How to use a multimeter to check the quality of capacitors
Capacitors, commonly referred to as capacitors, have the ability to hold charges and are represented by the letter C. Definition 1: A capacitor, as the name suggests, is a 'container for storing electricity' and a device that holds an electric charge. English name: capacitor. Capacitors are one of the widely used electronic components in electronic devices, widely used in circuit isolation, coupling, bypass, filtering, tuning circuits, energy conversion, control, and other aspects. Definition 2: A capacitor is composed of any two conductors (including wires) that are insulated from each other and located very close to each other.
Capacitors are different from capacitors. Capacitance is a fundamental physical quantity, with the symbol C and the unit F (Farads).
General formula C=Q/U for parallel plate capacitors: Inter plate electric field strength E=U/d, capacitor capacitance determination formula C=ε S/4 π kd
With the rapid development of electronic information technology, the updating speed of digital electronic products is getting faster and faster. The production and sales of consumer electronic products, mainly flat panel TVs (LCD and PDP), laptops, digital cameras, etc., continue to grow, driving the growth of the capacitor industry. And it has driven the development of related materials and equipment industries, making China a major producer of capacitors worldwide.
1. Detection of fixed capacitors
A detects small capacitors below 10pF
Due to the small capacity of fixed capacitors below 10PF, using a multimeter for measurement can only qualitatively check for leakage, internal short circuits, or breakdown phenomena. When measuring, a multimeter with R × 10k range can be used, and two probes can be connected to either pin of the capacitor. The resistance value should be infinite. If the resistance value (pointer swinging to the right) is zero, it indicates that the capacitor is damaged by leakage or internal breakdown.
B detects whether there is charging phenomenon in the fixed capacitor of 10PF~0.01 μ F, and then judges its quality.
The multimeter is set to R × 1k gear. The beta values of both transistors are above 100, and the penetration current should be small. 3DG6 and other models of silicon triodes can be used to form composite transistors. The red and black probes of the multimeter are respectively connected to the emitter e and collector c of the composite tube. Due to the amplification effect of the composite transistor, the charging and discharging process of the measured capacitor is amplified, which increases the amplitude of the multimeter pointer and facilitates observation. It should be noted that during testing, especially when measuring capacitors with smaller capacities, the pins of the tested capacitor should be repeatedly switched to contact points A and B in order to clearly see the swing of the multimeter pointer.
For fixed capacitors above 0.01 μ F, the R × 10k range of a multimeter can be used to directly test whether the capacitor has a charging process and whether there is an internal short circuit or leakage. The capacitance of the capacitor can be estimated based on the amplitude of the pointer swinging to the right.
2. Testing of electrolytic capacitors
Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, appropriate measurement ranges should be selected for different capacities during measurement. Based on experience, in general, capacitors between 1 and 47 μ F can be measured in the R × 1k range, while capacitors greater than 47 μ F can be measured in the R × 100 range.
Connect the red probe of the multimeter to the negative terminal and the black probe to the positive terminal. At the moment of initial contact, the multimeter pointer will deflect significantly to the right (for the same electrical barrier, the larger the capacity, the greater the swing), and then gradually turn left until it stops at a certain position. At this point, the resistance value is the forward leakage resistance of the electrolytic capacitor, which is slightly greater than the reverse leakage resistance. Practical experience has shown that the leakage resistance of electrolytic capacitors should generally be above several hundred k Ω, otherwise they will not function properly. In the test, if there is no charging phenomenon in both forward and reverse directions, that is, the meter needle does not move, it indicates that the capacity has disappeared or there is an internal circuit breaker; If the measured resistance is very small or zero, it indicates that the capacitor has a large leakage or has been broken down and damaged, and cannot be used anymore.
For electrolytic capacitors with unclear positive and negative electrode markings, the above method of measuring leakage resistance can be used to distinguish them. First, measure the leakage resistance arbitrarily, remember its size, and then exchange the probes to measure another resistance value. The one with the highest resistance value between the two measurements is the forward connection method, where the black probe is connected to the positive pole and the red probe is connected to the negative pole.
D uses a multimeter resistor to charge the electrolytic capacitor in both forward and reverse directions. Based on the magnitude of the pointer's rightward swing, the capacity of the electrolytic capacitor can be estimated.
