What Is An NTC Thermistor

Thermistors are temperature-sensing elements made of semiconductor material that has been sintered in order to display large changes in resistance in proportion to small changes in temperature.

This resistance can be measured by using a small and measured direct current, or dc, passed through the thermistor in order to measure the voltage drop produced.

These solid state temperature sensors actually act like electrical resistors that are temperature sensitive. That is where the name, a clear combination of the words thermal and resistor, comes from. Ametherm specializes in NTC, or negative temperature coefficient, thermistors.

Thermistors are an incredibly accurate category of temperature sensors

 

In general, thermistors are composed of sintered ceramics consisting of highly sensitive material with consistently reproducible properties of resistance versus temperature.

“The demand for thermistors has also increased in the automotive industry, especially, in applications such as powertrain, safety and controls and alternative fuel vehicles due to the change in government standards and demand patterns from the end users. A total of 30 thermistors are used in an automotive, which include 20 negative temperature coefficient (NTCs) and 5 positive temperature coefficient (PTCs) sensors. Thermistors are currently a steady growing market and is expected to continue the same trend in coming years as well.”  Sensors Online

NTC Thermistors are non-linear resistors, which alter their resistance characteristics with temperature. The resistance of NTC will decrease as the temperature increases. The manner in which the resistance decreases is related to a constant known in the electronics industry as beta, or ß. Beta is measured in °K.

NTC Thermistor Probes

 

 

 

 

Typical applications Include:

  • Temperature Measurement
  • Temperature Compensation
  • Temperature Control

You can easily calculate the resistance of NTC Thermistors at a given temperature using beta, but there is an even more accurate way to do this using the Steinhart & Hart Equation. NTC Thermistors are also an excellent alternative to semiconductor circuitry for solving temperature related problems. They can be easily used to calculate the temperature coefficient. We will provide you with guidelines for using NTC Thermistors to achieve the most accurate measurements possible.

One of the simplest ways to measure temperature using an NTC Thermistor is with a Wheatstone bridge. You can also use an NTC Thermistor temperature detection circuit to account for power dissipation. In addition, NTC Thermistors are commonly used to compensate for changes in temperature in coils and solenoids.

“Thermistors are inexpensive, easily-obtainable temperature sensors. They are easy to use and adaptable. Circuits with thermistors can have reasonable output voltages – not the millivolt outputs thermocouples have. Because of these qualities, thermistors are widely used for simple temperature measurements. They’re not used for high temperatures, but in the temperature ranges where they work they are widely used.” Bucknell University

Some basic terminology may be helpful in understanding thermistors and their potential uses. First, standard reference temperature is usually 25°C , or the temperature of the thermistor body when supposed zero-power resistance is seen. This zero-power resistance is the dc resistance value of the thermistor when measured at a specific temperature with a low enough power dissipation from the thermistor for any further power decrease resulting in no more than the smaller of 1/10 of the particular measurement tolerance or a zero point one percent change in the resistance .

Resistance ratio is a characteristic that identifies the ratio of zero-power resistance of a thermistor at 125° to the resistance at 25°C. Maximum operating temperature is the highest body temperature where the thermistor will operate with acceptable stability for an extensive time period.

This temperature should not surpass the highest value specified. Likewise, maximum power rating for thermistors is the highest power at which a thermistor will operate for a period of time while maintaining stability.

 

Ametherm’s NTC thermistors are:

  • Available in an array of designs to fit nearly any desired application
  • Created using the best high purity materials for reliable results you can count on
  • Customizable to fully meet your needs