Temperature Measurement System

This lab uses a NTC 10K @ 25ºC thermistor to measure the temperature. The thermistor has a linear relation between the temperature and its resistance within a certain range. For this specific thermistor in the lab, the resistance is 11.18 kΩ at 25 ºC and 6.65 kΩ at 37 ºC.

The calculation shows the predicted output voltage at 25 ºC and 37 ºC.  The theoretical resistor we need in the circuit is 4.633 kΩ. In order to have the output voltage increase by a minimum of 0.5V over a temperature range of 25 ºC to 37 ºC, we picked a resistor of 4.7 kΩ to connect in series. It guarantees the voltage range out of all the resistor selections available.

 Here is the setup of the circuit:

Here are two videos showing the change of voltage when the temperature increases. The temperature rises from 1.43V to 1.98V. It creates a voltage difference of 0.55V. The theoretical value is 0.51V. The percent difference between the experimental drop and the theoretical drop is 7.27%.

Summary: This experiment shows that a thermistor can be used to control the output voltage by connecting them in series. A voltage divider circuit with a thermistor can use the temperature as a variable to control how much voltage is delivered to a specific load. By changing the resistance and power supply, thermistor can cover various range of voltage when it is in a certain temperature interval. Also, by measuring the voltage of the load, we can calculate the current temperature since the thermistor has a fixed value of resistance corresponding to a certain temperature.