1. Chapter 2 Exercise Thermistor  Also called thermal resistor as the resistance varies as a function of temperature.  Manufactured in the form of beads, discs and rods.  Most thermistors have a negative coefficient (NTC) of temperature resistance.  Three important characteristics: o Resistance – Temperature o Voltage – Current o Current – Time

2. Thermistor

4.  Major applications of thermistors are measurement and control of temperature.  Other applications of thermistors: o Measurement of power at high frequencies. o Measurement of thermal conductivity. o Measurement of level, flow and pressure of liquids. o Measurement of composition of gases. Vacuum measurement. Thermistor

5. Advantages o High sensitivity especially in NTC region. o Fast response over narrow temperature range. o Cold junction compensation is not required. o No problems on contact and lead resistance. o Low cost and small size. Limitations o Characteristics of resistance are non- linear. o Not recommended for wide temperature range application. o Need a shielded power lines or filters and low excitation current. Thermistor

6. Thermistor – Exercise Question