How to measure the varistor and Photo resistor by using a pointer multimeter?

One, the test method.

   Using the multimeter R × 1 or R × 10k shields, the resistance of varistor is measured, and then it is measured twice after changing the pen. Under normal conditions, the value of resistor measured twice should be infinity. If the measured resistance value is close to 0 or has a certain resistance value, the varistor has breakdown damage or leakage damage.

    Second, the problems that need to be paid attention to.

To detect varistors, the highest blocking position of the multimeter should be used. At room temperature, the resistance between the two pins of the varistor should be infinitely large, and the digital multimeter display will display the overflow symbol "1". If the resistance value is not infinite, the breakdown voltage of the varistor is lower than the 9V (or 15V) voltage of the battery inside the multimeter (this varistor is rare) or the resistor has been damaged or the leak is bad.

The method of detecting Photo resistor is good or bad.

    When detecting Photo resistors, the resistance retaining switch of the multimeter should be dialed to the appropriate position according to the bright resistance value of Photo resistor.

    First, the method of detection.

    First measure the resistance value of Photo resistor when there is light irradiation, the smaller this value, the better Photo resistance performance, if the resistance value is very large, that Photo resistance internal open circuit damage, can no longer be used.

    Then, a thick piece of paper covering Photo's resistor is tightly covered. If Photo's resistor is normal, it will cause a sharp increase in the value of resistance because of no illumination. The larger the resistance value detected, the better the resistance performance of Photo will be. If the      photosensitive resistor is spoiled or damaged, the resistance value will change little or no change. Under normal conditions, the resistance value of Photo resistor changes greatly after receiving light.

In addition, in the presence of light, if the measured Photo resistor resistance value of zero or infinite (the digital multimeter shows overflow symbol "1" or "OL"), the Photo resistor can also be determined to be damaged (internal shortcuts or open circuit.

    Second, the choice of light source.

    The light source used to detect the bright resistance of Photo resistor is different depending on the type of Photo resistor.

 (1). For visible photosensitive resistors, use an incandescent light bulb to illuminate a light source.

 (2). For the UV Photo resistor, you can use the detector's UV lamp to illuminate the light source.

 (3). For infrared photosensitive resistors, the infrared emitting tube in the TV remote control can be used as the light source.