1. Accurate measurement method of fixed resistor
For fixed resistors, their detection is not only a basic skill in electronic maintenance, but also a key step to ensure the normal operation of the circuit. First of all, when using a multimeter to measure resistance, the correct operation method is to connect two test probes to both ends of the resistor. During this process, the positive and negative polarities of the probes do not affect the measurement results. In order to enhance the accuracy of measurement, it is important to select the appropriate range. The nominal value of the resistor should guide the selection of the range to ensure that the measurement pointer falls in the middle of the range, that is, between 20% and 80% of the full range, so as to use the more finely graduated part of the ohm stop to reduce reading errors. .
The allowable error range of the resistor varies according to its accuracy level, which are ±5%, ±10%, and ±20%. This means that when a measurement is taken, the deviation between the measured value and the nominal value of the resistor should be within this range. Measurements outside this range may indicate that the resistance has changed and no longer meets its original specifications.
In actual operation, some details need to be paid attention to to ensure the accuracy of measurement. For example, when measuring higher resistance values (above tens of kΩ), avoid touching the test probe and the conductive part of the resistor directly with your hands to prevent the human body resistance from affecting the measurement results. In addition, before measurement, the resistor should be soldered off the circuit board and at least one end disconnected to avoid interference from other components in the circuit.
2. Detection strategy of cement resistance
Due to its special structure and materials, cement resistors are widely used in situations requiring high power dissipation. The method of detecting cement resistance is essentially the same as that of ordinary fixed resistance. This emphasizes the versatility of basic resistance measurement techniques and also reminds operators that they can apply the same basic principles for troubleshooting when dealing with different types of resistance.
3. Diagnostic Technology of Fused Resistors
As a safety protection component, the fuse resistor can automatically disconnect when the circuit is overloaded to avoid more serious damage. When the surface of a fuse resistor appears blackened or scorched, it usually means that the current flowing through it far exceeds the rated value. Conversely, if a fuse resistor shows no trace on its surface but is open, this may indicate that the current is only slightly higher than its rated fuse rating. The R×1 scale of the multimeter is an effective tool to judge the quality of the fuse resistor. When measuring, one end of the fuse resistor should be disconnected from the circuit. If the resistance value is infinite, it indicates that the fuse resistor has failed. In addition, during actual maintenance, it is occasionally found that the fuse resistor is broken down and short-circuited, which also needs to be paid attention to during inspection.
4. Detection and evaluation of potentiometers
As a common variable resistor, the potentiometer's performance directly affects the adjustment function of the circuit. The first step in checking the potentiometer is to check whether the rotation of the knob is smooth and whether the switch operation is flexible. In addition, the sound produced when the switch is operated is also a criterion for judging its quality. When using a multimeter to measure resistance, you should select an appropriate range based on the resistance of the potentiometer, and verify whether it is consistent with the nominal value by measuring the resistance at both ends. The rotation of the potentiometer's shaft should be smooth, and the resistance value should change continuously during the rotation without jumping. If a poor internal contact of the potentiometer is found during the test, the potentiometer should be considered damaged.