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What is a Thermistor and how does it work?


What is a Thermistor?
A thermistor may be a thermally sensitive resistor that exhibits an exact and sure modification in resistance proportional to little changes in body temperature. How much its resistance can modification depends upon its distinctive composition. Thermistors are a part of a bigger cluster of passive components. And unlike their active element counterparts, passive devices are incapable of providing power gain, or amplification to a circuit.
Thermistors are made up of metallic oxides, binders and stabilizers, pressed into wafers and then cut to chip size, left in disc form, or made into another shape. The precise quantitative relation of the composite materials governs their resistance/temperature “curve.” Manufacturers typically control this ratio with great accuracy, since it determines how the thermistor will function.
Thermistor History
Michael Faraday; AN English person, first discovered the concept of thermistors in 1833 while reporting on the semiconductor behavior 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 thermistors within the 1930’s once Samuel Ruben invented the primary commercial thermistor. Since then, technology has improved; paving the road to improved manufacturing processes; along with the availability of higher quality material.
Thermistor Types
There are two types of thermistors. NTC or Negative Temperature coefficient thermistors, and PTC or Positive Temperature Coefficient thermistors. The difference is that NTC thermistors exhibit a DECREASE in resistance as body temperature will increase, whereas PTC thermistors exhibit a rise in resistance as body temperature will increase.
Benefits of NTC and PTC Thermistors
NTC Thermistors ar rugged, reliable, and stable, and that they are equipped to handle extreme environmental conditions and noise immunity additional thus than different kinds of temperature sensors.
Compact size: Packaging choices permit them to control in little or tight spaces; thereby taking on less real estate on printed circuit boards.
Fast response time: the little dimensions allow a fast response to change in temperature, which is important when immediate feedback is required.
Cost efficient: Not only ar thermistors less costly than different kinds of temperature sensors; if the purchased thermistor has the right RT curve, no different calibration is critical throughout installation or over its operational life.
Point match: the ability to get a particular resistance at a particular temperature.
Curve match: Interchangeable thermistors with the accuracy of +0.1˚C to + 0.2˚C.
How does a thermistor work?
Unlike RTDs and thermocouples, thermistors don't have standards related to their resistance vs. temperature characteristics or curves. Consequently, there are many different ones to choose from.
Each thermistor material provides a different resistance vs. temperature “curve”. Some materials give higher stability whereas others have higher resistances so they is fabricated into larger or smaller thermistors.
Many manufactures list a Beta (B) constant between a pair of temperatures (Example: [3 0/50 = 3890). This, along with the resistance at 25°C (77°F) is accustomed identity a particular thermistor curve.

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