Positive-temperature coefficient resistor

While ZnO is outstanding for the high a values that can be attained, other systems that contain barrier layers, for instance the positive temperature coefficient resistors based on BaTiC>3, also show the effect, but alternatives to ZnO have not been developed commercially. 

Conductive polymer material used for the positive temperature coefficient resistor (PTC) overcurrent protection device Activated carbon cathode and anode... 

Perovskite-type titanates (e.g. SrTiCL, BaTiOi) constitute an important class of electroceramic materials and are, for example, used in PTC (positive temperature coefficient) resistors, capacitors, varistors or sensors [324-326]. A degradation process that... 

Positive temperature coefficient resistors are charac-terizedbyaresistancethatisonlymoderately dependent on temperature below a certain temperature, but increases very strongly above that temperature. 

Meyer J (1974) Stability of polymer composites as positive-temperature-coefficient resistors, Polym Eng Set 14 706-716. 

Donor-doped BaTi03 is the basis of positive temperature coefficient (PTC) resistors (see Section 4.4.2). The insulating dielectrics formed with high donor concentrations have a low oxygen vacancy content and are therefore less prone to ageing and degradation. 

Resistive materials used in thermometry include platinum, copper, nickel, rhodium-iron, and certain semiconductors known as thermistors. Sensors made from platinum wires are called platinum resistance thermometers (PRTs) and, though expensive, are widely used. They have excellent stability and the potential for high-precision measurement. The temperature range of operation is from -260 to 1000°C. Other resistance thermometers are less expensive than PRTs and are useful in certain situations. Copper has a fairly linear resistance-temperature relationship, but its upper temperature limit is only about 150°C, and because of its low resistance, special measurements may be required. Nickel has an upper temperature limit of about 300°C, but it oxidizes easily at high temperature and is quite nonlinear. Rhodium-iron resistors are used in cryogenic temperature measurements below the range of platinum resistors [11]. Generally, these materials (except thermistors) have a positive temperature coefficient of resistance—the resistance increases with temperature. 

Thermistors are resistors with a temperature-dependent value of their resistance. There are three types of thermistors CTT (critical temperature thermistors), NTC (negative temperature coefficient), and PTC (positive temperature coefficient) thermistors. Their thermal behavior is shown in Figure 9.7. 

Negative temperature coefficient (NTC) resistors for example, spinel structure oxides, manganese(ll. 111) oxide - Mn304 Positive temperature coefficient (PTC) resistors for example, aluminum oxide AI2O3, magnesium oxide - MgO... 

Ordinary carbon and pure polycrystalline graphite having small crystallites have negative temperature coefficients of resistance (semiconductor), while single crystals or graphite have positive temperature coefficients. The resistance-temperature relations for ordinary carbon resistors widely used in radio circuitry are of particular interest in low-temperature work because of their usefulness as sensitive thermometers and liquid level sensing devices. 

There are numerous uses for resistors with high values of the temperature coefficient of resistance (TCR) and they may be negative (NTC) or positive (PTC). An obvious application is in temperature indicators that use negligible power to monitor resistance changes. Compensation for the variation of the properties of other components with temperature may sometimes be possible in this case the applied power may be appreciable and the resulting effect on the temperature-sensitive resistor (TSR) must be taken into account. 

Positive temperatnre coefficient (PTC) resistor operates by a phase change in the conductive polymer placed internally to terminal connection which increases its resistance to minimize cnrrent flow to the cell terminals when either the current flow exceeds the design point or the cell internal temperature exceeds the set point. 

Thermistors are semiconductor resistors that have resistor values that vary over a wide range. They are available with both positive and negative temperature coefficients and are used for temperature measurements and control systems, as well as for temperature compensation. In the latter they are utilized to offset unwanted increases or decreases in resistance due to temperature change. 

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