How to use a multimeter to measure different resistances
1. Fixed resistance testing method
Connect the two probes (positive and negative) to the two pins 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.
Testing experience:
1) Due to the non-linear relationship of the resistance scale; The distribution in the middle section is relatively fine, so the pointer should be placed as close as possible to the middle position of the scale, that is, within the range of 20% to 80% of the arc at the beginning of the full scale, in order to make the measurement more accurate. Depending on the level of resistance error, there may be an error of ± 5%, ± 10%, or ± 20% between the reading and the nominal resistance value, respectively. If it does not match and exceeds the error range, it indicates that the resistance has changed value.
2) When testing, especially when measuring resistors with resistance values of tens of k ohms or more, do not touch the conductive parts of the probes and resistors with your hands. When the tested resistor is soldered off from the circuit, at least one end 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 measure its actual resistance value during use.
For the detection of cement resistance, as it is usually a fixed resistance, the method of detecting cement resistance is completely the same as detecting ordinary fixed resistance.
2. Test method for fuse resistance
1) In a circuit, when a fuse resistor is blown open, a judgment can be made based on experience; If the surface of the fuse resistor is found to be blackened or burnt, it can be concluded that its load is too heavy, and the current passing through it exceeds the rated value by many times; If there are no traces on the surface and the circuit is open, it indicates that the current flowing is exactly equal to or slightly greater than its rated melting value.
2) For the judgment of the quality of a fuse resistor with no surface traces, the Rxl range of a multimeter can be used for measurement. To ensure accurate measurement, one end of the fuse resistor should be soldered off from the circuit. If the measured resistance value is infinite, it indicates that the fuse resistor has failed and opened. If the measured resistance value is far from the nominal value, it indicates that the resistance has changed and should not be used again.
Testing experience: In practice, there are also a few cases where fuse resistors are broken down or short circuited in circuits.
3. Potentiometer testing method
1) When checking a potentiometer, the first step is to turn the knob and try whether it rotates smoothly and whether the switch is flexible. Check if the "click" sound is crisp when the switch is turned on or off, and listen for the sound of friction between the internal contact points of the potentiometer and the resistor. If there is a "rustling" sound, it indicates poor quality.
2) When testing with a multimeter, first select the appropriate resistance range of the multimeter based on the resistance value of the potentiometer being tested, and then perform the test according to the following method.
Measure the resistance of "1" and "3" ends with a multimeter, 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. Use the resistance range of a multimeter to measure the ends of "l" and "2". Rotate the potentiometer shaft 2 counterclockwise to a position close to "off". The smaller the resistance value, the better. Slowly rotate the shaft clockwise again, the resistance value should gradually increase, and the pointer in the meter head should move steadily. When the shaft handle is rotated to the extreme position "3", the resistance value should be close to the nominal value of the potentiometer (similar when measuring the ends of "2" and "3").
Test experience: If the pointer of a multimeter jumps during the rotation of the potentiometer shaft, it indicates that there is a poor contact between the movable contacts.
