The use and precautions of multimeters and oscilloscopes
(1) Pointer multimeter
(1) Mechanical zero position adjustment: Before use, you should first check whether the pointer is at zero position. If it is not at zero position, adjust the zero position adjuster to bring the pointer to zero position.
(2) Connect the test leads correctly: the red test lead should be inserted into the jack marked "+", and the black test lead should be inserted into the jack marked "-". When measuring DC current and DC voltage, the red test lead is connected to the positive pole of the measured voltage and current, and the black test lead is connected to the negative pole.
When using the ohm block "Ω" to determine the polarity of the diode, note that the "+" jack is connected to the negative pole of the battery in the meter, and the "-" jack is connected to the positive pole of the battery in the meter.
(3) When measuring voltage, the multimeter should be connected in parallel with the circuit under test; when measuring current, the circuit under test should be disconnected and the multimeter should be connected in series to the circuit under test. Note: When measuring current, you should estimate the size of the current being measured and select the correct range. The MF500 fuse is 0.3A ~ 0.5A, and the current being measured cannot exceed this value. Some multimeters have a 10A range, which can be used to measure larger currents.
(4) Range conversion: The power should be cut off first, and it is not allowed to change the range while it is powered; place it in the correct position according to what is being measured. Do not use the current block or ohm block to measure the voltage, otherwise the multimeter will be damaged.
(5) Reasonably select the measuring range: when measuring voltage and current, the meter needle should be deflected to more than 1/2 or 2/3 of the full scale; when measuring resistance, the meter needle should be deflected to near the center scale (the design of the electrical barrier is based on The center scale is standard).
When measuring AC voltage and current, please note that the measured AC voltage and current must be sinusoidal AC voltage and current, and the frequency of the measured signal cannot exceed the specifications in the instruction manual.
When measuring AC voltage below 10V, the reading should be marked with a special 10V scale, whose scales are not equally spaced.
(6) When measuring resistance, the meter should be zeroed first. The method is to short-circuit the two test leads and adjust the "zero" knob so that the pointer points to the zero point (note that the zero scale of ohms is on the right side of the dial). If the zero point cannot be adjusted, it means that the battery voltage in the multimeter is insufficient and a new battery needs to be replaced. When measuring a large resistance, do not touch the resistor with both hands at the same time to prevent measurement errors caused by the human body resistance being connected in parallel with the resistance being measured. Every time the range is changed, zero must be reset. If the above method cannot be used to zero, it is possible that the multimeter's wire-wound resistor (a resistor with a resistance of about a few ohms) is burned out and needs to be disassembled for repair and correction.
There are multiple scale lines on the dial, corresponding to different measured objects. When reading, the value should be read on the corresponding scale line. To improve measurement accuracy, try to keep the pointer in the middle position.
Reading of measured value: Multiply the reading marked by the pointer by the range magnification during measurement to get the measured value. When measuring resistance, be careful not to touch the two test leads or the metal ends of the resistance being measured, so as not to introduce human body induced resistance and reduce the reading, especially for the R×10K test.
(7) After using the multimeter, place the transfer switch in the maximum AC voltage position to avoid damaging the meter.
(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 multimeter batteries: ordinary AA (1.5v) and laminated batteries (9v). Among them, 9v is used to measure resistance above 10k and determine the leakage of small capacitors.
(9) Since the resistance range R×10K of the multimeter uses a 9V battery, components with very low withstand voltage cannot be detected.
