Moisture sensor

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Quick Questions

Shade in the A or B circle for each question.

1. A moisture sensor measures the amount of water in which of these?

A The air in a room

B A solid material such as soil

2. Which sensor would an automatic plant watering system use to check if the soil is dry?

A Moisture sensor

B Humidity sensor

3. True or false: a moisture sensor and a humidity sensor measure exactly the same thing.

A False

B True

4. A farmer wants to know whether a field needs irrigating. Which sensor data is most useful?

A Water content of the soil

B Water vapour in the air

5. A grain store must stop the grain getting too damp and going mouldy. Which sensor checks the grain itself?

A Light sensor

B Moisture sensor

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1moisture sensor		AThe wrong sensor is used. Water content of soil is measured with a moisture sensor, while a humidity sensor measures the air.
2humidity sensor		BAn input device that measures the amount of water in a solid material such as soil
3Automatic plant watering: the sensor reads the water content of the soil and the pump turns on when the soil is too dry		CAn input device that measures the amount of water vapour in the air, not in a solid
4Grain storage: the sensor measures the water content of stored grain so that it does not go mouldy		DIF moisture < 30 THEN pump ← ON
5A moisture sensor measures the water vapour in the air in a greenhouse		EThis describes a humidity sensor. A moisture sensor measures the water in a solid such as soil, not the air.
6A farmer uses a humidity sensor pushed into the soil to decide when to water the crops		FIF grainMoisture > 14 THEN alarm ← ON

Definitions

moisture sensor

Fill in the Blanks

Complete each line of code by filling in the missing parts.

moisture ← ___________("soil")

IF moisture _ 30 THEN pump ← ON ENDIF

IF moisture < 30 ____ pump ← ON ENDIF

IF moisture > 60 THEN pump ← ___

_____ moisture < 30 pump ← ON ENDWHILE

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A moisture ← READ(soilSensor)

B IF moisture > 30 THEN

C pump ← ON

D ENDIF

Question 2

A moisture ← READ(soilSensor)

B IF moisture < 25 THEN

C OUTPUT Water the plant

D ENDIF

Question 3

A // Grain store monitoring

B grainMoisture ← READ(sensor)

C IF grainMoisture > 14 THEN

D OUTPUT "Grain too dry"

E ENDIF

Question 4

A // Measure water in soil

B reading ← humiditySensor(soil)

C IF reading < 40 THEN

D pump ← ON

Question 5

A field ← READ(fieldSensor)

B IF field < 35 THEN

C valve ← CLOSED

D ELSE

E valve ← CLOSED

Answer Key

Moisture sensor

Section A: Quick Questions

B — A solid material such as soil

A — Moisture sensor

A — False

A — Water content of the soil

B — Moisture sensor

Section B: Match the Pairs

moisture sensor → An input device that measures the amount of water in a solid material such as soil

humidity sensor → An input device that measures the amount of water vapour in the air, not in a solid

Automatic plant watering: the sensor reads the water content of the soil and the pump turns on when the soil is too dry → IF moisture < 30 THEN pump ← ON

Grain storage: the sensor measures the water content of stored grain so that it does not go mouldy → IF grainMoisture > 14 THEN alarm ← ON

A moisture sensor measures the water vapour in the air in a greenhouse → This describes a humidity sensor. A moisture sensor measures the water in a solid such as soil, not the air.

A farmer uses a humidity sensor pushed into the soil to decide when to water the crops → The wrong sensor is used. Water content of soil is measured with a moisture sensor, while a humidity sensor measures the air.

Section C: Definitions

moisture sensor — An input device that measures the amount of water in a solid material such as soil. Used in automatic plant watering and farming. Not the same as a humidity sensor, which measures air.

Section D: Fill in the Blanks

moisture ← READ_SENSOR("soil")

IF moisture < 30 THEN
  pump ← ON
ENDIF

IF moisture < 30 THEN
  pump ← ON
ENDIF

IF moisture > 60 THEN pump ← OFF

WHILE moisture < 30
  pump ← ON
ENDWHILE

Section E: Spot the Error

B — A low reading means the soil is dry, so the pump should switch on when moisture is below the threshold. It should be IF moisture < 30 THEN.

C — Text to be displayed must be inside quotation marks. It should be OUTPUT "Water the plant".

D — The condition tests for a HIGH moisture reading, so the grain is too damp, not too dry. The message should be "Grain too damp".

B — A humidity sensor measures water in the air. Water in soil is measured by a moisture sensor, so it should be moistureSensor(soil).

C — When the field reading is below 35 the soil is too dry, so the irrigation valve must be opened. It should be valve ← OPEN.