Can a multimeter measure capacitance? How to use a multimeter to detect capacitance

　　Multimeter Overview

　　Multimeter, also known as multiplexer, multimeter, three-meter, complex meter, etc., is an indispensable measuring instrument in power electronics and other departments. It is generally used to measure voltage, current and resistance. Multimeters are divided into pointer multimeters and digital multimeters according to the display mode. It is a multifunctional and multi-range measuring instrument. Generally, multimeters can measure DC current, DC voltage, AC current, AC voltage, resistance and audio level, etc. Some can also measure AC current, capacitance, inductance and some parameters of semiconductors (such as β).

　　Basic functions of multimeter

　　A multimeter can be used not only to measure the resistance of the object being measured, but also the AC and DC voltages and DC voltages. Some multimeters can even measure the main parameters of transistors and the capacitance of capacitors. Being fully proficient in the use of a multimeter is one of the most basic skills in electronic technology. Common multimeters include pointer multimeters and digital multimeters. A pointer multimeter is a multifunctional measuring instrument with a meter head as the core component, and the measured value is read by the meter head pointer. The measured value of a digital multimeter is directly displayed in digital form on the LCD screen, which is easy to read, and some also have a voice prompt function. A multimeter is an instrument that uses a common meter head and integrates a voltmeter, an ammeter, and an ohmmeter.

　　The DC current range of the multimeter is a multi-range DC voltmeter. The voltage range can be expanded by connecting a closed-circuit voltage divider resistor in parallel to the meter head. The DC voltage range of the multimeter is a multi-range DC voltmeter. The voltage range can be expanded by connecting a voltage divider resistor in series to the meter head. Different voltage divider resistors have different corresponding ranges. The meter head of the multimeter is a magnetoelectric measurement mechanism, which can only pass DC and use a diode to convert AC into DC, thereby realizing the measurement of AC.

　　How a Multimeter Works

　　The basic principle of a multimeter is to use a sensitive magnetoelectric DC ammeter (microammeter) as the meter head. When a small current passes through the meter head, there will be a current indication. However, the meter head cannot pass a large current, so some resistors must be connected in parallel or in series to the meter head for shunting or voltage reduction, so as to measure the current, voltage and resistance in the circuit.

　　Multimeter Operating Procedures

　　1. Be familiar with the functions of the multimeter before use, and correctly select the gear, range and test lead jack according to the object to be measured.

　　2. When the size of the measured data is unknown, the range switch should be set to the maximum value first, and then switched from the large range to the small range so that the instrument pointer indicates more than 1/2 of the full scale.

　　3. When measuring resistance, after selecting the appropriate magnification, touch the two test leads together to make the pointer point to zero. If the pointer deviates from zero, adjust the "zero adjustment" knob to return the pointer to zero to ensure accurate measurement results. If zero adjustment is not possible or the digital display gives a low voltage alarm, check in time.

　　4. When measuring the resistance of a circuit, the power supply of the circuit under test must be cut off and measurements must not be made while the circuit is powered.

　　5. When using a multimeter for measurement, pay attention to the safety of both the person and the instrument. Do not touch the metal part of the test lead with your hands during the test, and do not switch the gear switch while energized to ensure accurate measurements and avoid accidents such as electric shock and burning of the instrument.

　　Precautions for using a multimeter

　　1. Before using the multimeter, you should first perform "mechanical zero adjustment", that is, when there is no electrical quantity to be measured, make the multimeter pointer point to the position of zero voltage or zero current.

　　2. When using a multimeter, do not touch the metal part of the test lead with your hands. This can ensure accurate measurement and personal safety.

　　3. When measuring a certain amount of electricity, you cannot change gears while measuring, especially when measuring high voltage or high current. Otherwise, the multimeter will be damaged. If you need to change gears, you should disconnect the test leads first and then measure after changing gears.

　　4. When using the multimeter, it must be placed horizontally to avoid errors. At the same time, it is also necessary to avoid the influence of external magnetic fields on the multimeter.

　　5. After using the multimeter, the conversion switch should be set to the maximum AC voltage. If it is not used for a long time, the battery inside the multimeter should be removed to prevent the battery from corroding other components in the meter.

　　Can a multimeter measure capacitance? How to use a multimeter to detect capacitance

　　1. Use a pointer multimeter to detect capacitance

　　1.1. Detection of fixed capacitors

　　(1) Detection of fixed capacitors with a capacity of more than 0.01 pF Set the pointer multimeter to the R&TImes;10k ohm range and perform ohm zeroing. Then use the red and black test leads of the multimeter to touch the two pins of the capacitor respectively and observe the changes in the multimeter pointer, as shown in Figure 1. If the multimeter pointer swings slightly to the right at the moment the test leads are connected, and then returns to infinity, after replacing the test leads and measuring again, the pointer also swings to the right and then returns to infinity, then it can be determined that the capacitor is normal; If the multimeter pointer swings to near "0" at the moment the test leads are connected, it can be determined that the capacitor is broken down or has serious leakage; If the pointer does not return to infinity after swinging at the moment the test leads are connected, it can be determined that the capacitor has leakage; If the multimeter pointer does not swing twice, it can be determined that the capacitor is open circuit.

　　(2) Detection of fixed capacitors with a capacity less than 0.01 pF When detecting small capacitors below 10 pF, because the capacitance is too small, a multimeter can only be used to check whether it has leakage, internal short circuit or breakdown: When measuring, use the multimeter R& TI mes;10k block, connect the two test leads to the two pins of the capacitor at random, and the resistance should be infinite. If the measured resistance is zero, it can be determined that the capacitor is leaking or damaged or has internal breakdown.

Figure 1 Detection of fixed capacitance above 0.01 pF

　　(3) The following method can be used to detect 10pF～0.01tF fixed capacitors. Set the multimeter to the R& TI mes;10k position, and select two transistors 3DC6 (or 9013) with a value greater than 100 to form a composite tube. The circuit schematic is shown in Figure 2. The charging current of the measured capacitor is amplified by the amplification effect of the composite tube to increase the swing amplitude of the multimeter pointer. Connect the measured capacitor between the base b and the collector c of the composite tube, and connect the red and black test leads of the multimeter to the emitter e and collector c of the composite tube respectively. If the pointer of the multimeter swings slightly and then returns to infinity, it means that the capacitor is normal; if the pointer does not move or cannot return to infinity, it means that the capacitor is damaged. During the test operation, especially when measuring a smaller capacitance capacitor, repeatedly switch the contact points of the capacitor pins to be measured to clearly see the swing of the multimeter pointer.

Figure 2 Schematic diagram of the test circuit composed of composite tubes

　　1.2. Detection of electrolytic capacitors

　　The capacity of electrolytic capacitors is much larger than that of general fixed capacitors. When measuring, choose the appropriate range for different capacities. In general, the capacitance between 1 and 47 pF can be measured with the R& TI mes;1k block; the capacitance greater than 47 ptF can be measured with the R×100 block. The smaller the capacitance, the larger the blocking ratio should be. Before measuring, the capacitor should be fully discharged, that is, the two pins of the electrolytic capacitor should be short-circuited to discharge the residual charge in the capacitor. The two pins of the capacitor can be short-circuited with the multimeter probe. The schematic diagram of the capacitor discharge method is shown in Figure 3. Large-capacity capacitors must be discharged with the metal part of a screwdriver. After the capacitor is fully discharged, connect the red probe of the pointer multimeter to the negative pole and the black probe to the positive pole. At the moment of connection, the pointer of the multimeter should deflect to the right at a large angle, and then gradually return to the left until it stops at a certain position. The resistance value at this time is the forward insulation resistance of the electrolytic capacitor, which should generally be above several hundred kiloohms. Replace the test leads and the pointer repeats the previous phenomenon. The final resistance indicated is the reverse insulation resistance of the capacitor, which should be slightly smaller than the forward insulation resistance. The detection diagram of the electrolytic capacitor is shown in Figure 4.

Figure 3 Schematic diagram of capacitor discharge method

Figure 4 Schematic diagram of electrolytic capacitor detection

　　In the above measurement, if the multimeter pointer does not move during measurement, it means that the capacitor capacity has disappeared or the internal circuit is broken; if the forward and reverse insulation resistance of the capacitor is very small or zero, it means that the capacitor has a large leakage current or an internal short circuit and cannot be used. For electrolytic capacitors with unclear positive and negative pole markings, the method of measuring insulation resistance can be used to distinguish them, that is, first use the two test pens of the multimeter to touch the two pins of the capacitor and measure the insulation resistance of the capacitor. After replacing the test pens, measure again. The larger value is the forward insulation resistance. At this time, the black test pen is connected to the positive pole of the capacitor.