PublicSensors

2.1 Temperature Sensor Intro

Overview:

Have you ever thought a spot in your room was colder or hotter than the rest?

There can be many sources of heating and cooling in a room or house beyond heating or air conditioning, such as warm lights and appliances or cold and drafty windows or walls. These sources can be hard to find but can cause temperatures to be very different from one side of a room to another. How much do your lights heat the air around them? Do windows cool or heat up a room? Are walls that face outside warmer or colder than walls that face other rooms?

Have you ever wondered why one patch of grass grows better than another?

The difference between a patch of green grass and dry grass can be due to differences in the temperature of the soil. The temperature can vary because of the amount of water in the ground, or how much shade the grass is under as the sun passes behind a nearby tree. Why is one patch of grass drier than another? How does the ground temperature change over the course of the day? How does water or shade change the temperature of the ground?

Understanding what causes differences in temperature can help us understand the world around us! The following activities will help you build your own temperature sensor and use it to investigate one or more of these questions in your own home and beyond.

Materials Needed:

Materials needed for Basic Temperature Sensor Construction and Application Activities:

Additional items needed for Advanced Sensor Construction and Application Activities:

Introduction to Temperature Sensors:

Resistors are important parts of circuits that restrict the flow of electricity (see Introduction to Circuits in Figure 1.1) While most resistors have fixed values, thermistors are fancy resistors (see Introduction to Circuits) because they change their resistance based on the temperature of the environment around them. Warm temperatures cause low resistance values, while cold temperatures cause high ones. If we know how resistance varies with temperature, we can use the thermistor to measure resistance, and then convert that resistance to the corresponding temperature. Graphs like the one below are called calibration curves, which enable you to convert a measured quantity (resistance) to its environmental significance (temperature).

Figure 2.1

Many environmental temperature sensors use thermistors to detect temperature. In this activity, you will use a digital thermistor (DS18B20) which does all of those tasks automatically. For a further challenge, try the Advanced section to build a thermistor-based temperature sensor and calculate the temperature-resistance calibration curve for yourself.