When the parameter mark of the resistor comes off for some reason or the exact resistance value is not known, it needs to be measured with an instrument. The resistance of common carbon film, metal film resistors and wire wound resistors can be directly measured with the resistance of ordinary pointer multimeters. The following points should be noticed during specific measurements:

Reasonable selection of range. First set the multimeter function to “Ω”. Since the resistance scale of the pointer multimeter is a non-uniform scale, you must choose a suitable range so that the indicated value of the measured resistance is as close as possible to 0 on the scale. The scale line is at the position of 2/3 of the whole journey, which can improve the accuracy of the measurement. For resistors with hundreds of thousands of ohms, X10K should be selected for measurement.

Pay attention to zero. The so-called "zero adjustment" is to short the two test leads of the meter, and adjust the "zero adjustment" knob to make the pointer of the meter point to the "0Ω" position on the dial.

Second, the test of the thermistor

Negative temperature coefficient thermistors are currently used more in circuits. To judge the performance of the thermistor, while measuring its resistance, pinch the thermistor with your fingers to increase the temperature, or use an electric soldering iron to heat it (be careful not to let the electric iron contact the resistance Device). If its resistance value decreases with increasing temperature, it indicates that its performance is good: if it does not change or changes little with temperature, it indicates that its performance is bad or damaged.

Third, the test of the potentiometer

Test requirements: The total resistance value of the potentiometer should meet the marked value. The central sliding end of the potentiometer should be in good contact with the resistor body. Its dynamic noise and static noise should be as small as possible, and its switch should be accurate and reliable.

Detection method: first measure the total resistance value of the potentiometer, that is, the resistance value between the two ends should be the nominal value, and then measure the contact between the center end piece and the resistor. Connect one test lead to the center welding piece of the potentiometer, and the other test lead to any of the other two ends. Slowly rotate the handle from one extreme position to the other extreme position, and the resistance value should be from zero ( (Or nominal value) continuously changes to the nominal value (or zero).