Resistor

The main polymer use in chip resistors relates to the encapsulation material which is frequently PA but may be Novolac epoxy or epoxy resin. Silicone rubber encapsulation, which provides a cushioning layer which isolates the resistive element from external stresses, and polymerised moisture protection layers are two other uses of polymers in resistors. Encapsulated resistor capacitor networks utilise epoxy/anhydride conformal body material. Conformal implies a coating of uniform thickness as would be obtained by a dipping process, for example. 

Small wirewound resistors are made by winding the resistance wire round a proprietary bobbin and then encapsulating it in silicone rubber over which an epoxy shell is moulded. Other resistor formats use foil elements with Kapton/adhesive insulation coated with epoxy enamel. 

Plastic potentiomers described as robust yet economical use a conductive polymer as the resistive element of the design. The polymer used is effectively a thick screen-printed film ink similar to the cermet (ceramic/metal) compounds which are also used in variable resistors. Conductive polymers are superior to cermet in terms of their dynamic noise characteristic but have inferior moisture resistance, temperature coefficients, power dissipation and wiper current capacities. The temperature coefficient and power handling capabilities of wirewound resistors are higher. 

The shaft of a variable resistor will often be made from a thermoplastic polymer whilst the mounting bush may be glass-filled Nylon or a diecast zinc alloy. 

PTC devices are available in a range of specifications to meet defined requirements in low voltage electronic circuits where they may, for example, protect automotive electronic circuits, cellular phones, laptop computers, loud speakers, power transformers, rechargeable battery packs, security and fire alarm systems and other products. 

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M.p. 296 C. Accepts an electron from suitable donors forming a radical anion. Used for colorimetric determination of free radical precursors, replacement of Mn02 in aluminium solid electrolytic capacitors, construction of heat-sensitive resistors and ion-specific electrodes and for inducing radical polymerizations. The charge transfer complexes it forms with certain donors behave electrically like metals with anisotropic conductivity. Like tetracyanoethylene it belongs to a class of compounds called rr-acids. tetracyclines An important group of antibiotics isolated from Streptomyces spp., having structures based on a naphthacene skeleton. Tetracycline, the parent compound, has the structure ... 

Two difierent components contribute to impedance the resistive or real component due to resistors and the reactive or imaginary component from AC circuitry elements, such as capacitors, inductors, etc. Unlike the resistive component, the reactive impedance affects not only the magnitude of the AC wave but also its time-... 

Figure C2.13.3. Schematic illustrations of various electric discharges (a) DC-glow discharge, R denotes a resistor (b) capacitively coupled RF discharge, MN denotes a matching network (c), (d) inductively coupled RF discharge, MN denotes matching network (e) dielectric barrier discharge.

W = working electrode SW = slide-wire resistor T = tap key i = galvanometer. 

R = resistor i = gaivanometer A = auxiiiary eiectrode W = working eiectrode ... 

The Maxwell and Voigt models of the last two sections have been investigated in all sorts of combinations. For our purposes, it is sufficient that they provide us with a way of thinking about relaxation and creep experiments. Probably one of the reasons that the various combinations of springs and dash-pots have been so popular as a way of representing viscoelastic phenomena is the fact that simple and direct comparison is possible between mechanical and electrical networks, as shown in Table 3.3. In this parallel, the compliance of a spring is equivalent to the capacitance of a condenser and the viscosity of a dashpot is equivalent to the resistance of a resistor. The analogy is complete... 

In another type of measurement, the parallel between mechanical and electrical networks can be exploited by using variable capacitors and resistors to balance the impedance of the transducer circuit. These electrical measurements readily lend themselves to computer interfacing for data acquisition and analysis. 

Electricity generation Electric lighting Electric melting Electric power Electric resistor furnaces Electric vehicles... 

Several kinds of conduction mechanisms are operative in ceramic thermistors, resistors, varistors, and chemical sensors. Negative temperature coefficient (NTC) thermistors make use of the semiconducting properties of heavily doped transition metal oxides such as n-ty e Ti O andp-ty e... 

NL Li O. Thick film resistors are also made from transition-metal oxide soHd solutions. Glass-bonded Bi... 

Equally important as tape casting in the fabrication of multilayer ceramics is thick film processing. Thick film technology is widely used in microelectronics for resistor networks, hybrid integrated circuitry, and discrete components, such as capacitors and inductors along with metallization of MLC capacitors and packages as mentioned above. 

Fig. 10. Exploded view of a monolithic multicomponent ceramic substrate. Layers (a) signal distribution (b) resistor (c) capacitor (d) circuit protection ...

H. T. Sa whill and co-workers, "Low Temperature Co-Firable Ceramics with Co-Fired Resistors," International Society of Hybrid Microelectronics Proceedings, 1986, pp. 473—480. 

Relatively smaller amounts of very high purity A1F. are used ia ultra low loss optical fiber—duotide glass compositions, the most common of which is ZBLAN containing tirconium, barium, lanthanum, aluminum, and sodium (see Fiber optics). High purity A1F. is also used ia the manufacture of aluminum siUcate fiber and ia ceramics for electrical resistors (see Ceramics AS electrical materials Refractory fibers). 

Fig. 1. Main types of electric furnaces (a) resistance furnace, indirect heat (resistor furnace) (b) resistance furnace, direct heat (c) arc furnace (d) induction furnace. A, charge to be heated or melted B, refractory furnace lining C, electric power supply D, resistors E, electrodes F, electric arc G,...

A. G. E., Robiette, Electnc Melting Practice, John Wiley Sons, Inc., New York, 1972, 412 pp., arc, induction resistor, and special melting furnaces are discussed. 

The most widely used and best known resistance furnaces are iadirect-heat resistance furnaces or electric resistor furnaces. They are categorized by a combination of four factors batch or continuous protective atmosphere or air atmosphere method of heat transfer and operating temperature. The primary method of heat transfer ia an electric furnace is usually a function of the operating temperature range. The three methods of heat transfer are radiation, convection, and conduction. Radiation and convection apply to all of the furnaces described. Conductive heat transfer is limited to special types of furnaces. 

From 760 to 960°C, circulating fans, normally without baffles, are used to improve temperature uniformity and overall heat transfer by adding some convection heat transfer. They create a directional movement of the air or atmosphere but not the positive flow past the heating elements to the work as in a convection furnace. Heating elements ate commonly chrome—nickel alloys in the forms described previously. Sheathed elements are limited to the very low end of the temperature range, whereas at the upper end silicon carbide resistors may be used. In this temperature range the selection of heating element materials, based on the combination of temperature and atmosphere, becomes critical (1). 

Chrome—nickel alloy heating elements that commonly ate used in low temperature furnaces are not suitable above the very low end of the range. Elements commonly used as resistors are either silicon carbide, carbon, or high temperature metals, eg, molybdenum and tungsten. The latter impose stringent limitations on the atmosphere that must be maintained around the heating elements to prevent rapid element failure (3), or the furnace should be designed to allow easy, periodic replacement. 

Conduction furnaces utilize a Hquid at the operating temperature to transfer the heat from the heating elements to the work being processed. Some furnaces have a pot filled with a low melting metal, eg, lead, or a salt mixture, eg, sodium chloride and potassium chloride, with a radiation-type furnace surrounding the pot. Although final heat transfer to the work is by conduction from the hot lead or salt to the work, the initial transfer of heat from the resistors to the pot is by radiation. 

There are large-scale operations using direct-heat resistance furnaces. These are mainly in melting bulk materials where the Hquid material serves as a uniform resistor. The material is contained in a cmcible of fixed dimensions which, coupled with a given resistivity of the material, fixes the total resistance within reasonable limits. The most common appHcation for this type of direct-heat electric resistance furnace is the melting of glass (qv) and arc furnaces for the melting of steel (qv). 

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