Focusens MF5A-5 103F3977BT461 NTC Thermistor - 10 kΩ at 25°C, B3977K

The B value, specifically B25/85 = 3977K ±1%, defines the resistance-temperature relationship of the NTC thermistor between 25°C and 85°C. This precise constant is critical for calculating accurate temperature from measured resistance using the Steinhart-Hart equation or lookup tables in your microcontroller firmware.

Connect the thermistor as part of a voltage divider circuit with a fixed precision resistor (e.g., 10 kΩ) between your microcontroller's analog input pin and ground. Measure the voltage at the divider's midpoint. You must then convert this ADC reading to resistance and use the thermistor's B value or a calibration table to compute the temperature in your code.

To prevent self-heating errors, ensure the excitation current through the thermistor is minimized. Operate the sensor at or below its maximum power rating of 60 mW. In practice, use a high-value series resistor in your voltage divider and sample the analog input intermittently rather than continuously to allow the sensor to return to ambient temperature.

The time constant (τ ≤16 sec in still air) indicates how quickly the thermistor responds to a step change in ambient temperature. It represents the time required to reach 63.2% of the total temperature difference. For dynamic measurements or control loops, this parameter defines the sensor's speed and must be accounted for to avoid lag in your system's response.