Introduction
NTC thermistors are widely used for temperature measurement and control. When selecting an NTC thermistor, two important specifications are nominal resistance (R25) and resistance tolerance.
Understanding these parameters helps engineers choose the right thermistor for accurate and reliable temperature sensing.
1. What Is NTC Resistance Value?
An NTC thermistor is a temperature-sensitive resistor whose resistance decreases as temperature increases.
The resistance value is usually specified at a reference temperature, most commonly 25°C, and is expressed in ohms (Ω) or kilohms (kΩ).
Common nominal resistance values include:
- 2 kΩ
- 5 kΩ
- 10 kΩ
- 20 kΩ
- 50 kΩ
- 100 kΩ
The appropriate resistance depends on the measurement circuit, operating temperature range and application requirements.
2. What Is R25?
R25 is the nominal resistance of an NTC thermistor at 25°C.
For example, a 10 kΩ NTC thermistor has a nominal resistance of 10,000 Ω at 25°C. Its resistance will be higher at lower temperatures and lower at higher temperatures.
R25 is a key parameter for matching the thermistor with a controller or measurement circuit. However, R25 alone does not define the full resistance-temperature relationship. The B value and the R/T characteristic must also be considered.
3. What Is Resistance Tolerance?
Resistance tolerance indicates how much the actual resistance may deviate from its nominal value at the specified reference temperature.
For example, a 10 kΩ NTC thermistor with ±1% resistance tolerance has an allowable resistance range of:
- Minimum: 9.9 kΩ
- Nominal: 10 kΩ
- Maximum: 10.1 kΩ
A tighter tolerance can help improve consistency between sensors, which is important in applications requiring precise temperature measurement or interchangeable components.
4. How to Choose the Right Resistance and Tolerance
When selecting an NTC thermistor, consider these factors:
- Resistance value: Match the controller and circuit design.
- B value: Ensure the resistance-temperature curve matches the application.
- Resistance tolerance: Select according to the required measurement accuracy.
- Operating temperature range: Confirm the thermistor meets the application's temperature requirements.
Remember that resistance tolerance is not the same as temperature accuracy. The B-value tolerance, measurement circuit, calibration and installation can also affect the final temperature reading.
Conclusion
R25 defines an NTC thermistor's nominal resistance at 25°C, while resistance tolerance specifies the permitted variation from that value. Choosing the right combination of resistance, B value and tolerance helps achieve reliable temperature measurement.
Xinshiheng provides customized NTC thermistors and temperature sensors with different resistance values, B values, tolerances, temperature ranges, encapsulation structures and wire specifications. Contact our team for support with your application requirements.
