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Resistors
Published in Kevin Robinson, Practical Audio Electronics, 2020
One last component characteristic worth mentioning briefly is the temperature coefficient. A resistor’s temperature coefficient indicates how its value changes as its temperature changes. A typical temperature coefficient may be quoted as ±50ppm/°C, where ppm stands for ‘parts per million’. This value thus indicates that for every °C change in temperature, the resistance may change by up to 50 millionths of the total value, e.g. a nominally 1MΩ resistor might change in value by up to ±50Ω for each °C change in its temperature. Typically with resistors as the temperature goes up the resistance goes up, and as the temperature goes down the resistance goes down. This is called a positive temperature coefficient. There are also components which exhibit a negative temperature coefficient (as temperature goes up, resistance goes down, and vice versa). Both these property are sometimes used to good effect in specialised components, but on the whole, for standard resistors, the smaller the temperature coefficient the better. Ideally the resistance should not change at all as the temperature changes, but in reality it will always vary to some extent.
Resistance variation
Published in John Bird, Science and Mathematics for Engineering, 2019
The temperature coefficient of resistance of a material is the increase in the resistance of a 1Ω resistor of that material when it is subjected to a rise of temperature of 1°C. The symbol used for the temperature coefficient of resistance is α (Greek alpha). Thus, if some copper wire of resistance 1Ω is heated through 1°C and its resistance is then measured as 1.0043Ω then α = 0.0043Ω/Ω°C for copper. The units are usually expressed only as ‘per °C’, i.e. α = 0.0043/°C for copper.
Enzyme Thermistor Devices
Published in Loïc J. Blum, Pierre R. Coulet, Biosensor Principles and Applications, 2019
In this type of instrumentation thermistors are normally used as temperature transducers. Thermistors are resistors with a very high negative temperature coefficient of resistance. They are ceramic semiconductors made by sintering mixtures of metal oxides, such as manganese, nickel, cobalt, copper, iron, and uranium. They can be obtained in many different configurations, sizes (down to 0.1–0.3 mm beads), and resistance values from such manufacturers, as Fenwal Electronics (Framingham, MA), Victory Engineering Co. (Springfield, NJ), and Siemens AG (Munich, West Germany). The hitherto best empirical expression to describe the resistance-temperature relationship is the Steinhart-Hart equation: () 1T=A+B(lnR)+C(lnR)3
Dynamic thermoviscoelastic thermistor problem with contact and nonmonotone friction
Published in Applicable Analysis, 2018
Krzysztof Bartosz, Tomasz Janiczko, Paweł Szafraniec, Meir Shillor
The original model describes the combined effects of heat conduction, electrical current and Joule’s heat generation in a device made of a material that has strong temperature-dependent electrical conductivity. There are Positive and Negative Temperature Coefficient thermistors, usually denoted by PTC and NTC, respectively; in the former the electrical conductivity decreases with increasing temperature whereas in the latter it increases with the temperature. PTC thermistors may be used in switches or electric surge protection devices, among other applications. A PTC electric surge device operates as follows: when there is a sudden current increase in the circuit the device heats up, which leads to a sharp drop in its electrical conductivity, thus shutting down the circuit. Once the surge is over the device cools down, its conductivity increases and the circuit again becomes fully operational. However, it was found that the sudden temperature increase may cause high thermal stresses that affect the integrity of the device ([9,11]) causing the appearance of cracks and device failure. The electro-thermoelastic aspects of the thermistor were studied in [16] where the model was set as a fully coupled system of equations for the temperature, electrical potential and (visco)elastic displacements. The material constitutive behavior was assumed to be linear since the nonlinearities in the system resided in the electrical conductivity, the Joule heatings and the viscous heating terms. The existence of a weak solution for the problem was established using regularization, time-retarding, and a convergences argument.
Serially connected tantalum and amorphous indium tin oxide for sensing the temperature increase in IGZO thin-film transistor backplanes
Published in Journal of Information Display, 2023
EunSeong Yu, SeoungGyun Kim, SeoJin Kang, HyuckSu Lee, SeungJae Moon, JongMo Lee, SeungBae An, ByungSeong Bae
A temperature sensor using the temperature-dependent resistivity of metal was also reported to monitor the temperature on the display panel. It offers the advantages of low cost, process compatibility with the display backplane, and good stability against bias and light illumination. Lee et al. integrated a metal thermal sensor into an LCD without any change in the process and could measure temperatures from −10 °C to 80 °C [10]. A complicated process is not required for thin-film metal temperature sensors, and they can be made using simple metal materials. The change in resistance with the change in temperature is used to sense temperatures, and a large temperature coefficient provides high sensitivity. The metal film used for temperature sensing was connected to an external reference resistor for the measurements. After a voltage was applied, the temperature-dependent voltage was measured at the connected node. The voltage is determined by the ratio of the sense metal resistance to the resistance of the reference resistor [10], which has the disadvantage of yielding a sensing error when the reference resistance changes owing to environmental temperature variation. Therefore, a low-temperature coefficient resistor was used as the reference resistor. Another way to measure the temperature without the reference resistor is to measure the voltage while forcing a constant current [11]. To overcome this drawback, a metal temperature sensor without an external resistor was proposed, in which two conductors with different temperature coefficients are used for temperature sensing [12]. Temperature-dependent voltages were measured at the junction of the two conductors with a DC voltage applied to both ends of the sensor [12].