Negative Temperature Coefficient Of Resistance

The temperature coefficient of resistance is commonly described as even the change in material’s electrical resistance as temperature changes by one degree.

So, when we look at the electrical resistance of conductors like gold, aluminium, silver, and copper, it all comes down to the process of electron collision within the substance. When the temperature rises, the process of electron collision accelerates. As a result, as the conductor’s temperature increases, so will its resistance.

Temperature Coefficient of Resistance

There are two basic reasons why material resistance varies with temperature.

One effect is caused by the number of collisions between charged particles and ions in the substance. Because the frequency of collisions rises with temperature, it is reasonable to expect a small boost in resistance with temp.

This may not always be the case because a few materials have a negative resistance value. This may be explained by the fact that more charge carriers are discharged when the temperature rises, resulting in a drop in resistivity with temperature. This phenomenon is common in semiconductor materials, as one might assume.

When examining the temperature dependence of resistance, it is commonly believed that the temperature coefficient of resistance maintains a linear law. This is true at room temperature and for metals and several other things. However, it has been observed that the resistant effects caused by the number of encounters are not necessarily constant, especially for these materials at extremely low temperatures.

It has been demonstrated that resistivity is inversely related to the mean free route between collisions, resulting in rising resistance with rising temperature. For temperatures above about 15°K, this would be limited by mechanical vibrations of the atoms, resulting in the characteristic linear area. Impurities restrict resistivity below this temperature.

The resistance of a conductor at any given temperature may be determined using the temp, its temperature correlation of resistance, its resistance at a reference temperature, and the temperature of operation. In general, the resistance temperature dependence formula is as follows:

R = R’(1+a(T-T’))

where,

R = resistance at T

R’= resistance at T’

T = material temperature

T’= reference temperature

a = temperature coefficient for resistance 

Negative Temperature Coefficient

Materials with a negative temperature coefficient reduce electrical resistance as their temperature rises. Materials with engineering use often exhibit a quicker decline with temperature, namely the lower coefficient. The smaller the coefficient, the more significant the decrease in electrical resistance with increasing temperature. NTC materials are utilised to manufacture inrush current limiters (because of their greater beginning resistance until the current limiter achieves quiescent temperature), temperature sensors, and thermistors.

A semiconductor’s negative temperature coefficient 

The concentration of charge-carriers increases as the temperature of a semiconducting material rises. As a result, more charge carriers are accessible for recombination, boosting the semiconductor’s conductivity. Because conductivity increases with temperature, the resistivity of the semiconductor material decreases, resulting in a negative temperature coefficient.

Negative Temperature Coefficient Thermistor

NTC thermistors, or negative temperature coefficient thermistors, diminish or increase their resistive value as the working temperature around them rises. NTC thermistors are the most often utilised temperature sensor because they may be employed in almost any equipment where the temperature is a factor.

The electrical resistance against temperature (R/T) relationship of NTC temperature thermistors is negative. Because of an NTC thermistor’s comparatively adverse solid reaction, even minor temperature changes can produce considerable changes in electrical resistance. As a result, they are suitable for precise temperature measurement and management.

A thermistor is an electrical component whose resistance is strongly dependent on temperature; consequently, bypassing a continuous current through it and measuring the potential difference, we can calculate its resistance at a given temperature.

The “B” value of a thermistor seems to be another significant property. The B factor is a material constant dictated by the ceramic material used to make it. It represents the resistive (R/T) curve variance between two temperature points over a specific temperature range. Each thermistor material has a unique material constant and an outstanding resistance vs temperature curve.

Benefits

NTC Thermistors are chosen for thermal imaging applications because of the following benefits:

• High precision
• Rapid reaction
• Low price
• Simple to set up and utilise
• Highly sensitive, making it ideal for applications requiring a narrow temperature range.
• With its two-wire connecting mechanism, they are compatible with a wide range of devices.

Uses

Characteristics of Resistance Time

Temperature sensors, control, and compensation are examples of resistance-temperature characteristics. These also include circumstances in which an NTC thermistor is utilised to link the temperature of the NTC temp sensor to another physical phenomenon.

Characteristics of The Current Time

Time delay, inrush-current limitation, surge suppression, and other operations based on current-time characteristics are only a few examples. These properties are connected to the NTC thermistor’s thermal inertia and dissipation constant.

Voltage-Current Relationship

Applications based on a thermistor’s voltage-current characteristic often require changes in environmental conditions or circuit alterations that require changes in the operating point on a particular curve in the circuit. Depending on the application, this could be used for supply limiting, temperature compensation, or temperature readings.

Conclusion

NTC thermistors seem to be the most often used (particularly the 10K NTC thermistors), and RS could be utilised as an element of a simple voltage – divider circuit with an adding series resistor. Thus, variations in resistance caused by temperature changes result in temperature-related output power. This was all about the NTC Thermistors. Hope this article helps you!