1. Appearance inspection

For fixed resistance, first check the logo is clear, the protection paint is intact, no burning, no scars, no cracks, no corrosion, resistance body and pin close contact.For the potentiometer should also check the shaft flexible, appropriate tightness, feel comfortable.If there is a switch, check whether the switch action is normal.

2. Multimeter testing

(1) Fixed resistance detection

The electrical barrier of the multimeter is used to measure the resistance. For the resistance of measuring different resistance values, the multiple multiples of the multimeter are selected.For pointer type multimeter, because the electrical block number is nonlinear, the greater the resistance value, the more dense the number, so choose the appropriate range, should make the needle deflection Angle bigger, indicating in 1/3 ~ 2/3 full range, reading more accurate.If the measured resistance exceeds the error range of the resistance, the resistance value is infinite, the resistance value is 0 or the resistance value is unstable, the resistance is broken.

During the measurement, it should be noted that the hand holding the resistor should not contact with the two pins of the resistor. In this way, the resistance presented by the hand will be in parallel with the resistance under test, which will affect the accuracy of measurement.In addition, the multimeter is used to detect the electricity in the circuit when it cannot be charged

The resistance value of the resistor.On - line testing should first disconnect the power, then disconnect the resistance from the circuit, and then measure.

(2) Fuse resistance and sensitive resistance detection

Fuse resistance general resistance value only a few to dozens of Euro, if measured resistance value is infinite, it has been blown.The fuse resistance can also be detected online, and the voltage on both ends of the fuse can be measured respectively. If one end is the power supply voltage and the voltage on one end is 0 V, the fuse resistance has been fuses.

There are many kinds of sensitive resistors. Taking thermistors as an example, thermistors are divided into positive and negative temperature coefficients.For positive temperature system (PTC) thermistors, the general resistance value is not large at room temperature, in the measurement with the hot electric soldering iron close to the resistance, the resistance value should be significantly increased, indicating that the resistance is normal, if there is no change, indicating component damage, negative temperature thermistors are the opposite.

In the absence of light (cover the light with hand or object), the multimeter has a high resistance value, and the light needle indicates that the resistance value has a significant decrease.If there is no change, the component is damaged.

(3) Variable resistance and potentiometer detection

First, measure whether the resistance value between the two fixed ends is normal. If it is infinite or zero ohm, or it differs greatly from the nominal value and exceeds the allowable range of error, it indicates that it has been damaged.Resistance value is normal, and then a multimeter pens and potentiometer sliding side, the other pens and answer the potentiometer (adjustable resistance) any of the fixed end, varied slowly rotating shaft, observe whether the clock is smooth, when from one end of the screw to the other end, resistance from zero the change to the nominal value (or the opposite), and there is no jump or the phenomenon such as jitter, explain potentiometer is normal, if in the process of spinning jump or dithering phenomenon, that sliding resistance is to the poor contact.

3. Use a bridge to measure resistance

If it is required to accurately measure the resistance value of the resistor, the test can be carried out via a bridge (digital).The resistance value of the resistor can be read from the display by inserting the resistor into the measuring end of the bridge element and selecting the appropriate range.For example, when a resistance wire is used or a fixed resistor is processed to obtain a more accurate resistance value, a bridge must be used to measure the resistance value of the self-made resistor.