An NTC thermistor is widely used for temperature measurement because of its high sensitivity, compact size and simple circuit design. However, an incorrect temperature reading can occur when the thermistor, circuit or installation does not match the application.
Here are 8 common causes of inaccurate NTC temperature readings and how to check them.
1. Incorrect Resistance or B Value
The resistance value and B value determine the NTC's resistance-temperature relationship.
For example, two 10 kΩ NTC thermistors can have different B values and therefore produce different resistance values at the same temperature.
Check: Confirm the NTC resistance, B value and R/T table match the specifications required by your control system.
2. Resistance Tolerance Is Too Large
Resistance tolerance directly affects temperature measurement accuracy.
For example, an NTC with a wide resistance tolerance may produce a noticeable temperature deviation even when the nominal resistance is correct.
Check: Select an appropriate resistance tolerance and B-value tolerance for your accuracy requirements.
3. The Wrong R/T Table or B Value Is Used
The controller converts resistance into temperature according to an R/T table or mathematical model.
If the actual NTC characteristics do not match the table programmed into the controller, the displayed temperature may be incorrect.
Check: Make sure the NTC's actual R/T curve, R25 and B value are consistent with the software or control algorithm.
4. Self-Heating
An NTC generates a small amount of heat when current flows through it. If the measuring current is too high, this self-heating can raise the thermistor's temperature and affect the reading.
This is especially important for small NTC elements with low thermal mass.
Check: Reduce the measurement current when possible and verify that the operating current is within the specified range.
5. Poor Thermal Contact
The NTC may be working correctly while the measured temperature is still inaccurate because it is not making good thermal contact with the object being measured.
Air gaps, poor mounting or unsuitable thermal materials can increase thermal resistance and cause measurement errors.
Check: Improve the mounting method and ensure good thermal contact between the NTC and the target surface or medium.
6. Slow Response or Incorrect Sensor Structure
The sensing element, encapsulation, probe size and protective housing all affect response time.
A large metal probe or thick encapsulation may respond more slowly than a small sensing element. When temperature changes quickly, the sensor may temporarily show a value different from the actual temperature.
Check: Select the appropriate sensor structure, size and encapsulation according to the required response time.
7. Environmental Influences
Water, humidity, oil, chemicals, vibration and high temperatures can affect the sensor or its insulation if the structure is not suitable for the environment.
For example, moisture entering the sensor assembly can cause insulation problems or long-term resistance changes.
Check: Choose appropriate waterproofing, encapsulation, probe materials and wire insulation for the operating environment.
8. Wiring or Connection Problems
Incorrect wire specifications, excessive wire resistance, loose connections or damaged insulation can also cause abnormal readings.
Long cables may be particularly important in high-precision applications.
Check: Inspect the wires, connectors and terminals, and confirm that the wiring configuration matches the measurement circuit.
Quick Troubleshooting Checklist
| Possible Cause | What to Check |
|---|---|
| Incorrect resistance | Verify R25 |
| Wrong B value | Check B25/50, B25/85, etc. |
| Wrong R/T table | Match the controller algorithm |
| Resistance tolerance | Check resistance and B-value tolerance |
| Self-heating | Check measuring current |
| Poor thermal contact | Check installation and thermal interface |
| Slow response | Check probe size and encapsulation |
| Environmental effects | Check waterproofing, materials and insulation |
| Wiring problems | Check cable, connector and terminals |
How to Improve NTC Measurement Accuracy
When an NTC reading is incorrect, it is important to check the entire measurement system, rather than only replacing the thermistor.
The NTC specification, R/T curve, measurement circuit, installation method, sensor structure and operating environment should all be considered together.
At Xinshiheng, NTC thermistors and temperature sensors can be customized according to application requirements, including resistance, B value, tolerance, temperature range, encapsulation, probe structure, wire specifications and connection methods.
Conclusion
Incorrect NTC temperature readings can have many causes, from an unsuitable B value or R/T table to self-heating, poor thermal contact and wiring problems.
By checking these factors systematically, engineers can identify the source of the error and improve temperature measurement accuracy and stability.
