Control mechanisms: open-loop and closed-loop

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Quick Questions

Shade in the A or B circle for each question.

1. A heater runs for exactly 30 minutes and then switches off, no matter how warm the room is. Which type of control mechanism is this?

A Open loop

B Closed loop

2. A thermostat compares the room temperature with the target and switches the heater on or off. Which type of control mechanism is this?

A Closed loop

B Open loop

3. Which statement about a feedback signal is correct?

A It sends information about the result back to the control mechanism

B It tells the system to ignore the result and keep going

4. Which system is open loop?

A A sprinkler that stops when a soil moisture sensor reads wet enough

B A sprinkler that waters the garden for 10 minutes every morning

5. What does a closed-loop control mechanism have that an open-loop one does not?

A A timer that runs for a set time

B A feedback signal from the result

Match the Pairs

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

Left column		Right column
1timer.run(10)		AThis is open loop, not closed loop. It runs for a fixed time and never reads the temperature, so there is no feedback signal.
2if temp < target: heater.on()		BAn open-loop control: the heater runs for a set time and never checks the result
3A feedback signal is a measurement of the result that is sent back to the controller		Cheater.on() and wait(600) and heater.off()
4An open-loop system acts for a set time or amount and does not check the result		DA timer is open loop, but this code uses a sensor reading as feedback, which makes it closed loop.
5Thermostat (closed loop): heater.on() for 10 minutes, then heater.off()		Etemp = sensor.read()
6Timer (open loop): if sensor.read() > 25: fan.off()		FA closed-loop control: it uses the temperature reading as a feedback signal to decide what to do next

Definitions

control mechanism

Fill in the Blanks

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

heater = ON ____ 10 heater = OFF

reading = readSensor() IF reading < ______ THEN heater = ON

temp = readSensor() IF temp _ target THEN heater = ON

WHILE temp < target DO heater = ON temp = __________()

temp = readSensor() error = ______ - temp IF error > 0 THEN heater = ON

Spot the Error

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

Question 1

A # Open loop: thermostat

B while True:

C temp = read_sensor()

D if temp < 20: heater_on()

Question 2

A timer = 600

B pump_on()

C sleep(timer)

D pump_on()

Question 3

A target = 22

B temp = target

C if temp < target:

D heater_on()

Question 4

A temp = read_sensor()

B if temp > 20:

C heater_on()

D else:

E heater_off()

Question 5

A target = 22

B temp = read_sensor()

C error = target - temp

D adjust(target)

Answer Key

Control mechanisms: open-loop and closed-loop

Section A: Quick Questions

A — Open loop

A — Closed loop

A — It sends information about the result back to the control mechanism

B — A sprinkler that waters the garden for 10 minutes every morning

B — A feedback signal from the result

Section B: Match the Pairs

timer.run(10) → An open-loop control: the heater runs for a set time and never checks the result

if temp < target: heater.on() → A closed-loop control: it uses the temperature reading as a feedback signal to decide what to do next

A feedback signal is a measurement of the result that is sent back to the controller → temp = sensor.read()

An open-loop system acts for a set time or amount and does not check the result → heater.on() and wait(600) and heater.off()

Thermostat (closed loop): heater.on() for 10 minutes, then heater.off() → This is open loop, not closed loop. It runs for a fixed time and never reads the temperature, so there is no feedback signal.

Timer (open loop): if sensor.read() > 25: fan.off() → A timer is open loop, but this code uses a sensor reading as feedback, which makes it closed loop.

Section C: Definitions

control mechanism — Decides what a system does next. Open loop ignores the result (a timer); closed loop uses a feedback signal from the result (a thermostat).

Section D: Fill in the Blanks

heater = ON
WAIT 10
heater = OFF

reading = readSensor()
IF reading < target THEN
  heater = ON

temp = readSensor()
IF temp < target THEN
  heater = ON

WHILE temp < target DO
  heater = ON
  temp = readSensor()

temp = readSensor()
error = target - temp
IF error > 0 THEN heater = ON

Section E: Spot the Error

A — A thermostat reads the temperature with a sensor and uses it to decide what to do, so it is a closed loop. The comment should say 'Closed loop: thermostat'.

D — An open-loop timer switches the pump on, waits, then switches it off. Line 4 repeats pump_on(), so the pump never stops. It should be pump_off().

B — A closed loop needs a feedback signal from the real world. Setting temp to target means the heater never sees the actual temperature. It should be temp = read_sensor().

B — The thermostat should turn the heater on when the feedback shows the room is too cold. The test should be temp < 20, not temp > 20.

D — In a closed loop the adjustment uses the feedback (the error between target and measured value). Passing only target ignores the result. It should be adjust(error).