Other variable resistors, including rheostats and potentiometers

85.33 Electrical resistors (including rheostats and potentiometers), other than heating resistors. 8533.10 - Fixed carbon resistors, composition or film types - Other fixed resistors : 8533.2 1 8533.29 - - For a power handling capacity not exceeding 20 W - - Other - Wirewound variable resistors, including rheostats and potentiometers : 8533.31 8533.39 8533.40 8533.90 - - For a power handling capacity not exceeding 20 W - - Other - Other variable resistors, including rheostats and potentiometers - Parts (A) Resistors (resistances). These are conductors whose function is to provide a given electrical resistance in a circuit (e. .,to limit the current flowing). They vary greatly in size and shape, and in the materials o which the are made. They ma be made of metals in the form of bars, shapes or wire, often coiledYn bobbins) or of car on in the form of ro s, or of carbon, silicon carbide, metal or metal oxide film. They may be obtained in the form of individual corn onents by a printing process. Certain resistors may be fitted with a number of termina s allowing the whole or part to be included in the circuit. d % P The heading includes : (1) Oil immersed resistors. (2) Carbon resistance lamps, in the form of an electric light bulb but with a s ecial carbon filament; however, carbon filament lamps for lighting purposes are exc uded (heading 85.39). I' (3) Barretters consisting of iron filaments assembled in a glass tube filled with hydro en or helium; these have the property of varying automatically within certain limits anC f so keeping the current constant. (4) Standard resistors used for comparison and measuring purposes (e.g., in laboratories); also resistance boxes consisting of a number of such resistors assembled in a box with switching or terminal arrangements for connecting any required combinations of the resistors into the circuit. (5) Non-linear resistors : de ending on temperature (thermistors) with a negative or positive temperature coe icient (usually mounted in glass tubes), and non-linear resistors depending on voltage (varistorsNDR), but not including varistor diodes of heading 85.41. # (6) Resistors known as "strain gauges "being the sensitive elements of a strain measuring instrument. The heading excludes : (a) Heating resistors (heading 85.16 or 85.45). @) Light dependent resistors (heading 85.41). (B) Rheostats. These are variable resistors with a slidin contact or other means enabling the f value of resistance in the circuit to be varied at will. hey include, slide wire rheostats with a cursor sliding over a resistance coil; step-by-step rheostats; hydro-rheostats with movable electrodes immersed in a liquid conductor; automatic rheostats (e. with minimum or maximum current or voltage operating mechanisms); and centrifugal r eostats. k (e.g., theatre dimmers used in a Certain rheostats are designed for and motor starters and controllers lighting circuit to extin sh the consishng of a number o resistors switching arrangement for switchin in or out one or more resistors in the motor circuit). Nevertheless, they remain classifie here. Fl f (C) Potentiometers. These consist of a fixed resistor between two contacts and a sliding tapping whch can make contact on any point of the resistor. PARTS Sub'ect to the general provisions regarding the classification of parts (see the General Exp anatory Note to Section XVI), parts of the resistors of this heading are also classified here. I