What are metal oxide film resistors? Metal-oxide film resistors are fixed form, axial resistors. They are made of ceramic rod that is coated with a thin film of metal oxides, such as tin oxide. Metal oxide film resistors must not be confused with metal oxide varistors, made of zinc oxide or silicon carbide. Properties Metal oxide film resistors exceed the performance of metal film and carbon film for the following properties: power rating, voltage rating, overload capabilities, surges and high temperatures. Designers choose often the metal oxide film resistor for high endurance applications. For an overview of resistor types with their properties, look here. Stability properties are less good than for the metal film resistor. The metal oxide film resistors have poor properties for low values and tolerance. The temperature coefficient is around 300 ppm/°C, which is higher than for metal film types. The resistance material for metal oxide resistors is tin oxide that is contaminated with antimony oxide, this is to increase the resistivity. Metal oxide resistors can withstand higher temperatures than carbon or metal film resistors. The noise properties are similar to carbon resistors. Maximum operating temperature comparison Material Carbon film Metal film Metal oxide Temperature 200 °C / 390 °F 250-300 °C / 480-570 °F 450 °C / 840 °F [embedit snippet="adsense"] Typical Applications Many properties of metal oxide film resistors are similar to metal film resistors. For basic use, metal film and metal oxide film are currently the predominant resistor types. Compared to carbon film, the prices are just as low. Only for dissipation values above 1 watt combined with reasonable stability, the carbon film resistors are still more cost efficient. Construction The metal oxide film is mostly produced with chemical deposition methods. Almost always a ceramic carrier is used as substrate. The deposition process involves...
Resistors are produced with a wide variety of materials and manufacturing processes. Each resistor material has its typical properties and specific areas of use. The main types that are used in electrical engineering are summed below. Wirewound (WW) These types are made by winding resistance wire in a spiral around a non-conductive core. The resistance wire is usually a nickel-chromium alloy and the core is often ceramic or fiberglass. A coating such as vitreous enamel is used for protection. The spiral winding has capacitive and inductive effects that makes it not suitable for applications higher than 50 kHz. Often other winding techniques are used to reduce the undesired high frequency effects. Wirewound resistors are essentially produced for high precision or for high power applications. They have low noise, are robust, and are temperature stable. Resistance values are available from 0.1 up to 100 kW, with accuracies between 0.001 and 20%. Carbon Composition (CCR) The resistive element is made from a mixture of fine carbon particles and a non-conductive ceramic material. The substance is pressed in a cylindrical shape and baked. The resistance value depends on the dimensions of the body and the ratio between carbon and ceramic material. More carbon means a lower resistance. Carbon composition resistors are remarkably reliable, but have a poor accuracy with a maximum tolerance around 5%. Until the 1960s they were the standard for general applications. They quickly lost market share as other resistor types came on the market with better properties for tolerance, voltage coefficient, temperature coefficient, stability and finally cost. However, their ability to withstand high energy pulses and their high reliability makes them still useful for certain applications. Examples are power supplies and welding controls. Carbon Film A thin, pure carbon film is deposited on an insulating cylindrical...