The structure of a multimeter and the key points for its use
A multimeter is a multifunctional, multi range portable electrical instrument that can measure DC current, DC voltage, AC voltage, and resistance.
Some can also measure capacitance, inductance, and some parameters of semiconductors (such as β）。
Mastering the use of a multimeter proficiently is a basic skill for electricians, and a multimeter is one of the essential instruments for electricians.
Multimeters can be divided into pointer type multimeter and digital multimeter
Due to the many types of multimeter, it is necessary to prepare for measurement before use.
1. Familiarize yourself with the functions of conversion switches, knobs, sockets, etc. Check the dial symbols. The appearance of "pointer multimeter and digital multimeter" indicates horizontal placement, and "Å" indicates vertical use.
2. Understand the measured electricity level corresponding to each tick mark on the dial.
3. Check if the positions of the red and black probes are correct. Insert the red probe into the "+" socket and the black probe into the "-" socket. Some multimeters also have an AC/DC 2500V high voltage measurement terminal. When measuring high voltage, the black probe does not move. Insert the red probe into the high voltage socket.
4. Mechanical zero adjustment. Rotate the mechanical zero adjustment screw on the multimeter panel to align the pointer with the "0" position on the left end of the dial.
The problem of measuring the forward resistance value of diodes with a multimeter
The multimeter measures the forward resistance of the diode, and different ohmic ranges measure different resistance values.
Diode is a Nonlinear element. It can be seen from its volt ampere characteristic curve that the voltage applied to both ends of the diode is not proportional to the current flowing through the element, that is, its volt ampere characteristic is not a straight line but a curve.
When measuring the forward resistance of a diode using the ohm range of a multimeter, although the R of the ohm range × 1 to R × The internal power supply voltage of 1k is the same, but when measuring at different gears, the internal resistance of the measurement circuit is different.
Therefore, the voltage applied to both ends of the component is also different, resulting in the measured component reflecting different resistance values.
