A multimeter measures current, voltage and resistance. What level to set and how to read it?
Observe and understand the structure of a multimeter.
There are many types of multimeters with different shapes, but the basic structure and usage are the same.
A multimeter must have a meter and a selector switch on the board. There is also an ohm level zero adjustment knob and a test lead socket. The following describes the functions of each part:
(1) Header
The meter head of the multimeter is a sensitive ammeter. The dial on the watch head is printed with various symbols, scales and numerical values. The symbol A-V-Ω indicates that this meter is a multimeter that can measure current, voltage and resistance. There are multiple scale lines printed on the dial. The one marked with "Ω" on the right end is the resistance scale line. The right end is zero and the left end is ∞. The scale value distribution is uneven. The symbol "-" or "DC" represents direct current, "~" or "AC" represents alternating current, and "~" represents the scale line shared by AC and DC. The several rows of numbers under the scale line are the scale values corresponding to the different gears of the selector switch.
There is also a mechanical zero adjustment knob on the watch head to correct the pointer to point to zero at the left end.
(2) Selector switch
The multimeter's selector switch is a multi-position rotary switch. Used to select measurement items and range. General multimeter measurement items include: "mA"; DC current, "V": DC voltage, "V": AC voltage, "Ω": resistance. Each measurement item is divided into several different ranges for selection.
(3) Test leads and test lead sockets
The pens are divided into red and black. When using, insert the red test lead into the jack marked with "+" and the black test lead into the jack marked with "-".
How to use a multimeter
(1) Before using the multimeter, you should do the following:
1. The multimeter is placed horizontally.
2. You should check whether the needle stops at the zero position at the left end of the dial. If there is deviation, use a small screwdriver to gently turn the mechanical zero adjustment knob on the meter head to make the meter hand point to zero.
3. Insert the test leads into the test lead jack according to the above requirements.
4. Turn the selector switch to the corresponding item and range. It's ready to use.
(2) After using the multimeter, you should:
1. Pull out the test leads.
2. Turn the selector switch to the "OFF" position. If there is no such position, turn it to the maximum range of AC voltage, such as the "1000V" position.
3. If it is not used for a long time, the battery in the watch should be removed to prevent battery electrolyte from leaking and corroding the internal circuit.
(1) Measuring DC voltage
The measurement steps are:
1. Select the measurement range. The DC voltage range of the multimeter is marked with "V" and has five ranges: 2.5 volts, 10 volts, 50 volts, 250 volts and 500 volts. Select the range according to the power supply voltage in the circuit. Since the power supply voltage in the circuit is only 3 volts, the 10 volt range is selected. If you don't know the voltage, you should first measure with the highest voltage level and gradually switch to the lower voltage level.
2. Measurement methods. The multimeter should be connected in parallel with the circuit under test. The red pen should be connected to the connection between the circuit under test and the positive pole of the power supply, and the black pen should be connected to the connection between the circuit under test and the negative pole of the power supply.
3. Correct reading. Observe the dial carefully. The DC voltage scale line is the second scale line. When using the 10V scale, you can directly read the measured voltage value by using the third row of numbers under the scale line. When taking a reading, your eyes should be facing the pointer.
