Positive temperature coefficient applications

Platinum is especially suitable for this application because even at high temperatures it has a good stability and a good resistance to contamination. However, different metals, all having a positive temperature coefficient, may be used, such as tungsten (for very high-temperature applications), nickel and nickel alloys and also (but rarely because of their low resistivity) gold and silver. 

Figure 6.45 Schematic illustration of negative temperature coefficient (NTC) and positive temperature coefficient (PTC) effects. Reprinted, by permission, from D. M. Moffatt, J. Runt, W. Huebner, S. Yoshikawa, and R. Nenham, in Composite Applications, T. L. Vigo and B. J. Kinzig, eds., p. 52. Copyright 1992 by VCH Publishing, Inc.

In many applications, temperatures of stator windings and bearings of motors are continuously monitored during operation by Pt-100 resistance thermometers or PTC (positive temperature coefficient) temperature sensors. 

Crytal chemitry. The effect of solid solution on the transition behavior of perovskite (ABX3) structures has been intensively scrutinized for more than 50 years. These materials have merited continuous attention because of their enormous technological versatility. As multilayer capacitors, piezoelectric transducers, and positive temperature coefficient (PTC) thermistors they generate a market of over 3 billion every year (Newnham 1989, 1997). In addition to ease of fabrication, these compounds exhibit a number of attributes required of ideal actuators (1) They display very large field-induced strains (2) They offer quick response times and (3) Their strain-field hysteresis can be chemically controlled to be very large or negligibly small, depending on the application. Details of their technical applications can be found in Jaffe et al. (1971) and Cross (1993). 

These standards have been widely used by the Li-ion battery manufacturers and users to evaluate the battery safety characteristics to ensure battery safety in applications. Various safety devices including thermal control devices such as the positive temperature coefficient switches and electronic control devices such as various IC protection circuits have been successfully used for Li-ion batteries and battery packs. With an adequate combination of various safety devices, one can protect a Li-ion battery from overcharge, overdischarge, hard short circuit, impact, and other safety concerns throughout its applications. 

One another major application in this field is the use of Y and La as doping agents for BaTiOs - the main component, which preserves the positive temperature coefficient of thermistors. 

Conducting polymer composite materials are becoming common in many applications such as electrodes, conductive coatings and adhesives, positive temperature coefficient materials, and heaters. 

Positive-temperature-coefficient (PTC) devices that, at normal currents and temperatures, have a very low value of resistance. When excessive currents pass through these devices or the battery temperature increases, the resistance increases orders of magnitude, limiting the current. These devices are incorporated internally in some cells by the cell manufacturer. When using cells with internal protection, it is advisable to use an external PTC selected to accommodate both the current and the voltage levels of the battery application (see Sec. 5.5.1). 

Sauer, H. A. and S. S. Flaschen Positive Temperature Coefficient of Resistance Thermistor Materials for Electronic Applications, Proc. 1956 Elec. Comput. Conf., pp. 41 6, 1956. 

The specific conductivity of a large number of oxide melts is in excess of 1 ohm-1 cm-1 and the temperature coefficient of conductance is positive. Two types of experiments from which conclusions are drawn regarding the mechanism of conduction are to be found in the literature. In one, the applicability of Faraday s laws is directly tested. In the second case, the conductivity of both the crystalline solid up to the melting point and that of the melt is measured if the change in specific conductivity on fusion is negligible, and if the so-called activation energy EK defined by... 

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. 

The application of permanent magnets in measuring devices or in devices in aircraft or space systems requires a small temperature coefficient (TC) of Bf. The combination of CosSm which has a negative TC, with CosGd, which has a positive TC, yields magnets with reduced temperature dependence of B, reaching about... 

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