How to measure capacitance with pointer multimeter?
Steps
1. Choose the appropriate gear for the electric barrier, generally, if the capacity is below 0.01uF, choose the x10k gear; if it is around 1~10uF, choose the X1k gear; if it is above 47uF, choose the x100 gear or x10 gear.
2. For each test, use a wire to short-circuit the capacitor, and then perform the next test after discharging.
3. Electrolytic capacitors have polarity, and the potential of the positive electrode is higher than that of the negative electrode when used. Since the black test lead is connected to the positive pole of the battery in the watch, the black test lead is connected to the positive pole of the electrolytic capacitor, and the red test lead is connected to the negative pole of the capacitor. A good capacitance performance is that the pointer deflects - down during detection, and then gradually returns to the mechanical zero (that is, the resistance is infinite) position. The amount of deflection of the pointer is related to the capacitance and the resistance position, and the larger the capacity, the larger the deflection. In practice, we must pay attention to the law and accumulate data. The method of adjusting the mechanical zero of the meter head is that when the test pen is neither short-circuited nor measuring any device, use a flat-head screwdriver to align the mechanical zero adjustment notch on the meter head, and turn it left and right to make the pointer point to zero. The performance of a capacitor that has lost its capacity is that the detection pointer does not deflect and does not need to be discharged, and the pointer does not deflect when the test pen is quickly exchanged. The performance of the capacitor that loses part of its capacity is that compared with the standard capacitor, the deflection of the pointer is not in place. It can be judged according to the maximum amplitude of the pointer swing based on experience or referring to the standard capacitor of the same capacity. The reference capacitor does not need to withstand the same voltage value, as long as the capacity is the same, for example, to estimate a 100uF/250V capacitor, a 100uF/25V capacitor can be used as a reference first, as long as the maximum amplitude of their pointer swings is the same, it can be concluded that the capacity is the same . The performance of the leakage capacitor is that the pointer cannot return to the mechanical zero (that is, the resistance is infinite) position. It should be noted that large or small electrolytic capacitors have leakage, low voltage resistance has large leakage, and high voltage resistance has small leakage; use x10k to measure large leakage, and use x1k or less to measure small leakage to determine whether the capacitor is leakage. For capacitors above 1000uF, you can use the Rx10 gear to quickly charge it first, and initially estimate the capacity of the capacitor, and then change to the Rx1k gear to continue measuring for a while. At this time, the pointer should not return, but should stop at or very close to infinity, otherwise There may be a leakage phenomenon. For some capacitors below tens of microfarads, after the Rx1k gear is fully charged, switch to the Rx10k gear to continue measuring. Similarly, the hands should stop at infinity and not return. In addition to electrolytic capacitors, the withstand voltage of ceramic, polyester, metallized paper, and monolithic capacitors is greater than 40V. Test with a multimeter, no matter which block, a good capacitor should not leak. Use a multimeter to measure small-capacity capacitance. You can use the amplification effect of a small-power silicon NPN transistor to block it with a resistor Rx1k. Connect the black test lead to the collector and the red test lead to the emitter. Touch the small capacitor to the collector and the pointer should deflect. The principle is that when the capacitor is charged, the charging current injects the base current into the base, and this current is amplified by the triode, so the pointer deflection is more obvious.
The aluminum electrolytic capacitor structure has strict requirements on the polarity of use. It can be seen from the formula in the figure that the capacity of the plate capacitor is proportional to the dielectric constant of the medium. It is proportional to the relative area of the plates and inversely proportional to the distance between the plates. The positive electrode is aluminum foil. In order to expand the area, the inner surface of the aluminum foil is corroded into unevenness. The medium is an insulator, aluminum oxide, which is very thin. The negative electrode is an electrolyte. The aluminum foil on the right acts as a negative electrode lead. When used correctly, the positive electrode is connected to a high potential, and the negative electrode is connected to a low potential. Under the action of direct current, the electrolyte can decompose oxygen atoms, and form alumina with the positive aluminum foil to maintain insulation. When used incorrectly, the positive electrode is connected to a low potential, and the negative electrode is connected to a high potential. Under the action of direct current, the electrolyte will corrode aluminum oxide, destroy insulation, and in the lightest case, electric leakage, severe heat generation, or even burst. Therefore, you must pay attention to the polarity when using it, and it must be energized frequently for aging if it is not used for a long time.
