The life of the patch capacitor has always been a problem that many people wonder about. Many people do not know how much life the patch capacitor has and how much life it has been used. Today, the patch capacitor manufacturer will introduce how to infer the life of the capacitor. First, the service life of the capacitor can be calculated through the voltage acceleration and temperature acceleration coefficients. The steps are as follows:

The external ambient temperature and the applied voltage at the time of use of the product can be formulated as parameters. In general, the Arrhenius rule is widely used in acceleration formulas, and we can use the following formula to make simple calculations.
47_01cn.PNG Based on this formula, the service life of the product in the actual use environment can be calculated by accelerating the test under more severe conditions (higher temperature, higher voltage). Here, let's compare the accelerated test of monolithic ceramic capacitors with the assumed environment of actual product use. In the accelerated test of the capacitor, the endurance test time is regarded as LA, and the number of years in the actual use environment is regarded as LN, which is used in the above formula.
Durability test conditions assume that the use of environmental voltage acceleration coefficient temperature acceleration coefficient corresponding years TA = 85 C VA = 20V LA = 1000h TN = 65 C VN = 5V n = 4 θ = 8 LN =? H In this way, we can calculate the service life of the product to be 1448155h (≈ 165 years!). The voltage acceleration coefficient and temperature acceleration coefficient used in the calculation will be different from the type and structure of the ceramic material, but the acceleration calculation formula can be used to verify the product service life in the long-term actual use environment in a relatively short time by using the test results.
The identification and application of capacitive elements are as follows:
First: the detection of capacitors
The main faults of the capacitor are: breakdown, short circuit, leakage, capacity reduction, deterioration and breakage.
One. Appearance inspection
Observe that the appearance should be intact, the surface should be free of cracks, dirt and corrosion, the signs should be clear, and the lead-out electrode should be free of folding damage; the adjustable capacitor should be rotated flexibly, there should be no collision or rubbing between the moving and fixed plates, and the rotation between the couplings should be synchronized.
II. Test leakage resistance
With a multimeter ohmic gear (R× 100 or R× 1k gear), contact the stylus to the two leads of the capacitor. When it is just mounted, the pointer of the meter head will swing and then gradually return to the position of R = ∞, which is the charge and discharge phenomenon of the capacitor (this phenomenon cannot be observed for capacitors below 0.1μF). The greater the swing of the pointer, the greater the capacity. The value indicated by the pointer after it is stable is the leakage resistance value. Its value is generally several hundred to several giga ohms, the greater the resistance, the better the insulation performance of the capacitor. During detection, if the meter pointer points to or is close to the ohm zero point, it means that the capacitor is short-circuited. If the pointer does not move and always points to R = ∞, it means that the capacitor is open-circuited or invalid.
Capacitors above 5000pF can be discriminated by multimeter resistance, and small-capacity capacitors below 5000pF should be discriminated by special measuring instruments.
Three. Polarity Detection of Electrolytic Capacitors
The positive and negative polarities of electrolytic capacitors are not allowed to be connected incorrectly. When the polarity mark cannot be identified, it can be detected and judged according to the characteristics of large leakage resistance during forward connection and small leakage resistance during reverse connection. The leakage resistance value is measured twice before and after the test pen is exchanged. When the resistance value is large once, the black test pen contacts the positive electrode. (Because the black pen is connected to the positive pole of the battery in the table)
Four. Detection of bump or leakage of variable capacitor
The multimeter is set to R× 10 gear, the two pens are respectively placed on the moving piece and the fixed piece of the variable capacitor, and the moving piece is slowly rotated. If the pointer of the meter head is always stationary, there will be no touching phenomenon and no leakage. If the pointer of the meter head points to 0Ω when rotated to a certain angle, it means the touch piece here. If the pointer of the meter head has certain indication or slight swing, it indicates leakage.
Second: the selection method of capacitor
One. Choose the right model
According to the circuit requirements, it is generally used for low-frequency coupling, bypass decoupling, etc. When the electrical performance requirements are low, paper capacitors, electrolytic capacitors, etc. can be used.
The coupling capacitor of the transistor low-frequency amplifier is an electrolytic capacitor of 1~22 μF. Bypass capacitor is selected according to the working frequency of the circuit. For example, in low frequency circuit, emitter bypass capacitor is electrolytic capacitor with a capacity of 10 ~ 220μF. In intermediate frequency circuit, 0.01 ~ 0.1μF paper medium, metallized paper medium, organic film capacitor, etc. can be selected. High frequency porcelain dielectric capacitor should be selected in high frequency circuit; If it is required to work at high temperature, glass glaze capacitor should be selected. In the power supply filter and decoupling circuit, can choose the electrolytic capacitor. Because in these occasions, the performance of the capacitor is not high, as long as the volume is not large, the capacity is enough.
For variable capacitors, it should be determined that single or multiple variable capacitors should be used according to the series of capacitance unified adjustment, and then the corresponding variety of capacitors should be determined according to the requirements of capacity change range, capacity change curve, volume, etc.
II. Reasonable Determination of Capacitor Capacity and Error
The value of the capacitor capacity must be selected according to the specified nominal value.
There are many kinds of error levels of capacitors. In low-frequency coupling, decoupling, power filter and other circuits, capacitors can be ± 5%, ± 10%, ± 20% and other error levels, but in oscillation circuits, delay circuits, and tone control circuits, The accuracy of capacitors is slightly higher; in various filters and various networks, high-precision capacitors are required.
Third: the choice of pressure value
In order to ensure the normal operation of the capacitor, the resistance value of the selected capacitor should not only be greater than the actual working voltage, but also have enough leeway. Generally, the capacitor with withstand voltage value more than twice the actual working voltage should be selected.
Fourth: pay attention to the temperature coefficient of the capacitor, high frequency characteristics and other parameters
In the oscillation circuit of the oscillation components, phase shift network components, filters, etc., should be selected small temperature coefficient of the capacitor to ensure its performance.
chip capacitor is introduced:
Patch capacitor type of laminated capacitor is a one-time high-temperature sintering is also printed by the electrode (inner electrode) of the ceramic dielectric film in a staggered manner.
chip capacitor internal structure profile:
The chip capacitor mainly includes three parts: ceramic dielectric, inner electrode and end electrode. Among them, the main function of ceramic medium is to polarize the dielectric energy storage under the action of electric field. When the polarization rate changes when the electric field changes, the response speed and polarization rate of the electric field change are different due to the different main polarization types of different media types.