Basic knowledge of wound resistor

Wire wound resistance is a kind of fixed resistance. The wire wound resistor is formed by winding the resistance wire on the insulating frame. The resistance wire is generally made of nickel chromium, manganese copper and other alloys with certain resistivity. The insulating skeleton is made of ceramic, plastic, metal coated with insulating layer and other materials in various shapes such as tube shape and flat shape. The resistance wire can be wound in one layer or multiple layers on the skeleton as required, or the non inductive winding method can be adopted. Winding resistance is mainly used for voltage division, voltage reduction, shunt and load resistance in AC and DC circuits such as precision instruments, telecommunication instruments and electronic equipment.

The wound resistor is made of nickel chromium wire, manganese copper wire and constantan copper wire wound on the porcelain tube. It is divided into fixed type and adjustable type. The wound resistor is characterized by high resistance accuracy, low noise during operation, stable and reliable, can withstand high temperature, and can still work normally under the ambient temperature of 170 ℃. However, it is large in size and low in resistance, mostly below 100 kohm. In addition, due to structural reasons, its distributed capacitance and inductance coefficient are relatively large and cannot be used in high-frequency circuits.
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The wire wound resistor is formed by winding the resistance wire on the insulating frame. The resistance wire is generally made of nickel chromium, manganese copper and other alloys with certain resistivity. The insulating skeleton is made of ceramic, plastic, metal coated with insulating layer and other materials in various shapes such as tube shape and flat shape. The resistance wire can be wound in one layer or multiple layers on the skeleton as required, or the non inductive winding method can be adopted.

Wire wound resistance is a kind of fixed resistance. Its circuit symbol is the same as that of ordinary resistor. The internal and external structure of the wire wound resistor is shown in the figure. Its innermost layer is a glass fiber core pillar, on which a resistance wire is wound. The two end wires of the resistor and the lead wire of the solder pin are crimped together internally, and the outer layer is sealed with insulating packing.

Types of wire wound resistors

There are many types of wire wound resistors, which can generally be divided into fixed type and adjustable type.

Commonly used wire wound resistors include: RX20, rx21, rx22 glazed wire wound resistors, rx25 painted wire wound resistors, rx24 power wire wound resistors, rx10, rx12 precision wire wound resistors, rxg5 wire wound porcelain shell resistors, etc.

As the wire wound resistor has the characteristics of high accuracy and good stability, it can be used in the circuits of instruments and meters, such as the voltage divider and shunt circuit of the pointer multimeter, and also can be used in the resistance box circuit. Because it can withstand large power, it is also used as a current limiting resistor in the power supply circuit. However, due to its large inductance, it cannot be used in high-frequency circuits (which may interfere with the circuit).

Working principle of wire wound resistor

The wire wound resistor is a kind of resistor that is wound on the insulation skeleton by the resistance wire and then insulated and packaged. As shown in the figure, the resistance wire is generally made of nickel chromium, manganese copper and other alloys with a certain resistivity. The insulation skeleton is generally made of ceramic, plastic and metal skeleton coated with insulation layer. It has the characteristics of small temperature coefficient and high accuracy. Among the wire wound resistors, there is a high-power wire wound resistor which is made of ceramic as a skeleton and coated with glaze or other heat-resistant and heat dissipation insulating materials on the outer layer of the resistor. The wire wound resistor is characterized by large dissipation power, up to several hundred watts. It is mainly used as a high-power load and can work in the environment of 150 ℃ ~ 300 ℃.

Among the wire wound resistors, there is also an adjustable wire wound resistor, which is equipped with a movable snap ring on the outside of the wire wound as the contact lead end, and a narrow window is left on the glaze (paint) layer to expose the winding contact track. The snap ring can adjust the resistance value by moving the contact on the contact track, so it is a variable resistor. There are two common types of enamelled wire wound resistors and painted wire wound resistors.

Effect of winding resistance

The wire wound resistor is composed of a resistance wire wound on the insulating skeleton, and is generally made of a medium with a certain resistivity, such as nickel chromium, manganese copper and other alloys. The wound resistor is mainly used to play the role of step-down, shunt, load, feedback, energy transfer and matching in the low-frequency AC circuit, or as an absorber and voltage divider in the power supply circuit. It can also be used as a shunt in the oscillation circuit, the attenuation adjustment in the transformer and the pulse forming circuit. In addition, it can also be used for discharge and spark elimination of filter capacitor in rectifier. At the same time, it can be widely used in home appliances, medical equipment, automobile industry, railway, aviation, military equipment and instruments.

Manufacturing process of winding resistor

The manufacturing idea is generally as follows: the winding resistance is to wind the resistance wire on the insulating rod or insulating column in a certain direction, but this single spiral winding resistance will produce inductance effect in the circuit and affect the accuracy. In order to eliminate this effect, the double helix reverse winding method is adopted to make the inductance generated by the two coils cancel each other, and the whole winding resistance presents no or slight inductance to the external circuit, which is called the non inductive winding resistance. The working principle is to make two coils with opposite magnetic field directions cancel each other's inductance, and the external circuit presents the characteristics of no or slight inductance.

How to see the resistance value and power of winding resistance

Connect the resistor and the sliding rheostat in series in the same circuit, measure the current I through the resistor with an ammeter, measure the voltage u at both ends of the resistor with a voltmeter, calculate the resistance value from R = u / I, and calculate the power from P = UI.