Principle of Testing Fusing Resistors with a Multimeter
The main parameters of a fuse resistor include nominal resistance, rated power, allowable deviation, etc. The concept of each parameter is basically similar to that of a general color ring resistor. In general, only its nominal resistance value is indicated on a fuse resistor, and other parameters are not represented. The nominal resistance values are represented by color rings, and their specific representation method is similar to that of ordinary color ring resistors. But there are differences depending on the place of origin, some have four color rings, while others only have one color ring. For a fuse resistor with four color rings, its reading method can be based on the law of ordinary color ring resistance. The first and second rings represent the first two digits of the resistance value, the third ring represents the multiplication factor, and the fourth ring represents the error. For a fuse resistor with only one color ring, the color of the color ring represents different resistance values. For example, black represents 10Q, red represents 2.2Q, and white represents 1Q.
This article mainly discusses two types of detection for fuse resistors, one is open circuit and the other is in circuit. The following is a detailed introduction:
1. Open circuit detection of fuse resistors using a multimeter
The open circuit detection method of the fuse resistor using a multimeter is shown in the figure. Measure the resistance between the two pins of a multimeter using the ohm range. The resistance value measured when the fuse resistor is blown should be infinite. If the resistance value of the measured fuse resistor is much greater than its nominal resistance value, it indicates that the measured fuse resistor has changed value and is damaged. Generally speaking, fuse resistors do not experience short circuit faults.
2. In circuit detection of fuse resistors using a multimeter
In a circuit, when a fuse resistor is blown open, a judgment can be made based on experience. If the surface of the fuse resistor is found to be blackened or burnt, it can be concluded that its load is too heavy, which is caused by the current passing through it exceeding the rated value by many times; If there is no trace on its surface and it opens, 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, the circuit can be powered on, and then the DC voltage between the two ends of the fuse resistor to ground can be measured with the help of a multimeter voltage range. When the measured voltage on one end is 0V and the voltage on the other end is normal, it means that the resistor has been opened. During road testing, the resistance of the resistor can also be measured using a multimeter with the R * 1 Ω range. The specific testing method is shown in the figure. 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 significantly different from the nominal resistance value, it indicates a change in resistance value and should not be used again. In maintenance practice, it has been found that there are also a few cases of fuse resistors breaking down and short circuiting in the circuit, which should also be taken into account during testing.
