalent to a measured voltage, current load; selector switch in the first gear.
The wiring diagram of the multimeter when measuring DC voltage and current.
The multimeter has a battery connected in series in the circuit, which is to measure the resistive components, to provide a power supply for the measurement circuit, its head and 1 is common; this time the multimeter is equivalent to a power supply, the measured object is equivalent to the load; see Figure 3, the selector switch is in the 2 position;
3. Measurement of DC voltage and current (the first case) and measurement of resistance (the second case) share a head, the two cases of the current through the head must be in the same direction, that is, the red pen must be the direction of the current into the direction of the black pen is the direction of the current out of the direction of the black pen; and the black pen connected in series with the battery must be the output of the positive pole, then the black pen is the positive pole.
Through the above analysis, we see that in fact the two are unified;
Digital multimeter and pointer multimeter is different at this point; its red positive black negative rule is unchanged;
In the measurement of resistance, the pointer swing amplitude, indicating that the greater the current through the smaller resistance, resistance scale left big and small, which is in line with Ohm's law R = U/I.
