Several Common Resistor Testing Methods

In daily life, resistors are one of the important electronic components, the normal use of the circuit later has a great impact, so we should pay attention to the detection of resistors.

I: Detection of Fixed Resistors

1. According to the size of the nominal value of the measured resistance to choose the appropriate range, with two pens (not divided into positive and negative) were connected to the two pins of the resistor to measure the actual resistance value. In order to make the measurement more accurate, the pointer should be made to indicate the value as far as possible to fall into the middle position of the scale, that is, the beginning of the full scale within the range of 20% to 80% arc. Readings and the nominal resistance value between the allowable ± 5%, ± 10% or ± 20% error. If the measured resistance value exceeds the error range, it means that the resistance value of the value of the change.

2. In the test, pay attention to the hands do not touch the meter pen and the conductive part of the resistor, especially in the measurement of more than tens of kΩ resistance to pay more attention to this point. The resistor to be tested from the circuit to weld down, at least to weld open a head, to avoid other components in the circuit on the test to have an impact on the measurement error; color ring resistor resistance value can be determined according to the color ring logo, but in the use of the best or use a multimeter to test the actual resistance value.

II: Detection of Cement Resistors

Cement resistor testing methods and precautions and ordinary fixed resistance testing methods are exactly the same.

III: Detection of Fusing Resistors

Generally experienced people can make a judgment based on experience, when the fusing resistor fuses open-circuit:

1. If you find the surface of the fusing resistor black or burnt, because the current through it exceeds the rated value of many times the load caused by overloading;

2. If there is no trace on the surface and open circuit, it means that the current flowing through it is just equal to or slightly greater than its rated fusing value. For the surface of the fusing resistor without any trace of good or bad judgment, can be measured with the help of a multimeter R × 1 block, in order to ensure the accuracy of the measurement, the fusing resistor should be welded from the circuit at one end. If the measured resistance to infinity, the fusing resistor has failed open-circuit, if the measured resistance and the nominal value of the difference is very far, indicating that the resistance value, should not be used again. Found in the maintenance practice, there are a few fusing resistors in the circuit was broken short-circuit phenomenon, detection should also be noted.

IV: Detection of Positive Temperature Coefficient Thermistor (PTC)

Detection, with a multimeter R × 1 block, the specific operation can be divided into two steps:

1. Room Temperature Detection (indoor temperature of about 25 ℃)

The two pens will contact the two pins of the PTC thermistor to measure its actual resistance, and compared with the nominal resistance, the difference between the two within ± 2Ω is normal. If the difference between the actual resistance value and the nominal resistance value is too large, it means that its performance is poor or damaged.

2.Temperature Testing

On the basis of normal temperature detection, can be carried out at a time of heating detection, will be a heat source (such as a soldering iron) near the PTC thermistor on its heating, while using a multimeter to monitor its resistance value with the increase in temperature and increase, if yes, on behalf of the thermistor is normal; if the resistance value does not change, on behalf of the performance of its deterioration, can not continue to use.

Tips: Do not allow the heat source and the PTC thermistor to be too close or directly contact with the thermistor during the heating test, in order to prevent it from being burned.

V:Detection of Negative Temperature Coefficient Thermistor (NTC)

1.Measure the Nominal Resistance Value Rt

The method of measuring NTC thermistor with multimeter is the same as that of ordinary fixed resistor. According to the nominal resistance value of NTC thermistor, the actual value of Rt can be measured directly by choosing suitable resistance block. Because NTC thermistor is very sensitive to temperature, the following points should be noted when testing:

① When measuring Rt with a multimeter, do it when the ambient temperature is close to 25℃ as far as possible to ensure the credibility of the test.

② Measurement power should not exceed the specified value, so as to avoid the current thermal effect caused by the measurement error.

③ Do not pinch the thermistor body with your hand during the test to prevent the body temperature from affecting the test.

2.Estimation of Temperature Coefficient

Measure the resistance value Rt1 at room temperature t1, and then use soldering iron as heat source, close to the thermistor Rt, measure the resistance value RT2, and at the same time, use a thermometer to measure the average temperature of the surface of the thermistor RT t2 and then calculate.

VI: Detection of Varistor

With a multimeter R × 1k block to measure the positive and negative insulation resistance between the two pins of the varistor, are infinite, otherwise, the leakage current is large. If the measured resistance is very small, it means that the varistor is damaged and cannot be used.

VII: Detection of Photosensitive Resistors

1. The transmittance window of the photosensitive resistor should be covered with a piece of black paper, at this time, the pointer of the multimeter should remain basically unchanged, and the resistance value should be close to infinity; the larger the resistance value is, the better the performance of the photosensitive resistor is; if the resistance value is very small or close to zero, it means that the photosensitive resistor has been burnt through and damaged, and can not be used any more.

2. Align the transmittance window of the photosensitive resistor with a light source, then you can find the amplitude of the multimeter's pointer swing is relatively large, if the resistance value is significantly reduced, representing the better performance of the photosensitive resistor; if the resistance value is very large or even infinity, it means that the photosensitive resistor has been damaged by the internal open circuit and can not be used further.

3. Align the incident light to the photoresistor light transmission window, with a small piece of black paper in the photoresistor shading window on the upper part of the shaking, so that its intermittent light, then you can find the multimeter pointer is with the shaking of the black paper and the left and right swing; if you find that the multimeter pointer has been parked in a certain position does not swing with the shaking of the paper and the swing, which means that the photoresistor light-sensitive materials have been damaged.

The above are some commonly used resistor detection methods, have you learned?