The multimeter's reading of the capacitance value changes all the time.
Either the circuit is unstable or the multimeter is almost out of power.
The refresh rate displayed by the digital multimeter is approximately 3 times per second, so it is normal for it to change. But if it jumps around and something is wrong, it may be due to poor contact. Generally, it is the test leads and the circuit under test, or the test leads and the multimeter itself. There may also be poor welding of the multimeter jack, contact problems with the multimeter transfer switch, insufficient battery, etc.
The steps to use a digital multimeter to test the quality of the capacitor are as follows:
1. To determine the polarity, first adjust the multimeter to 100 or 1K ohm. Assume that one pole is positive, connect the black test lead to it, and the red test lead to the other pole. Note the resistance value, and then discharge the capacitor, that is, let the two poles Make contact, and then change the test leads to measure the resistance. The black test lead with the larger resistance is connected to the positive electrode of the capacitor.
2. Adjust the multimeter to the appropriate ohm level. The principle of gear selection is: 1μF capacitor uses 20K gear, 1-100μF capacitor uses 2K gear, and larger than 100, μF uses 200 gear.
3. Then use the red pen of the multimeter to connect the positive pole of the capacitor, and the black pen to the negative pole of the capacitor. If the display slowly increases from 0, and finally displays the overflow symbol 1, the capacitor is normal. If it always displays 0, the capacitor is short-circuited internally. If 1 is displayed, the capacitor is internally open.
How to use a multimeter
1. Before use, you should be familiar with the various functions of the multimeter, and correctly select the gear, range and test lead socket according to the object being measured.
2. When the size of the measured data is unknown, you should first set the range switch to the maximum value, and then switch from the large range to the small range, so that the meter pointer indicates more than 1/2 of the full scale.
3. When measuring resistance, after selecting the appropriate magnification level, touch the two test leads to make the pointer point at the zero position. If the pointer deviates from the zero position, adjust the "zero adjustment" knob to return the pointer to zero to ensure accurate measurement results. . If it cannot be zeroed or the digital display issues a low-voltage alarm, it should be checked in time.
4. When measuring the resistance of a certain circuit, the power supply of the circuit under test must be cut off, and the measurement must not be carried out while it is powered on.
5. When using a multimeter for measurement, pay attention to the safety of the person and the instrument equipment. During the test, you are not allowed to touch the metal part of the test pen with your hands, and it is not allowed to switch the gear switch while the power is on to ensure accurate measurement and avoid accidents such as electric shock and burning of the meter. .
