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IoT-For-Beginners/translations/en/2-farm/lessons/2-detect-soil-moisture/assignment.md

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Calibrate your sensor

Instructions

In this lesson, you collected soil moisture sensor readings, measured as values ranging from 0 to 1023. To convert these into actual soil moisture readings, you need to calibrate your sensor. This involves taking readings from soil samples and calculating the gravimetric soil moisture content from these samples.

You will need to repeat these steps multiple times to gather the necessary readings, using soil with varying levels of wetness each time.

  1. Take a soil moisture reading using the soil moisture sensor. Record this reading.

  2. Collect a sample of the soil and weigh it. Record this weight.

  3. Dry the soil—using a warm oven at 110°C (230°F) for a few hours is ideal. Alternatively, you can dry it in sunlight or place it in a warm, dry area until the soil is completely dry. The soil should become powdery and loose.

    💁 In a laboratory setting, for the most accurate results, you would dry the soil in an oven for 48-72 hours. If your school has drying ovens, see if you can use them for a longer duration. The longer the drying time, the drier the sample and the more accurate the results.

  4. Weigh the soil again.

    🔥 If you dried the soil in an oven, ensure it has cooled down before weighing!

The gravimetric soil moisture is calculated as:

soil moisture % is weight wet minus weight dry, divided by weight dry, times 100

  • W
    • the weight of the wet soil
  • W
    • the weight of the dry soil

For example, suppose you have a soil sample that weighs 212g when wet and 197g when dry.

The calculation filled in

  • W = 212g
  • W = 197g
  • 212 - 197 = 15
  • 15 / 197 = 0.076
  • 0.076 * 100 = 7.6%

In this example, the soil has a gravimetric soil moisture of 7.6%.

Once you have readings for at least three samples, plot a graph of soil moisture percentage against soil moisture sensor readings. Add a line of best fit to the points. You can then use this graph to determine the gravimetric soil moisture content for a given sensor reading by referencing the value on the line.

Rubric

Criteria Exemplary Adequate Needs Improvement
Gather calibration data Collect at least 3 calibration samples Collect at least 2 calibration samples Collect at least 1 calibration sample
Make a calibrated reading Successfully plot the calibration graph, make a reading from the sensor, and convert it to gravimetric soil moisture content Successfully plot the calibration graph Unable to plot the graph

Disclaimer:
This document has been translated using the AI translation service Co-op Translator. While we aim for accuracy, please note that automated translations may include errors or inaccuracies. The original document in its native language should be regarded as the authoritative source. For critical information, professional human translation is advised. We are not responsible for any misunderstandings or misinterpretations resulting from the use of this translation.