Multimeter for detecting fused resistors
In a circuit, when the fuse is open, 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; If there are no traces on its surface and there is an open circuit, it indicates that the current flowing is just equal to or slightly greater than its rated fuse value. For the judgment of the quality of a fused resistor without any trace on the surface, a multimeter can be used × To ensure accurate measurement, one end of the fuse resistor should be soldered off the circuit in gear 1. If the measured resistance value is infinite, it indicates that the fused resistor has failed and is open circuit. If the measured resistance value differs significantly from the nominal value, it indicates that the resistance has changed and should not be used again. In maintenance practice, it has been found that there are also a few fuse resistors that are broken down and short circuited in the circuit, and attention should also be paid during testing.
Classification of Fusing Resistors
Fusing resistors can be divided into two types: recoverable fuse resistors and disposable fuse resistors.
（1） Recoverable Fusing Resistor
Recoverable fuse resistors are ordinary resistors (or resistance wires) that are soldered in series with low melting point solder and spring type metal ratios (or elastic metal sheets), and then sealed in a cylindrical or square shell. There are several types of shells, including metal and transparent plastic.
Within the rated current, the recoverable fuse resistor acts as a fixed resistor. When an overcurrent occurs in the circuit, the solder joint of the recoverable fuse resistor first melts, causing the spring type metal wire (or elastic metal sheet) to disconnect from the resistor. After troubleshooting the circuit, solder the resistor to the metal wire (or sheet) as required to restore normal use.
The commonly used recoverable fuse resistors include the TH series R × 90 series, etc.
（2） Disposable fuse resistor
A disposable fuse resistor, also known as an irreparable fuse resistor, acts as a fixed resistor during normal circuit operation. When its operating current exceeds the rated current, the fuse resistor will fuse like a fuse to protect the circuit. After a disposable fuse resistor blows, it cannot be repaired in a timely manner and can only be replaced with a new fuse resistor. Disposable fuse resistors can be divided into wire wound fuse resistors and membrane fuse resistors based on the materials used for the resistor body.
1. Wire wound fuse resistors are power type glazed resistors with small resistance values and are typically used in circuits with high operating currents.
During the production process, a part of the power type glazed resistor is wound with thin wire or exposed (without enamel protection layer). In the event of overcurrent faults in the protected circuit, the thin wire or exposed (without glaze layer) part of the resistor will burn off due to overheating, providing protection for the circuit.
2. Membrane fuse resistors are currently the most commonly used fuse resistors, which are divided into various types such as carbon film fuse resistors, metal film fuse resistors, and metal oxide film fuse resistors.
