The Construction and Features of Metal Film Resistors

2018-06-08 19:30:24 post by microhm

In resistor industry, RJ refer to metal film resistor which is usually a cylindrical axial resistor ones. Other film type resistors are carbon film, thick and thin film resistors. The resistor value is marked by color code bands or with text. The Temperature Coefficient of Resistance is usually between 50 and 100 ppm/K.The metal film resistors are available with tolerances of 0.1, 0.25, 0.5, 1 and 2%.

Metal film resistors have good characteristics for tolerance, stability and TCR. What's more, the resistors feature low noise properties and a high linearity because of a low voltage coefficient. Therefore they are often used in active filters, bridge circuits, household electrical appliances, communications, instruments and meters. The appearance of metal film resistors is similar to carbon film resistors, but their properties for stability, accuracy and reliability are considerably better. Wirewound or carbon composition resistors are easier damaged by voltage surges and power overloads.

Metal film resistors have so many merits, how are they constructed? let's figure out.

metal film resistor.jpg

Metal film resistors are axial resistors with a thin metal film as resistive element. The thin film is deposited on usually a ceramic body.The resistance material is often nickel chromium (NiCr).For better accuracy, the deposited metal is artificially aged by keeping it for a long period at a low temperature. The stability and resistance of metal film resistors are strongly dependent on the thickness of the metal film (50-250 nm). A larger thickness of the layer results in a lower resistance value and a better stability. A metal cover is pressed on both ends with the connection leads.  Then the intended resistance is achieved by cutting a spiral shaped slot in the thin metal layer by lasers. The resistor is covered with several coating layers that are baked individually. The coating protects against moisture, mechanical stresses and has a higher dielectric strength. 

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TAG:   metal film resistors thin and thick film resistors