NTC Thermistor Temperature Sensing Experiment

Introduction to NTC Thermistors

An NTC (Negative Temperature Coefficient) thermistor is a temperature-sensitive resistor whose resistance decreases as temperature increases. NTC thermistors are commonly used in temperature sensing and temperature compensation circuits because of their reliability and sensitivity.

In this experiment, we will use an NTC thermistor to measure temperature changes by monitoring the resistance variation as the temperature fluctuates. This experiment will provide insights into how thermistors can be used in temperature monitoring systems.

Theory Behind NTC Thermistors

NTC thermistors have a predictable resistance-temperature characteristic. As the temperature increases, the resistance of the thermistor decreases in a non-linear fashion. The relationship between resistance and temperature can be modeled using the Steinhart-Hart equation for more precise temperature measurements.

In simpler applications, a voltage divider circuit is used, where the NTC thermistor is combined with a fixed resistor. The output voltage of the divider changes as the thermistor’s resistance varies with temperature, providing a measurable voltage that corresponds to temperature.

Circuit Diagram

The following circuit demonstrates an NTC thermistor used in a voltage divider for temperature measurement:

The thermistor (R_thermistor) is connected in series with a known fixed resistor (R_fixed). The voltage across the thermistor is measured and used to calculate the corresponding temperature based on the thermistor's resistance characteristics.

Experiment: NTC Thermistor Temperature Sensing

To perform this experiment, you will need the following components:

• 1 NTC thermistor (e.g., 10kΩ at 25°C)
• 1 fixed resistor (e.g., 10kΩ)
• DC power supply (5V)
• Multimeter (to measure voltage)
• Breadboard and jumper wires
• Optional: Arduino or any microcontroller for data logging

Steps to Conduct the Experiment:

1. Set up the circuit as shown in the circuit diagram, with the thermistor in series with the fixed resistor to form a voltage divider.
2. Apply a constant DC voltage (e.g., 5V) to the voltage divider circuit.
3. Measure the voltage across the thermistor using a multimeter.
4. Expose the thermistor to different temperatures (e.g., by heating it with your hand or placing it in warm water).
5. Record the voltage across the thermistor at each temperature.
6. Optional: If using an Arduino, connect the output of the voltage divider to an analog input pin, and write code to convert the measured voltage to temperature values using the thermistor’s resistance-temperature curve or the Steinhart-Hart equation.

By observing the changes in voltage as the temperature fluctuates, you can relate the measured voltage to temperature variations.

Calculation of Temperature

To calculate the temperature from the thermistor’s resistance, you can use the following approximation:

        Temperature (T) = 1 / (A + B * ln(R) + C * ln(R)^3) - 273.15
        

Where:

• T is the temperature in Celsius.
• R is the resistance of the thermistor in ohms.
• A, B, and C are the Steinhart-Hart coefficients (provided in the thermistor's datasheet).

If you're using an Arduino, you can simplify the calculation by using pre-calibrated lookup tables or polynomial equations based on the specific thermistor's datasheet.

Applications of NTC Thermistors

NTC thermistors are widely used in various applications such as:

• Temperature sensors for HVAC systems and home appliances
• Battery management systems for temperature monitoring
• Automotive temperature sensing (engine temperature, cabin temperature)
• Thermal protection for electronic circuits
• Industrial temperature monitoring systems

Conclusion

In this experiment, you have explored how NTC thermistors can be used to sense temperature by measuring their resistance variation with changing temperature. Thermistors are reliable, cost-effective components for temperature measurement and are widely used in many industrial and consumer applications. By understanding how to implement a voltage divider circuit with a thermistor, you can easily build a simple yet effective temperature sensor.