Multimeter - Negative Temperature Coefficient Thermistor (NTC) Testing
The method of measuring NTC thermistor with a multimeter is the same as that of measuring ordinary fixed resistor, i.e. the actual value of Rt can be measured directly by choosing a suitable resistor block according to the nominal resistance value of NTC thermistor. However, since NTC thermistor is very sensitive to temperature, the following points should be noted during the test: A?Rt is measured by the manufacturer at the ambient temperature of 25℃, so the measurement of Rt with a multimeter should be carried out when the ambient temperature is close to 25℃ to ensure the credibility of the test.B?Measurement of the power should not exceed the specified value, so as to avoid the current thermal effect caused by the measurement error.C?Pay attention to the correct operation. When testing, do not pinch the thermistor body with your hand to prevent the body temperature from affecting the test.
(Estimate the temperature coefficient αt
How to use the multimeter resistance gear is introduced first in the room temperature t1 measured resistance value Rt1, and then use the soldering iron as a heat source, close to the thermistor Rt, measured resistance value RT2, at the same time with a thermometer to measure the average temperature of the surface of the thermistor RT at this time t2 and then calculate.
The use of multimeter resistance file is introduced 7?The detection of varistor. Use the multimeter R × 1k block to measure the positive and negative insulation resistance between the two pins of the varistor, are infinite, otherwise, it means that the leakage current is large. If the measured resistance is very small, it means that the varistor is damaged and cannot be used.
Photoresistor detection. A? With a piece of black paper will be photoresistor light transmission window cover, this time the multimeter's pointer basically stays motionless, the resistance value is close to infinity. The larger the value, the better the performance of the photoresistor. If this value is very small or close to zero, the photoresistor has been burned through the damage, can not continue to use.
Aim a light source at the transmittance window of the photoresistor, then the multimeter pointer should have a large swing, the resistance value decreases significantly. The smaller the value, the better the performance of the photoresistor. If this value is very large or even infinity, indicating that the photoresistor internal open-circuit damage, and can not continue to use.
The photoresistor transmittance window aligned with the incident light, with a small piece of black paper in the photoresistor shading window on the upper part of the shaking, so that its intermittent light, when the multimeter pointer should be with the shaking of the black piece of paper and the left and right oscillation. If the multimeter pointer always stops at a certain position does not swing with the shaking of the piece of paper, indicating that the photoresistor photosensitive material has been damaged.
