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Thursday, March 7, 2013

Electrical Resistivity Vs Coefficient of Temperature


If the temperature begins to change, the value of resistance for all kinds of resistors also exhibits an adjustment. On the basis that the R-value returns to normal when the temperature is normal, this informative article aims at only on the temporary adjustments that occur if temperature changes. Temperature has two consequences on the level of resistance. The actual size of the resistive material alters as a result and raises the cross-sectional area as well as the length. The other effect is the alter in the resistivity value of the material and for all the materials which we implement for making resistors, the resistivity change is so much more than the changes as a result of change in the proportions that we may concentrate on this alteration alone.

The property of materials that is used to look at the effect of temperature changes is known as the coefficient of temperature, and strictly speaking the coefficient that we make use of is the temperature coefficient of resistance or TCR. The definition is the fractional difference in amount of resistance per degree Celsius. A positive result is observed with the TCR when the temperature increase leads to the resistance increase and a negative result is affected by the TCR when the temperature lowers. While in most cases a low temperature coefficient is needed to keep comparatively persistent values of resistance. Many resistors yet are specifically designed to guarantee a larger resistor temperature coefficient. These types of resistors are known as thermistors and could be useful for temperature measuring or over-current protection. Metal oxide semiconductors are normally used for these thermistors. However there are also silicon based thermistors, these show a more linear response.

Generally, good conductors for instance metals always have a positive temperature coefficient (P T C), but semiconductor materials usually have a negative coefficient, and carbon resistors might have a NTC as well. Furthermore there are thermistors which have a very high TCR (either positive or negative). To show temperature coefficients in a way which are easily accessible or memorable, it is common to quote temperature coefficients in parts as per million per degree. For example, we write the value as 250 ppm/°C rather than 0.00025/°C when we talk about the resistor with regards to being temperature coefficient of the resistor, because this is a form that is more compact and can be remembered effortlessly when making use of statistics.

Much more information on the temperature coefficient of resistors can be found at:

http://www.resistorguide.com/temperature-coefficient-of-resistance/