Testing Methods and Experience of Multimeter Resistors:
1. Detection of fixed resistors. A? Connect two probes (regardless of positive or negative) to the pins at both ends of the resistor to measure the actual resistance value. In order to improve measurement accuracy, the range should be selected based on the nominal value of the measured resistance. Due to the nonlinear relationship of the ohmic scale, the middle section of the scale is relatively fine. Therefore, the pointer should be positioned as close as possible to the middle section of the scale, which is within the range of 20% to 80% radians from the beginning of the full scale, in order to make the measurement more accurate. Depending on the level of resistance error. An error of ± 5%, ± 10%, or ± 20% is allowed between the reading and the nominal resistance value, respectively. If it does not match and exceeds the error range, it indicates that the resistance value has changed. B? Attention: During testing, especially when measuring resistance values above tens of k Ω, do not touch the conductive parts of the probe and resistance with your hands; The tested resistance should be soldered off from the circuit, at least one head should be soldered open to prevent other components in the circuit from affecting the test and causing measurement errors; Although the resistance value of the color ring resistor can be determined by the color ring symbol, it is best to use a multimeter to test its actual resistance value when using it.
2. Detection of cement resistance. The method and precautions for detecting cement resistance are identical to those for detecting ordinary fixed resistors.
3. Detection of fused resistors. In a circuit, when the fuse resistor is blown open, a judgment can be made based on experience: if the surface of the fuse resistor is found to be black or burnt, it can be concluded that its load is too heavy, and the current passing through it exceeds the rated value many times; If there are no traces on its surface and there is an open circuit, it indicates that the current flowing is just equal to or slightly greater than its rated fuse value. For the judgment of the quality of a fused resistor without any trace on the surface, a multimeter R can be used × To ensure accurate measurement, one end of the fuse resistor should be soldered off the circuit in gear 1. If the measured resistance value is infinite, it indicates that the fused resistor has failed and is open circuit. If the measured resistance value differs significantly from the nominal value, it indicates that the resistance has changed and should not be used again. In maintenance practice, it has been found that there are also a few fuse resistors that are broken down and short circuited in the circuit, and attention should also be paid during testing.
4. Detection of potentiometers. When checking the potentiometer, the first step is to rotate the knob to see if it rotates smoothly, whether the switch is flexible, whether the "click" sound is clear when the switch is on or off, and listen to the sound of friction between the internal contact points of the potentiometer and the resistor body. If there is a "rustle" sound, it indicates poor quality. When using a multimeter for testing, first select the appropriate resistance gear of the multimeter based on the resistance value of the tested potentiometer, and then perform the testing according to the following method.
Use the ohmic range of a multimeter to measure both ends of "1" and "2", and the reading should be the nominal resistance value of the potentiometer. If the pointer of the multimeter does not move or the resistance value differs significantly, it indicates that the potentiometer is damaged.
Check if the contact between the movable arm of the potentiometer and the resistor is good. Measure both ends of "1" and "2" (or "2" and "3") using the ohm range of a multimeter, and rotate the potentiometer shaft counterclockwise to a position close to "off". At this point, the smaller the resistance value, the better. Slowly rotate the shaft handle clockwise again, the resistance value should gradually increase, and the pointer in the meter head should move smoothly. When the shaft handle is turned to the extreme position "3", the resistance value should be close to the nominal value of the potentiometer. If the pointer of the multimeter jumps during the rotation of the potentiometer shaft, it indicates that there is a fault with poor contact at the movable contact point.
