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.

（1） Recoverable Fusing Resistor

The commonly used recoverable fuse resistors include the TH series R × 90 series, etc.

（2） Disposable fuse resistor

1. Wire wound fuse resistors are power type glazed resistors with small resistance values and are typically used in circuits with high operating currents.

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.