SENSORS


This Blog is made so that the students and engineers get the basic knowledge on the various types of sensor technologies available. This blog contains information on the working of various kinds of sensors, their advantages, disadvantages, common applications and links of best manufacturers.

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How Thermistor works

The Thermally sensitive resistors(Thermistors) are similar to RTD's and are electrical resistors whose resistance changes with temperature. Thermistors are made of semiconductor material. There are 2 types of thermistors, The PTC and the NTC.
The resistance of the PTC(positive thermal coefficient) increases with increasing temperature. The resistance of the NTC(negative thermal coefficient) decreases with increasing temperature. The NTC is the most common among the two types of thermistors.
The Linear relationship between the resistance and temperature is (dR)=k(dT)
where (dR)=change in resistance, (dT)=change in temperature, k=coefficient of resistance. For PTC k is positive and for NTC k is negative.

The Advantages of thermistors are
•The thermistors are more sensitive than the RTD's and thermocouples
•The thermistors have quick response time

The Disadvantages of thermistors are
•Linearity of a thermistor is not good
•Since they are made of semiconductor, thermistors are susceptible to permanent decalibration at high temperatures than are RTD's or the thermocouples.

Some of the applications of thermistors are
•Thermistors are widely used in applications as temperature sensors and as current limiters. A PTC is used as a current limiter. As the current increases the temperature increases. hence the resistance increases limiting the current.

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