NTC Thermistor Calculator

An NTC (Negative Temperature Coefficient) thermistor is a type of resistor whose resistance decreases as its temperature increases. These semiconductor devices are highly temperature-sensitive and find applications in thermostats, temperature sensors, and protection systems.

We use NTC thermistors in Wheatstone bridge configurations with precision analog-to-digital converters for remote temperature measurements.

The formula

The resistance at a given temperature is calculated using the Beta equation:

R(T) = R0 x exp(B x (1/T - 1/T0))

Where:

• R0 — reference resistance in ohms (typically at 25 C)
• T0 — reference temperature in Kelvin
• B (Beta) — characteristic constant of the thermistor
• T — target temperature in Kelvin

The formula works by comparing the inverse of the absolute (Kelvin) temperatures of the target and reference points. The Beta constant amplifies the differences for precise modelling.

Parameters

• Reference resistance (R0): the nominal resistance at the reference temperature, typically 10k ohms at 25 C
• Reference temperature (T0): usually 25 C (298.15 K)
• Beta constant (B): provided in the thermistor datasheet, typically 3000-4000 for common NTC devices
• Target temperature (T): the temperature at which you want to know the resistance