How to Select an NTC Thermistor?
In circuit design, a target resistance range is usually defined first. Within this range, the sampling points on the R-T curve should be distributed as evenly as possible, and the resistance difference between adjacent temperature points should be maximized to improve temperature resolution and measurement accuracy.
Therefore, suitable NTC thermistor models can be selected by evaluating the R-T characteristic curve determined by R25 (the zero-power resistance at 25 °C) and the B value, ensuring it meets the design requirements.
How to Obtain a More Linear Temperature–Voltage Curve with Higher Resolution
Since the resistance of an NTC thermistor changes exponentially and decreases rapidly with temperature, a series resistor is typically added. This prevents excessive current under certain temperature conditions that could damage the NTC. Additionally, placing a resistor in parallel with the NTC can modify the slope of the curve, further optimizing temperature-reading resolution.
As shown in the figure below, after adding a 10 kΩ parallel resistor, the slope is significantly reduced and the curve becomes much more linear, indicating improved temperature resolution.
Based on application requirements, an appropriate B value and nominal resistance can be selected, and series/parallel resistors can be added so that the microcontroller's ADC reads a temperature–voltage curve that is as linear as possible and has higher resolution within the desired temperature range.
