How to detect resistors

1. Visual inspection

For fixed resistors, first check that the signs are clear, the protective paint is intact, no scorch, no scars, no cracks, no corrosion, and the resistor body is in close contact with the pins. For the potentiometer, it should also be checked that the shaft is flexible, the tightness is appropriate, and the hand feels comfortable. If there is a switch, check whether the switch action is normal.

2. Multimeter detection

①Detection of fixed resistance

Use the electrical resistance of the multimeter to measure the resistance, and select different multipliers of the multimeter for the resistance of different resistance values. For the pointer type multimeter, since the indication of the electrical resistance is nonlinear, the larger the resistance value, the denser the indication. Therefore, to select the appropriate range, the deflection angle of the pointer should be larger, and the indication should be 1/3 to 2/3 of the full scale. , the reading is more accurate. If the measured resistance value exceeds the error range of the resistor, the resistance value is infinite, the resistance value is 0 or the resistance value is unstable, it means that the resistor is broken.

During the measurement, be careful not to touch the two pins of the resistor with the hand holding the resistor, which will cause the resistance presented by the hand to be connected in parallel with the measured resistance, which will affect the accuracy of the measurement. In addition, use a multimeter to electrically block the resistance value of the resistor in the detection circuit when it cannot be charged. In-line detection should first be powered off, then the resistors should be disconnected from the circuit, and then measured.

②Detection of fuse resistance and sensitive resistance

The fuse resistance is generally only a few to tens of ohms. If the measured resistance value is infinite, it has been blown. You can also check the quality of the fuse resistance online, and measure the voltage at both ends to the ground respectively. If one end is the power supply voltage and the other end is 0 volts, the fuse resistance has been blown.

There are many types of sensitive resistors. Taking the thermistor as an example, it is divided into positive temperature coefficient and negative temperature coefficient thermistors. For positive temperature system (PTC) thermistors, the resistance value is generally not large at room temperature. During the measurement, a hot electric soldering iron is used to approach the resistance. At this time, the resistance value should increase significantly, indicating that the resistance is normal. If there is no change, it means The component is damaged, and the negative temperature thermistor is the opposite.

The resistance value of the photoresistor measured by the multimeter is large in the absence of light (hand or object to block the light), and the resistance value indicated by the light meter needle is significantly reduced. If there is no change, the component is damaged.

③ Detection of variable resistors and potentiometers

First, measure whether the resistance value between the two fixed ends is normal. If it is infinite or zero ohms, or the difference from the nominal value is large, and it exceeds the allowable error range, it means that the resistance value is damaged; the resistance value of the resistor body is normal, and then a multimeter The test lead is connected to the sliding end of the potentiometer, and the other test lead is connected to any fixed end of the potentiometer (adjustable resistance). Slowly rotate the shaft handle to observe whether the needle changes smoothly. When it is rotated from one end to the other end, the resistance value is zero. If the ohm changes to the nominal value (or the opposite), and there is no jump or jitter, it means that the potentiometer is normal.

3. Use a bridge to measure resistance

If accurate measurement of the resistance value of a resistor is required, a bridge (digital) test can be used. Insert the resistor into the measuring end of the bridge element, select the appropriate range, and then read the resistance value of the resistor from the display. For example, when using a resistance wire to make a resistor or to process a fixed resistor to obtain a more accurate resistance value, it is necessary to use a bridge to measure the resistance value of the homemade resistor.