What is thermistor

Theory of thermistor:

Michael Faraday, the English scientist first discovered the concept of thermistor in 1833 while reporting on the semiconductor behaviour of silver sulfide. Through his research, he noticed that the silver sulfides resistance decreased as the temperature increased. This discovery would later lead to the commercial production of the thermistors in 1930 when Samuel Ruben invented the first commercial thermistor. Since then technology has improved paving the road to improved manufacturing processes along with the availability of higher quality material.


Definition:

A thermistor is defined as a kind of resistor whose electrical resistance depends on varies with the changes in temperature. A thermistor is a temperature sensitive device. Basically, the thermistor is made of semiconductor materials that mean their resistance lies between the conductor and the insulator.


Thermistor symbol:

The variation in the thermistor resistance shows that either conduction or maybe power dissipation occurs in the thermistor. The circuit diagram of thermistor uses the rectangular block which has a diagonal line on it.
thermistor symbol
Thermistor symbol


Types of  Thermistor:

The thermistor is classified into two types of based on how they behave with the change in temperature

  • Negative temperature coefficient temperature thermistor (NTC)
  • Positive temperature coefficient  temperature thermistor (PTC)
So now let us discuss these two types of the thermistor to better understand this topic:

Negative temperature coefficient thermistor (NTC): 

In this type of thermistor the temperature increases with the decrease of the resistance. The resistance of the negative temperature coefficient thermistor is very large due to which it detects the small variation in the temperature.

Positive temperature coefficient thermistor (PTC): 

The resistance of the thermistor increases with the increases in the temperature. 


Application for NTC and PTC thermistor include:
  • Temperature compensation 
  • Temperature control
  • Temperature measurement
  • Inrush current limiting

Benefits of NTC and PTC thermistors:

NTC thermistor is basically rugged, stable, reliable and equipped more than other types of temperature sensors to handle extreme environmental conditions and noise immunity.
  • Compact size
  • Fast response time
  • Cost efficient
  • This thermistor was the ability to obtain a specific resistance at a particular temperature
Advantages and Disadvantages of thermistor:

Advantages of thermistor:
  • It is a small size
  • Easy to use
  • They are fast in operation
  • It has good sensitivity in NTC region
  • Fast response over the narrow temperature range
  • Cost is low
  • Very responsive to changes in temperature
  • High accurate
  • Repeatable
  • Options for customization
  • Easily interfaced to electronics instrumentation

Disadvantages of thermistor:
  • Thermistor need for shielding power lines
  • Extremely non-linear
  • Passive
  • More fragile as they are semiconductor devices
  • Susceptible to self-heating errors
  • The excitation for large temperature range
For detailed information:
Read  more >> Advantages and disadvantages of a thermistor

You have also read:
Application of Thermistor:
  • It is used in automatic temperature controllers
  • It is widely used in temperature measurement
  • The thermistor measures the thermal conductivity
  • It is also used for biasing and compensating circuit of a transistor
  • In electronics circuit used for the temperature compensation
  • A thermistor is used in the control devices actuated by temperature
  • It is used the measurement of flow
  • It is used for the measurement of high-frequency power
  • It measures the composition of gases
  • It is used to measures the vacuum and provides the time delays
  • The thermistor measures the pressure of a liquid
  • Used for the thermal relay circuits and time delay circuit
  • It is used in the control devices actuated by temperature

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