Making Sense of Sensors

This lesson focuses on the hygrometer, a sensor used to measure humidity. Students work in teams to design and build a hygrometer out of everyday items to measure humidity levels.

Learn about engineering design.
Learn about instrumentation.
Learn about planning and construction.
Learn about teamwork and working in groups.

Age Levels: 8-18

Build Materials (For each team)

Required Materials (Trading/Table of Possibilities)

Cotton balls
Tissue paper
Cardboard
Litmus paper
Writing paper
Wood blocks
Plastic or paper cups
Straws
Aluminum foil
Rubber bands
Toothpicks
Paper towels
Wire

Testing Materials

Water spray bottle, with mist option

Testing Materials & Process

Materials

Water spray bottle, with mist option

Process

Have teams leave their hygrometer designs overnight to generate a base “reading” of humidity.

The next day, teams should record the “normal” humidity measurement on their student worksheet. Then, expose each team’s hygrometer to humidity by using a series of sprays of mist/water. Teams should mark their hygrometer “readings” after each of the following:

Reading before exposure to mist
Reading after exposure to 4 sprays of mist
Reading after exposure to 8 sprays of mist
Reading after exposure to 16 sprays of mist

Engineering Design Challenge

Design Challenge

You are part of a team of engineers who have been given the challenge of developing a hygrometer – an instrument that detects changes in humidity. You will likely have to incorporate a pivot and gauge within your hygrometer. The goal is to be able to report a change in the humidity in your classroom.

Criteria

Must draw the scale that you will use to “measure” changes in humidity. You may use numbers or words in your scale.
Design must be left in the classroom overnight to generate a “base reading” of the humidity level.

Constraints

Use only the materials provided.
Teams may trade unlimited materials.

Activity Instructions & Procedures

Break class into teams of 2-3. This activity must be completed over 2 days – to allow for a base humidity reading to be achieved.
Hand out the Making Sense of Sensors worksheet, as well as some sheets of paper for sketching designs.
Discuss the topics in the Background Concepts Section. Consider asking students how temperature is measured. What tool is used? Does humidity get measured the same way? Is there a special tool needed to measure humidity?
Review the Engineering Design Process, Design Challenge, Criteria, Constraints and Materials.
Provide each team with their materials.
Explain that students must work as a team to design a hygrometer out of everyday materials that can indicate a change in humidity. Explain that they may base their design on a pivoting gauge (such as the Coventry Hygrometer) or they may come up with their own design.
Announce the amount of time they have to design and build (1 hour recommended).
Use a timer or an on-line stopwatch (count down feature) to ensure you keep on time. (www.online-stopwatch.com/full-screen-stopwatch). Give students regular “time checks” so they stay on task. If they are struggling, ask questions that will lead them to a solution quicker.
Students meet and develop a plan for their hygrometer. They agree on materials they will need, write/draw their plan, and present their plan to the class. Teams may trade unlimited materials with other teams to develop their ideal parts list.
Teams build their designs.
Teams leave their hygrometer designs overnight to generate a base “reading” of humidity.
The next day, teams should record the “normal” humidity measurement on their student worksheet. Then, expose each team’s hygrometer to humidity by using a series of sprays of mist/water. Teams should mark their hygrometer “readings” after each of the following:

Reading before exposure to mist
Reading after exposure to 4 sprays of mist
Reading after exposure to 8 sprays of mist
Reading after exposure to 16 sprays of mist

As a class, discuss the student reflection questions.
For more content on the topic, see the “Digging Deeper” section.

Student Reflection (engineering notebook)

Did you succeed in creating a hygrometer that indicated a change in humidity?
What aspect of your design do you think worked best? Why?
What hygrometer “engineered” by another student team did you find most inspiring? How did it work better than yours, or what feature did you appreciate that the other team came up with?
Did you decide to revise your original design while in the construction phase? Why? How?
Hygrometers have been measuring humidity for hundreds of years. Do you think that technology has improved the hygrometer? How?
How durable do you think your hygrometer is? Would it be able to continue to work for a week, two weeks, a year, a decade? What would you have to do to your hygrometer to make it reliable for a longer period of time?
Do you think you would have been able to complete this project easier if you were working alone? Explain…
If you could have used a material or materials that were not provided to you, what would you have requested? Why do you think this material might have helped with the challenge?
Can you identify five sensors in your school building?
What was your favorite part of the challenge? Design Phase? Building Phase? Testing Phase? Why?

Time Modification

The lesson can be done in as little as 1 class period for older students. However, to help students from feeling rushed and to ensure student success (especially for younger students), split the lesson into two periods giving students more time to brainstorm, test ideas and finalize their design. Conduct the testing and debrief in the next class period.

Engineering Design Process

Background Concepts

What is Humidity?

Humidity is the amount of water vapor in the air. In daily language the term “humidity” is normally taken to mean relative humidity.

Relative humidity is defined as the ratio of the partial pressure of water vapor in a parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature. Humidity may also be expressed as absolute humidity and specific humidity. Relative humidity is an important metric used in forecasting weather. Humidity indicates the likelihood of precipitation, dew, or fog. High humidity makes people feel hotter outside in the summer because it reduces the effectiveness of sweating to cool the body by preventing the evaporation of perspiration from the skin. This effect is calculated in a heat index table.

Measuring Relative Humidity

The measurement of relative humidity requires two facts: the temperature, and the dew point. The dew point is the temperature the air must be cooled to in order for condensation to occur. The higher the humidity, the closer the dew point is to the air temperature. When the humidity is 100 percent, the dew point and the temperature are the same. The dew point can never be higher than the temperature of the air at any given time.

Humidity can be measured in several different ways, but most commonly humidity is reported as the “relative humidity.” Relative humidity is the ratio of the amount of moisture in the air compared to the amount the air is capable of holding at a given temperature, expressed as a percentage. An online humidity calculator may be found online at the National Weather Service Meteorological Conversions and Calculations website at www.wpc.ncep.noaa.gov/html/heatindex.shtml.

Engineering Implications

Engineers in many disciplines must consider humidity levels in their work. A civil engineer, for example, might be designing a building to house rare books which might be damaged by excessive moisture. Or, an air conditioning and refrigeration engineer might be developing a system to protect rare tapestries in a museum. Chemical and petroleum engineers may face situations where gases and condensing vapors co-exist. Reliable tools are important to engineers as they solve the challenges they face in many fields.

What are Sensors?

Why We Use Sensors

Sensors are devices that measure something about the environment and either causes a reaction to take place or reports data which can be read by a person.

For example, a thermometer measures the temperatures outside, or might measure a person’s temperature. Some businesses and homes have “low temperature sensors” which trigger a phone call to a property owner to let them know that the temperature in a building has dropped to a dangerous level which might cause pipes to freeze.

Another type of a sensor is a light sensor, which causes a light to turn on, for example when it becomes dark outside. These are popular in outdoor lighting, and are often solar powered and turn on an exterior light at dusk and off at dawn.

Another sensor is a motion sensor. These are used in burglar alarm systems and also often trigger lights to turn on. For example, the light to the right might be mounted outside a building so when someone walked to an entryway, a light would turn on to guide the way. Some cameras now have motion sensors built in too. They are used to photograph wildlife while not disturbing the animals.

Sensors are also used in familiar devices such as touch sensitive elevator buttons or special computer screens. And hundreds of sensors can be found in the average car — keeping track of everything from how much gas is left in a tank to how pressured the tires are.

How Do Sensors Work?

Every type of sensor operates a little differently. For example, a mercury thermometer shows temperature changes because the liquid mercury expands or contracts up or down a calibrated glass tube with a scale printed on it. Motion sensors might have a beam of light crossing a doorway, or might incorporate radar. For example many grocery store doors open automatically when a customer walks toward the door and causes the radar to bounce back, triggering a response by a motor which opens the door. Some motion sensors detect infrared energy, in the form of heat from a person or animal which might trigger a light to turn on. And, to maintain accuracy, all sensors need to be calibrated from time to time.

What is a Hygrometer?

How Hygrometers Work

Hygrometers are instruments used for measuring humidity. It measures water vapor content in the air and communicates changes in humidity visibly and immediately through a graph or a dial. There are several types including:

Hair hygrometer – uses a human hair as the sensing instrument. The hair lengthens when the air is moist and contracts when the air is dry, but remains unaffected by air temperature. This system works, but the hair does not respond instantly to changes and requires time for measurement.
Mechanical hygrometer – uses absorbent paper as the sensing instrument. The paper becomes heavier as it absorbs water from the air.
Electric hygrometer – uses a plate coated with carbon. Electrical resistance of the carbon coating changes as the moisture content of the air changes.
Infrared hygrometer – uses a beam of light containing two separate wave lengths to gauge atmospheric humidity. One of the wavelengths is absorbed by water vapor, the other is unaffected, providing an extremely accurate index of water vapor for paths of a few inches or thousands of feet.

Coventry Hygrometer

A nice, old example is the Coventry Hygrometer. It is based on how paper expands and contracts with changes in moisture. It is housed at the Science Museum in London, was invented by John Coventry, and made by George Adams the Younger in about 1790. It provides a very simple measure of the moisture in the air and was widely used by chemists and naturalists. A pile of paper discs soaked in brine was suspended on one arm of a balance. The other arm moved over a scale. The paper absorbed water in the atmosphere and so became heavier in humid conditions, tipping the scale as an indication of humidity.

Vocabulary

Constraints: Limitations with material, time, size of team, etc.
Criteria: Conditions that the design must satisfy like its overall size, etc.
Electric Hygrometer: Uses a plate coated with carbon. Electrical resistance of the carbon coating changes as the moisture content of the air changes.
Engineers: Inventors and problem-solvers of the world. Twenty-five major specialties are recognized in engineering (see infographic).
Engineering Design Process: Process engineers use to solve problems.
Engineering Habits of Mind (EHM): Six unique ways that engineers think.
Hair Hygrometer: Uses a human hair as the sensing instrument. The hair lengthens when the air is moist and contracts when the air is dry, but remains unaffected by air temperature. This system works, but the hair does not respond instantly to changes and requires time for measurement.
Humidity: The amount of water vapor in the air. In daily language the term “humidity” is normally taken to mean relative humidity.
Hygrometer: Instruments used for measuring humidity.
Infrared Hygrometer: Uses a beam of light containing two separate wavelengths to gauge atmospheric humidity. One of the wavelengths is absorbed by water vapor, the other is unaffected, providing an extremely accurate index of water vapor for paths of a few inches or thousands of feet.
Iteration: Test & redesign is one iteration. Repeat (multiple iterations).
Mechanical Hygrometer: Uses absorbent paper as the sensing instrument. The paper becomes heavier as it absorbs water from the air.
Pivoting Gauge (such as the Coventry Hygrometer): Provides a very simple measure of the moisture in the air and was widely used by chemists and naturalists.
Prototype: A working model of the solution to be tested.
Relative Humidity: The ratio of the partial pressure of water vapor in a parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature.
Sensors: Devices that measure something about the environment and either causes a reaction to take place or reports data which can be read by a person.

Dig Deeper

Internet Connections

National Weather Service Meteorological Conversions and Calculations

Recommended Reading

A Treatise On Meteorology: The Barometer, Thermometer, Hygrometer, Rain-Gauge And Ozonometer (ISBN: 1409788326)
Temperature And Humidity Measurement (ISBN: 9814021091)
Humidity Control Design Guide for Commercial And Institutional Buildings (ISBN: 1883413982)

Writing Activity

Write an essay or a paragraph about why a civil engineer developing a new museum to house watercolor paintings might be concerned about humidity.

Curriculum Alignment

Alignment to Curriculum Frameworks

Note: Lesson plans in this series are aligned to one or more of the following sets of standards:

U.S. Science Education Standards (http://www.nap.edu/catalog.php?record_id=4962)
U.S. Next Generation Science Standards (http://www.nextgenscience.org/)
International Technology Education Association’s Standards for Technological Literacy (http://www.iteea.org/TAA/PDFs/xstnd.pdf)
U.S. National Council of Teachers of Mathematics’ Principles and Standards for School Mathematics (http://www.nctm.org/standards/content.aspx?id=16909)
U.S. Common Core State Standards for Mathematics (http://www.corestandards.org/Math)
Computer Science Teachers Association K-12 Computer Science Standards (http://csta.acm.org/Curriculum/sub/K12Standards.html)

National Science Education Standards Grades K-4 (ages 4 – 9)

CONTENT STANDARD A: Science as Inquiry

As a result of activities, all students should develop

Abilities necessary to do scientific inquiry

CONTENT STANDARD B: Physical Science

As a result of the activities, all students should develop an understanding of

Properties of objects and materials
Position and motion of objects

CONTENT STANDARD D: Earth and Space Science

As a result of their activities, all students should develop an understanding of

Changes in earth and sky

CONTENT STANDARD E: Science and Technology

As a result of activities, all students should develop

Abilities of technological design

CONTENT STANDARD F: Science in Personal and Social Perspectives

As a result of activities, all students should develop understanding of

Changes in environments
Science and technology in local challenges

National Science Education Standards Grades 5-8 (ages 10 – 14)

CONTENT STANDARD A: Science as Inquiry

As a result of activities, all students should develop

Abilities necessary to do scientific inquiry

CONTENT STANDARD B: Physical Science

As a result of their activities, all students should develop an understanding of

Properties and changes of properties in matter

CONTENT STANDARD E: Science and Technology

As a result of activities in grades 5-8, all students should develop

Abilities of technological design
Understandings about science and technology

CONTENT STANDARD F: Science in Personal and Social Perspectives

As a result of activities, all students should develop understanding of

Populations, resources, and environments
Risks and benefits
Science and technology in society

National Science Education Standards Grades 9-12 (ages 14-18)

CONTENT STANDARD A: Science as Inquiry

As a result of activities, all students should develop

Abilities necessary to do scientific inquiry

CONTENT STANDARD B: Physical Science

As a result of their activities, all students should develop understanding of

Structure and properties of matter

CONTENT STANDARD E: Science and Technology

As a result of activities, all students should develop

Abilities of technological design
Understandings about science and technology

CONTENT STANDARD F: Science in Personal and Social Perspectives

As a result of activities, all students should develop understanding of

Science and technology in local, national, and global challenges

CONTENT STANDARD G: History and Nature of Science

As a result of activities, all students should develop understanding of

Nature of scientific knowledge
Historical perspectives

Next Generation Science Standards Grades 3-5 (Ages 8-11)

Motion and Stability: Forces and Interactions

Students who demonstrate understanding can:

3-PS2-1. Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object.

Engineering Design

Students who demonstrate understanding can:

3-5-ETS1-1.Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost.
3-5-ETS1-2.Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.
3-5-ETS1-3.Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.

Next Generation Science Standards Grades 6-8 (Ages 11-14)

Engineering Design

Students who demonstrate understanding can:

MS-ETS1-1 Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.
MS-ETS1-2 Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

Standards for Technological Literacy – All Ages

The Nature of Technology

Standard 3: Students will develop an understanding of the relationships among technologies and the connections between technology and other fields of study.

Technology and Society

Standard 6: Students will develop an understanding of the role of society in the development and use of technology.
Standard 7: Students will develop an understanding of the influence of technology on history.

Design

Standard 9: Students will develop an understanding of engineering design.
Standard 10: Students will develop an understanding of the role of troubleshooting, research and development, invention and innovation, and experimentation in problem solving.

Abilities for a Technological World

Standard 11: Students will develop abilities to apply the design process.
Standard 13: Students will develop abilities to assess the impact of products and systems.

The Designed World

Standard 17: Students will develop an understanding of and be able to select and use information and communication technologies.

Student Worksheet

You are part of a team of engineers who have been given the challenge of developing an instrument to detect changes in humidity — a hygrometer. You’ll have lots of materials to choose from, and will likely have to incorporate a pivot and gauge within your hygrometer. If your system works, you’ll be able to report a change in the humidity in your classroom. How you accomplish the task is up to your team!.

Planning Stage

Meet as a team and discuss the problem you need to solve. You’ll need to determine which materials you’ll request from the many everyday items your teacher has available. As a team, come up with your best design and draw it in the box below. Be sure to indicate the materials you anticipate using, including the quantity you’ll request from your teacher. Present your design to the class. You may choose to revise your teams’ plan after you receive feedback from class.

Design:

Materials Needed:

In the box below, draw the scale that you will use to “measure” changes in humidity. You may use numbers or words in your scale. You may wish to copy the one you draw to use within your hygrometer, or make another one that fits the size of your instrument during construction.

Scale: Example:

Construction Phase

Build your hygrometer. During construction you may decide you need additional items or that your design needs to change. This is ok — just make a new sketch and revise your materials list. You may want to trade items with other teams, or request additional materials from your teacher.

Testing Phase

Leave your hygrometer overnight to generate a base “reading” of humidity. The next day, record the “normal” humidity measurement in the box below.

Next, the hygrometers will be exposed to humidity by a series of sprays of mist/water. Mark your hygrometers “readings” after each spray.

Reading on Hygrometer before exposure to mist

Reading on Hygrometer after exposure to 4 sprays of mist

Reading on Hygrometer after exposure to 8 sprays of mist

Reading on Hygrometer after exposure to 16 sprays of mist

Evaluation Phase

Teams then complete an evaluation/reflection worksheet, and present their findings to the class.

Did you succeed in creating a hygrometer that indicated a change in humidity?

What aspect of your design do you think worked best? Why?

What hygrometer “engineered” by another student team did you find most inspiring? How did it work better than yours, or what did feature did you appreciate that the other team came up with?

Did you decide to revise your original design while in the construction phase? Why? How?

Hygrometers have been measuring humidity for hundreds of years. Do you think that technology has improved the hygrometer? How?

How durable do you think your hygrometer is? Would it be able to continue to work for a week, two weeks, a year, a decade? What would you have to do to your hygrometer to make it reliable for a longer period of time?

Do you think you would have been able to complete this project easier if you were working alone? Explain…

If you could have used a material or materials that were not provided to you, what would you have requested? Why do you think this material might have helped with the challenge?