THERMISTORS|Construction|Working|Pros|Cons|Application of Resistive Transducers|Classification|S&T

Introduction to Thermistors

Overview of Thermistors

• The session introduces thermistors as a type of resistive transducer, emphasizing their dependence on temperature for resistance.

• Thermistors can be represented using specific symbols according to international and American standards.

• They require an external power supply for operation, classifying them as passive components with resistance as the primary sensing parameter.

Types and Materials

• Thermistors are made from conducting and semiconducting materials such as manganese, nickel, cobalt, copper ion, and uranium.

• There are two main types: Negative Temperature Coefficient (NTC) thermistors, which are more commonly used due to their inverse relationship between temperature and resistance.

Applications of Thermistors

Key Applications

• Main applications include temperature measurement and control in air conditioning units.

• Other uses involve measuring power at high frequencies, water flow levels, thermal conductivity, and current limiting functions.

Features of Thermistors

• Salient features include compact size, rugged construction, cost-effectiveness, and stability across various temperatures.

Advantages and Disadvantages

Pros of Using Thermistors

• Advantages include accuracy in measurements, durability with a long lifespan, sensitivity to changes in temperature, affordability, and robustness.

Cons of Using Thermistors

• Drawbacks consist of poor performance in extreme temperatures outside specified ranges.

• The output curve can be non-linear or complex under certain conditions.

Characteristics & Classification

Understanding NTC Characteristics

• NTC thermistor characteristics show that resistance decreases as temperature increases; this is fundamental to their function as transducers.

Mathematical Representation

• The equation representing NTC thermistor behavior is R_t = R_0 times e^beta(1/T - 1/T_0) , where R_t , R_0 , T , T_0 , and β represent specific values related to resistance and temperature.

Classification Summary

Understanding Thermistors: NTC and PTC Characteristics

NTC Thermistors (Negative Temperature Coefficient)

• NTC thermistors exhibit an inverse relationship between temperature and resistance; as temperature increases, resistance decreases. This characteristic is crucial for various applications in electronics.

• While NTC thermistors are commonly used, the positive temperature coefficient (PTC) thermistors have a direct relationship where both temperature and resistance increase together. PTC thermistors are less common but serve specific protective functions.

PTC Thermistors (Positive Temperature Coefficient)

• PTC thermistors can be utilized as fuses due to their directly proportional relationship between temperature and resistance, making them suitable for circuit protection by limiting current flow.

• Although PTC thermistors act as current-limiting devices, their application is restricted due to certain constraints that must be considered when integrating them into circuits.

Conclusion