Fuse resistor detection technique using a multimeter
A fuse resistor is a special component that has the dual functions of a resistor and a fuse. It is represented by the letter "RF" or "R" in the circuit.
Selection of fuse resistors
When selecting, its dual performance should be considered, and parameters such as its resistance value and power should be selected according to the specific requirements of the circuit. It is necessary to ensure that it can fuse quickly when it is overloaded, and it must also ensure that it can work stably for a long time under normal conditions. If the resistance value is too large or the power is too large, neither can play a protective role.
Measuring method with multimeter for detection of fuse resistor
In the circuit, when the fuse is disconnected, a judgment can be made based on experience: if the surface of the fuse resistor is found to be black or burnt, it can be concluded that its load is too heavy, and the current passing through it exceeds the rated value many times; An open circuit without any trace indicates that the current flowing is just equal to or slightly greater than its rated fusing value. For the judgment of the quality of the fuse resistor without any traces on the surface, it can be measured with the r×1 gear of the multimeter. To ensure accurate measurement, one end of the fuse resistor should be soldered off the circuit. If the measured resistance value is infinite, it means that the fuse resistor has failed to open circuit. If the measured resistance value is far from the nominal value, it means that the resistance value has changed and it is not suitable for use. In the maintenance practice, it is found that a small number of fuse resistors are broken down and short-circuited in the circuit, and attention should also be paid to it during detection.
Classification of fuse resistors
Fuse resistors can be divided into two types: resettable fuse resistors and one-time fuse resistors.
(1) Resettable fuse resistor
Recoverable fuse resistors are welded in series with ordinary resistors (or resistance wires) with low melting point solder and spring metal ratios (or elastic metal sheets), and then sealed in a cylindrical or square housing. There are several types of shells such as metal and transparent plastic.
Within the rated current, resettable fuse resistors act as fixed resistors. When an overcurrent occurs in the circuit, the solder joint of the resettable fuse resistor melts first, so that the spring-type metal wire (or elastic metal sheet) is disconnected from the resistor. After troubleshooting the circuit fault, weld the resistor and the metal wire (or metal sheet) as required, and then normal use can be resumed.
Commonly used resettable fuse resistors include TH series R×90 series and so on.
(2) Disposable fuse resistor
Disposable fuse resistors are also called non-recoverable fuse resistors. They act as fixed resistors when the circuit is working normally. When the operating current exceeds the rated current, the fuse resistors will blow like a fuse to protect the circuit. , After the one-time fuse resistor is blown, it cannot be repaired in time, and can only be replaced with a new fuse resistor. Disposable fuse resistors can be divided into wire-wound fuse resistors and film fuse resistors according to the material used in the resistor body.
1. Wire-wound fuse resistors Wire-wound fuse resistors are power-type glazed resistors with small resistance values, and are usually used in circuits with large operating currents.
During the production process, a part of the power-type glazed resistor is wound with a thin wire or exposed (with no enamel protection layer). When an overcurrent fault occurs in the protected circuit, the thin wire or exposed part of the resistor ( The unglazed part) will be blown due to overheating to protect the circuit.
2. Film type fuse resistors Film type fuse resistors are currently the most used fuse resistors, and they are divided into carbon film fuse resistors, metal film fuse resistors and metal oxide film fuse resistors.
