The use of a multimeter in maintenance
1. Digital multimeter
On the multimeter, you will see a conversion knob as shown in the figure, which refers to the gear of the secondary quantity
V~: represents the gear for measuring AC voltage
V -: represents the gear for measuring DC voltage
MA: Refers to the gear used to measure the DC voltage
Ω R: represents the gear used to measure resistance
HFE: represents the gear for measuring resistance
The red pen on the multimeter indicates the positive pole of the external circuit, while the black pen indicates the negative pole of the external circuit
Advantages: Anti magnetic, convenient reading, accurate digital display
Mechanical multimeter
The appearance of a mechanical multimeter is somewhat different from that of a digital meter, but their shift knobs are similar and their gear positions are also basically the same
On the mechanical watch, you will see a dial as shown in the picture, with eight scales on the dial:
The scale marked with "Ω" is used for measuring resistance
The "~" mark is used to measure AC/DC voltage and DC current
The scale marked with "HFE" is used for measuring transistors
The scale marked with "LI" measures the current and voltage of the load
The scale marked with "DB" measures the level
3. Use of a multimeter
① Digital multimeter: Before measuring, set the gear to the measurement position. It should be noted that the range marked on the gear is the maximum value
② Mechanical multimeter: The method for measuring current and voltage is the same as the mathematical formula, but when measuring electronegativity, the reading needs to be multiplied by the value on the gear to obtain the measurement value. For example, if the current gear is set to "X100" and the reading is 200, the measurement question is set to "200X100=20000 Ω=20K", and the "Ω" scale on the dial is from left to right, from large to small, while the others are from left to right, from small to large
4. Precautions:
① Only mechanical watches with "zero point" adjustment are available. Before using the watch, check if the pointer is pointing to the left "zero position". If not, use a small screwdriver to slowly rotate the "starting zero position" correction screw in the center of the watch case, so that the pointer is pointing to the zero position
② When using a multimeter, the machinery should be placed horizontally to ensure proper functioning
③ Before testing, it is necessary to determine the measurement content and turn the range conversion knob to the corresponding measurement gear shown to avoid burning the meter head. If the size of the measured physical quantity is not known, it is necessary to start testing from a large range
④ The pen should be inserted correctly into the corresponding socket
⑤ During the testing process, do not rotate the gear change knob arbitrarily
⑥ After use, be sure to adjust the gear change knob to the range range of AC voltage
⑦ When measuring DC voltage and current, attention should be paid to the positive and negative terminals of the voltage, the direction of current flow, and the correct connection with the probe
