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. Below are some commonly used resistor detection methods compiled by the editor. Let's take a look together

First: Detection of fixed resistors

1. Select an appropriate range based on the nominal value of the measured resistance, and use two probes (regardless of positive or negative) to connect to the pins at both ends of the resistor to measure the actual resistance value.

. 2. During testing, be careful not to touch the conductive part of the probe and resistance, especially when measuring resistance values of tens of k Ω or above. The detected resistance should be soldered off from the circuit, at least one head 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 based on the color ring symbol, it is best to use a multimeter to test its actual resistance value when using it

Second: Detection of cement resistance

The detection method and precautions for cement resistance are completely the same as ordinary fixed resistance detection methods.

Three: Detection of Fusing Resistors

Generally, experienced individuals can make judgments based on experience. When the fusing resistor is blown open:

1. If the surface of the fusing resistor is found to be black or burnt, it is because the current passing through it exceeds the rated value many times, causing it to be overloaded If there are no traces on the surface and there is an open circuit, it indicates that the current flowing is just equal to or slightly greater than its rated fuse value. For the judgment of the quality of a fused resistor without any trace on the surface, a multimeter R can be used × To ensure accurate measurement, one end of the fuse resistor should be soldered off the circuit in gear 1. If the measured resistance value is infinite, it indicates that the fused resistor has failed and is open circuit. If the measured resistance value differs significantly 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

Four: Detection of Positive Temperature Coefficient Thermistors (PTC)

During detection, use a multimeter R × First gear, specific operation can be divided into two steps:

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

Measure the actual resistance value of the two contacts of the PTC thermistor's two pins and compare it with the nominal resistance value. The difference between the two is within ± 2 Ω, which is 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 room temperature detection, a heating detection can be carried out at once. A heat source (such as an electric soldering iron) is placed close to the PTC thermistor to heat it, and a multimeter is used to monitor whether its resistance value increases with the increase of temperature. If so, it indicates that the thermistor is normal; If the resistance value does not change, it indicates that its performance has deteriorated and cannot be used anymore

Tip: During heating detection, do not let the heat source come too close to or directly contact the PTC thermistor to prevent it from being burned out

Five: Detection of Negative Temperature Coefficient Thermistors (NTC)

1. Measure the nominal resistance value Rt

The method of measuring NTC thermistors with a multimeter is the same as that of ordinary fixed resistance detection. Selecting an appropriate resistance gear based on the nominal resistance value of NTC thermistors can directly measure the actual value of Rt.

① When measuring Rt with a multimeter, try to measure it as close to the ambient temperature of 25 ℃ as possible to ensure the reliability of the test ② The measured power should not exceed the specified value to avoid measurement errors caused by current thermal effects During the test, do not hold the thermistor body with your hands to prevent human body temperature from affecting the test 2. Estimation of temperature coefficient α T

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

VI: Detection of Varistors

R using a multimeter × Measure the forward and reverse insulation resistance between the two pins of the varistor at 1k gear, both of which 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

Seven: Detection of photosensitive resistors

1. Cover the transparent window of the photosensitive resistor 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 photosensitive resistor. If the resistance value is very small or close to zero, it means that the photosensitive resistor has been burned through and damaged, and can no longer be used 2. Align the transparent window of the photosensitive resistor with a light source, and at this point, it can be observed that the pointer of the multimeter swings significantly. If the resistance value is significantly reduced, it indicates that the performance of the photosensitive resistor is better; If the resistance value at this time is large or even infinite, it indicates that the internal open circuit damage of the photosensitive resistor is no longer usable 3. Aim the incident light at the transparent window of the photosensitive resistor, and use a small piece of black paper to shake the upper part of the photosensitive resistor's shading window, causing it to receive intermittent light. At this point, it can be observed that the pointer of the multimeter swings left and right with the shaking of the black paper; If it is found that the pointer of the multimeter has been parked in a certain position and does not swing with the shaking of the paper, it means that the photosensitive material of the photosensitive resistor has been damaged