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Judge the resistor is damaged in the circuit
2020-01-14
 
The resistor is composed of a resistor body, a skeleton, and a lead-out terminal (the resistor body and the skeleton of the solid-core resistor are combined into one), and it is only the resistor that determines the resistance value. Its main physical characteristic is to change electrical energy into thermal energy. It can also be said that it is an energy-consuming element, and current passes through it to generate internal energy. The resistor usually plays the role of voltage division and current distribution in the circuit. For signals, both AC and DC signals can pass through resistors. So how to judge that it is damaged in the circuit? What are the common detection methods?

Cause of resistance damage

There are two general reasons for resistance damage: external and internal.

There are many external reasons. The current is too large, which causes burnout or resistance change. The soldered circuit board is deformed due to external force, which causes the resistance to break (especially in surface-mounted resistors). Even if the heat is not discharged, the resistor will be easily damaged in an overheated environment ...

There are several common internal causes: the quality of the resistor is rough, and the material is uneven, causing local resistance to change. The power selection is very close to the maximum power point. When instantaneous interference occurs, the resistance is damaged ...

Common resistor detection methods:

Detection of damage to fixed resistors

In the detection of fixed resistors, the situation of resistance can be accurately measured by measuring directly with a multimeter, so that it can be judged whether there is a fault in the resistance. Although there is no skill at all, it is important to note that in order to ensure the accuracy of the measurement value, you need to select the range according to the measurement needs and try to control the reading as accurately as possible. In this regard, because the ohm scale has a non-linear relationship, in order to improve the accuracy, you must also try to control the pointer to fall to the middle position of the dial to make the measurement more accurate and avoid errors affecting the judgment. Generally speaking, if the difference between the measured value and the actual value is within 20% of the maximum value, then the resistance is normal, and if it exceeds this range, then the resistance is damaged.

Detection of thermistor damage

In the thermistor detection work, the temperature change method is usually used to assist the detection. Take a thermistor with a positive coefficient as an example. When testing, first use the multimeter's R × 1 block to measure the heat at room temperature. The actual resistance value of the varistor can be used for preliminary damage detection by comparing this resistance value with the approved value. However, it should be noted that in order to ensure that there is no other failure of the resistance, everyone needs to perform further testing under the condition of heating. Generally speaking, when the normal temperature thermistor works normally, its resistance value will increase as the temperature rises. In order to ensure this function is normal, everyone should observe the resistance change in the heating resistor to determine the sensitivity of the thermistor. Happening. To determine the operation of the thermistor, both of the above steps are essential.

Detection of Photoresistor Damage

Finally, let's take a look at the detection method of the photoresistor. For the photoresistor, to ensure the smooth detection, you need to first block the transparent port of the resistor with an opaque material. Under normal circumstances, At this time, when resistance measurement is performed, the resistance value will not change, and the resistance value should be close to infinity. If not, then the photoresistor has been damaged. In addition, for further confirmation, you need to observe the change in resistance through the stimulation of the light source. If the resistance is significantly reduced when the light source is not available, it also indicates that the resistance has been damaged. The detection of these two aspects is a necessary process. Only when all are guaranteed, can the working condition of the resistor be explained.
 
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