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A thermistor becomes a useful temperature sensor only after its output is related to temperature. Calibrate the complete potential divider and choose a switching voltage from the measured response.
What you'll be able to do
Connect an NTC thermistor and suitable fixed resistor in series across a stable low-voltage supply. Measure output across the chosen component with a high-resistance voltmeter or logger. In an NTC thermistor, resistance falls as temperature rises.
If output is across the thermistor in the lower divider position, warming reduces the output. If output is across the fixed lower resistor with the thermistor above it, warming increases output. State the arrangement explicitly: “voltage falls with temperature” is not true for every wiring choice.
Place a suitable insulated or protected thermistor and an independent thermometer in a stirred water bath, following the approved electrical and hot-water procedure. Vary temperature over a useful range and wait for the sensor and thermometer to reach equilibrium before recording temperature and output voltage.
Plot measured output voltage against temperature and repeat readings while cooling to check lag and reproducibility. Use the calibration curve to identify the output corresponding to a chosen thermostat set point. An NTC response is generally non-linear, so do not force a single straight line over a broad range without justification.
A thermostat switching stage compares sensor output with a reference corresponding to the set point. Explain which output direction should switch heating on or off. The core measurement is calibration; detailed amplifier circuit design is not required here.
A large measuring current self-heats the thermistor, making it warmer than the bath. Keep current appropriately small, use a stable supply and consider loading by the measuring or switching circuit. Position the thermometer close enough to sample the same temperature and allow time for equilibration; taking readings faster can increase systematic lag rather than improve precision.
Try each problem before opening the worked solution. State the physical model, show substitutions with consistent units, and explain what your answer means.
Equation recap
Common mistakes to avoid
Key takeaways
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.