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Among them, the winding resistance is a common high-power resistance, which is made of resistance wire wound on a ceramic insulating skeleton, and the power of a single resistance can reach more than 3KW.
High-power resistors in thick-film technology mainly refer to planar power resistors, which are made of thick-film resistor pastes printed on aluminum oxide and aluminum nitride substrates. The high-power temperature sensor is a solid ceramic resistor. Although this resistor is less well-known than the previous two resistor technologies, it has very significant advantages:
(1) High reliability. The energy absorption and the absorption of instantaneous high-energy pulses of the ceramic body are the strongest.
(2) It is chemically inert and thermally stable. With small and consistent size, it can withstand higher power density and energy.
(3) With completely non-inductive design, it can be applied to the absorption and release of high-frequency high-energy pulses. Its production technology is completely different from that of coil resistors and planar output resistors. Ceramic resistors generally use fired alumina, clay, graphite or silicon, and are uniformly mixed in the form of particles with a certain mass ratio. It is made after passing processes including molding, high temperature sintering, electrode treatment, and packaging testing.
In practical applications, many people worry that failure will occur in the case of poor high-power temperature sensors and severe overload, which will affect the overall normal operation.
The reasons of faults of coil resistance are that the resistance wire is burnt, the resistance is cut off, and the resistance film of the thick film resistor evaporates, which may cause a sharp change in the resistance value, which is irreversible. In this regard, I have compiled 3 common faults about high-power temperature sensors and their solutions.
(1). Why does the high-power temperature sensor have an open flame phenomenon?
The resistance surface of the high-power temperature sensor is coated with a layer of green insulating paint, which will emit smoke and burn at high temperature. When the insulating paint is burned out, there will be no open flame on the surface of the resistor.
(2). Why does the resistance value of the high-power temperature sensor decrease first and then increase?
Reasons for the reduction of overload resistance at initial power:
The resistance of ceramic resistors mainly depends on the contact resistance between graphite particles and the resistance of graphite itself. The graphite particles are irregularly arranged in the resistor in the crisscross way, which will lead to defects in the resistor during fabrication.
When the initial power is overloaded, the bad contact part of the resistor is optimized, the defect rate of the conductive path and the contact resistance value are reduced, so that the contact state between the graphite particles tends to be stable and the resistance value is reduced.
The ceramic resistors of high-power temperature sensors have a negative temperature coefficient, and the resistance decreases with increasing temperature. Reasons for increased resistance after overloading for a period of time:
After the power supply is overloaded for a period of time, because the ceramic resistor cannot withstand the high temperature caused by the power supply overload, the interior of the resistor expands and cracks, and the graphite part is exposed to the air and oxidized. At the same time, the cross-sectional area of the resistor becomes smaller, resulting in a rapid rise in the resistance value. However, when the resistance rises to a certain value, the thermal power of the resistance is very small, and the resistance tends to stabilize.
Why does the ceramic resistor of certain high-power temperature sensor have no open flame, and the whole process will not burn out?
The ceramic surface of the high-power temperature sensor is coated with a high-temperature resistant glaze, which is moisture-proof and can be used for oil immersion. At the same time, the glaze will not burn at high temperatures.