The use and precautions of multimeter and oscilloscope
(1) Pointer type multimeter
(1) Mechanical zero position adjustment: Before use, check whether the pointer is at zero position. If it is not, adjust the zero position adjuster to adjust the pointer to zero position.
(2) Connect the probe correctly: The red probe should be inserted into the socket marked with "+", and the black probe should be inserted into the socket marked with "-". When measuring DC current and DC voltage, the red probe is connected to the positive pole of the measured voltage and current, and the black probe is connected to the negative pole.
When using the ohm gear "Ω" to determine the polarity of a diode, it is important to note that the "+" socket is the negative terminal of the battery inside the meter, and the "-" socket is the positive terminal of the battery inside the meter.
(3) When measuring voltage, the multimeter should be connected in parallel with the circuit being tested; When measuring current, disconnect the circuit being tested and connect a multimeter in series in the circuit being tested. Attention: When measuring the current, the size of the measured current should be estimated and the correct range should be selected. The fuse of MF500 type is 0.3A~0.5A, and the measured current cannot exceed this value. Some multimeters have a 10A gear and can be used to measure larger currents.
(4) Range conversion: Power should be turned off first, and changing range with live power is not allowed; According to the measurement being placed in the correct position, do not use the current or ohm range to measure voltage, otherwise it will damage the multimeter.
(5) Reasonable selection of measuring range: When measuring voltage and current, the pointer should be deflected to more than 1/2 or 2/3 of the full scale; When measuring resistance, the pointer should be deflected to the vicinity of the center scale (the design of the resistance gauge is based on the center scale).
When measuring AC voltage and current, it is important to note that the measured voltage and current must be sinusoidal, and the frequency of the measured signal must not exceed the specifications in the manual.
When measuring AC voltage below 10V, a dedicated 10V scale should be used to indicate the reading, and its scale is not evenly spaced.
(6) When measuring resistance, the meter should be zeroed first. The method is to short circuit the two probes and adjust the "zero" knob to make the pointer point at zero (note that the zero scale of the ohm is on the right side of the dial). If the zero point cannot be adjusted, it indicates that the battery voltage in the multimeter is insufficient and a new battery needs to be replaced. When measuring large resistance, both hands should not touch the resistance at the same time to prevent measurement errors caused by parallel connection between the human body resistance and the measured resistance. Every time the range is changed, it needs to be reset to zero. If the above methods cannot be zeroed, there is a possibility that the winding resistance of the multimeter (with a resistance value of about a few ohms) may burn out, and it needs to be disassembled for repair and correction.
There are multiple scale lines on the dial, corresponding to different measurements. When reading, the values should be taken on the corresponding scale lines. To improve measurement accuracy, try to keep the pointer in the middle position as much as possible.
Reading of measurement value: Multiply the reading indicated by the pointer during measurement by the range multiplier to obtain the measured value. When measuring resistance, be careful not to touch the two probes or the metal end of the measured resistance with your hands to avoid introducing human induced resistance and reducing the reading, especially for the R × 10K range test, which has a significant impact.
(7) After using the multimeter, place the conversion switch in the maximum AC voltage position to avoid damaging the instrument.
(8) When the multimeter is not used for a long time, the battery should be removed to prevent battery leakage, corrosion, and damage to the internal parts of the multimeter. There are two types of batteries for the multimeter: ordinary No. 5 (1.5V) and stacked battery (9V). 9V is used to measure resistance above 10k and distinguish leakage of small capacitors.
(9) Due to the use of a 9V battery in the resistance range R × 10K of the multimeter, it is not possible to detect components with very low withstand voltage values.
