What is NTC Thermistor ? How Does It Work?

NTC (Negative Temperature Coefficient) refers to the phenomenon and materials where electrical resistance decreases exponentially with increasing temperature, exhibiting a negative temperature coefficient.NTC materials are semiconducting ceramics typically composed of two or more metal oxides (such as manganese, copper, silicon, cobalt, iron, nickel, and zinc). These oxides are thoroughly mixed, formed, and sintered to create thermistors with a negative temperature coefficient. These ceramics’ resistivity and material constant vary depending on the composition ratio, sintering atmosphere, sintering temperature, and structural state. Additionally, non-oxide materials like silicon carbide (SiC), tin selenide (SnSe), and tantalum nitride (TaN) have emerged as NTC thermistor materials.

Most NTC semiconducting ceramics feature a spinel or similar oxide crystal structure. Their resistance can be approximated as:

R_T = R_T0 · exp[ B · (1/T - 1/T₀) ]

where:

• R_T, R_T0are the resistances at temperatures T and T₀ (in Kelvin, K), respectively.
• Bis the material constant.
• This change in resistivity with temperature stems from the intrinsic semiconductor properties of the ceramic grains.

Development History of NTC Thermistors

• 1834:Scientists first discovered the negative temperature coefficient property in silver sulfide (Ag₂S).
• 1930:Cuprous oxide-copper oxide (Cu₂O-CuO) mixtures were found to exhibit NTC behavior and were successfully used for temperature compensation in aviation instruments. Subsequent advancements in transistor technology spurred significant progress in thermistor research.
• 1960:NTC thermistors were developed.

Applications in Temperature Measurement

NTC thermistors are widely used for temperature measurement, control, and compensation, typically covering a range of -40°C to +300°C.

Working Principle of Thermistor Thermometers

Two core parameters define the temperature response of an NTC thermistor:

1. Nominal Zero-Power Resistance (R₂₅):The DC resistance was measured at the reference temperature of 25°C (298.15 K) under negligible self-heating conditions. Typical tolerance grades include ±1%, ±2%, and ±3%.
2. Material Constant (β value / B value):A dimensionless parameter characterizing temperature sensitivity, representing the thermistor’s “index of thermal sensitivity.” Common industrial β values range from 3000 K to 5000 K. It is determined using a two-temperature calibration method:
3. β = [ ln(R₁/R₂) ] / [ (1/T₁) - (1/T₂) ]
4. where R₁, R₂ are the resistances (Ω) at temperatures T₁, T₂ (K), respectively.
5. Resistance-to-Temperature Conversion Model
6. While the Steinhart-Hart equation (three-parameter model) precisely describes NTC nonlinearity, the simplified two-parameter B-parameter formulais often used in engineering practice:
7. R_T = R₂₅ · exp[ β · (1/T - 1/298.15) ]
8. The inverse conversion (resistance → temperature) is:
9. T = 1 / [ (1/298.15) + (1/β) · ln(R_T/R₂₅) ] - 273.15 (°C)
10. Where:
    • R_Tis the measured resistance (Ω) at the unknown temperature.
    • T is the absolute temperature (K) converted to Celsius (°C).

Thermistor thermometers can achieve accuracies of 0.1°C and response times as low as <0.3s. They are suitable not only for new energy vehicle thermal management, consumer electronics, and office automation but also for temperature measurement in food storage, medical hygiene, scientific agriculture, marine, deep-well, high-altitude, and glacial environments.

EXSENSE, recognized as a National High-Tech Enterprise and Specialized and Sophisticated SME, specializes in developing temperature sensing products, including NTC chips, thermistors, and temperature sensors. Our vision is “ Strive to be world-class, build a thriving EXSENSE.” We are committed to continuously improving our management systems, attracting top talent, strengthening quality awareness, and implementing brand strategy. We aim to establish EXSENSE as a world-leading manufacturer of high-quality NTC thermistors and temperature sensors within China’s electronics industry, propelling the EXSENSE brand onto the global stage!