Summary of several commonly used methods for detecting resistors

In daily life, resistors are generally referred to as resistors and are one of the important electronic components that have a significant impact on the normal use of circuits in the later stages. We must pay attention to the detection of resistors. Here are some commonly used resistor detection methods compiled by the editor. Let's take a look together!

1： Detection of fixed resistors

1. Select the appropriate range based on the nominal value of the measured resistance, and connect two probes (positive and negative) to the two pins of the resistance to measure the actual resistance value. In order to make the measurement more accurate, 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% radians from the beginning of the full scale. An error of ± 5%, ± 10%, or ± 20% is allowed between the reading and the nominal resistance value, respectively. If the measured resistance value exceeds the error range, it indicates that the resistance value has changed

2. During testing, be careful not to touch the conductive parts of the probes and resistors with your hands, especially when measuring resistors with resistance values of tens of k Ω or more. The tested resistor should be soldered off from the circuit, at least one end should be soldered open to avoid other components in the circuit affecting the test and causing measurement errors; Although the resistance value of the color ring resistor can be determined based on the color ring symbol, it is best to use a multimeter to test its actual resistance value during use.

2： Testing of Cement Resistance

The testing method and precautions for cement resistance are completely the same as those for ordinary fixed resistance testing.

3： Detection of Fused Resistors

Experienced individuals can make judgments based on their experience. When a fuse resistor melts and opens:

If the surface of the fuse resistor is found to be blackened or burnt, it is because the current passing through it exceeds the rated value by many times, causing it to be overloaded;

If there is no trace 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. For the judgment of the quality of a fuse resistor without any trace on the surface, a multimeter R × 1 can be used to measure it. 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. 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 Positive Temperature Coefficient Thermistor (PTC)

During the inspection, use a multimeter in R × 1 gear, which can be operated in two steps:

1. Room temperature detection (indoor temperature around 25 ℃)

Contact the two probes with the two pins of the PTC thermistor to measure its actual resistance value, and compare it with the nominal resistance value. If the difference between the two is within ± 2 Ω, it is considered normal. If the actual resistance value differs significantly from the nominal resistance value, it indicates poor performance or damage.

2. Heating detection

On the basis of normal temperature detection, a heating test can be conducted in one go. A heat source (such as an electric soldering iron) can be placed near the PTC thermistor to heat it, and a multimeter can be used to monitor whether its resistance value increases with the increase of temperature. If so, it means that the thermistor is normal; If there is no change in resistance, it means that its performance has deteriorated and it cannot continue to be used.

Tip: Do not place the heat source too close to or directly in contact with the PTC thermistor during heating detection to prevent it from being burned out.

5： Detection of Negative Temperature Coefficient Thermistor (NTC)

1. Measure the nominal resistance value Rt

The method of measuring NTC thermistor with a multimeter is the same as the ordinary fixed resistance detection method. By selecting the appropriate resistance range based on the nominal resistance value of NTC thermistor, the actual value of Rt can be directly measured. Because NTC thermistors are sensitive to temperature, the following points should be noted during testing:

① When measuring Rt with a multimeter, try to do so at an ambient temperature close to 25 ℃ to ensure the reliability of the test.

② The measured power shall not exceed the specified value to avoid measurement errors caused by current thermal effects.

③ During testing, do not hold the thermistor body with your hands to prevent human body temperature from affecting the test.

2. Estimate the temperature coefficient α t

First, measure the resistance value Rt1 at room temperature t1, then use an electric soldering iron as a heat source and approach the thermistor Rt to measure the resistance value RT2. At the same time, use a thermometer to measure the average temperature t2 on the surface of the thermistor RT at this time before calculating.

6： Testing of Varistors

Measure the forward and reverse insulation resistance between the two pins of the varistor using the R × 1k range of the multimeter. Both values are infinite. Otherwise, it indicates a high leakage current. If the measured resistance is very small, it indicates that the varistor is damaged and cannot be used.

7： Detection of photoresistors

1. Cover the transparent window of the photoresistor with a black piece of paper. At this time, the pointer of the multimeter remains basically stationary, and the resistance value is close to infinity. The higher the resistance value, the better the performance of the photoresistor. If the resistance value is very small or close to zero, it means that the photoresistor has been burned through and damaged, and can no longer be used.

2. Align the transparent window of the photoresistor with a light source, and it can be observed that the pointer of the multimeter swings significantly. If the resistance value decreases significantly, it indicates better performance of the photoresistor; If the resistance value is very high or even infinite at this time, it indicates that the internal open circuit of the photoresistor is damaged and cannot be used anymore.

3. Aim the incident light at the transparent window of the photoresistor, and shake a small black paper on the top of the light shielding window of the photoresistor to allow it to receive intermittent light. At this point, it can be observed that the multimeter pointer swings left and right with the shaking of the black paper; If it is found that the pointer of the multimeter keeps stopping at a certain position and does not swing with the paper, it means that the photosensitive material of the photoresistor has been damaged.

The above are some commonly used resistor detection methods compiled by the editor. Have you learned them? Later, the editor will share with you the testing methods for other electronic components.