Multimeter measurement method for detecting fuse resistors
A fuse resistor is a special component that has the dual functions of a resistor and a fuse. It is represented in the circuit by the letters "RF" or "R".
Selection of fuse resistors
When selecting, its dual performance should be considered, and parameters such as resistance and power should be selected according to the specific requirements of the circuit. It is necessary not only to ensure that it can quickly fuse when overloaded, but also to 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, it will not be able to protect.
Multimeter measurement method for detecting blown resistors
In the circuit, after the fuse is disconnected, you can make a judgment based on experience: if the surface of the fuse resistor is found to be black or burnt, it can be concluded that it is overloaded and the current passing through it exceeds the rated value many times; if the surface If there is no trace but an open circuit, it means that the current flowing is just equal to or slightly greater than its rated fuse value. To judge the quality of the fuse resistor without any trace on the surface, you can use the r×1 scale of the multimeter to measure it. To ensure accurate measurement, one end of the fuse resistor should be welded off the circuit. If the measured resistance value is infinite, it means that the fuse resistor has failed and is open circuit. If the measured resistance value is far from the nominal value, it means that the resistance value has changed and it should not be used anymore. During the maintenance practice, it was found that a small number of fuse resistors were broken down and short-circuited in the circuit. This should also be paid attention to during detection.
Fuse resistor classification
Fuse resistors can be divided into two types: recoverable fuse resistors and disposable fuse resistors.
(1) Recoverable fuse resistor
The recoverable fuse resistor is an ordinary resistor (or resistance wire) that is welded together in series with a low melting point solder and a spring metal ratio (or elastic metal sheet), and then sealed in a cylindrical or square casing. The shells are available in 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 joints of the resettable resistor melt first, causing the spring-loaded wire (or elastic metal piece) to disconnect from the resistor. After eliminating the circuit fault, weld the resistor and metal wire (or metal sheet) as required, and then normal use can be resumed.
Commonly used recoverable fuse resistors include TH series, R×90 series, etc.
(2) One-time fuse resistor
The one-time fuse resistor is also called a non-recoverable fuse resistor. It functions as a fixed resistor when the circuit is working normally. When its operating current exceeds the rated current, the fuse resistor will melt like a fuse to protect the circuit. , after the one-time fuse resistor is blown, it cannot be repaired immediately and can only be replaced with a new fuse resistor. Disposable fuse resistors can be divided into wirewound fuse resistors and film fuse resistors according to the materials used in the resistor body.
1. Wirewound fuse resistor Wirewound fuse resistor is a power type glazed resistor with a small resistance value and is usually used in circuits with large operating current.
During the production process, a part of the power type glazed resistor is wound with a thin wire or the exposed part (without an enamel protective layer). When an overcurrent fault occurs in the protected circuit, the thin wire part or the exposed part of the resistor (not coated with an enamel protective layer) The unglazed part) will burn out due to overheating to protect the circuit.
2. Film fuse resistor Film fuse resistor is the most commonly used fuse resistor at present. It is divided into carbon film fuse resistor, metal film fuse resistor and metal oxide film fuse resistor.
