The shape of the lesson
By the end of the lesson, learners can
- Sense, decide, act: Every automated system in an exam answer works the same way.
- Automation everywhere: The syllabus names seven areas.
- Worth automating?: Exam questions give a scenario and ask for advantages and disadvantages.
- Sensor: measures and sends data (via an ADC if analogue) to the microprocessor.
- Microprocessor: compares the data with stored values and decides.
- Actuator: receives a signal and physically acts (motor, pump, valve, heater).
- Repeat: say the process is continuous, and apply advantages and disadvantages to the scenario.
One picture every idea returns to
An automated system carries out a task with little or no human input. A sensor measures a physical quantity (such as temperature or light) and sends data to a microprocessor. The microprocessor compares the data with stored values (a set point or range) and decides what to do. If action is needed it sends a signal to an actuator (such as a motor, valve, heater or pump), which changes the environment. The sensor keeps taking readings, so the process repeats continuously.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Systems that run themselves.. Street lights that switch on at dusk, a greenhouse that waters itself, a train with no driver: each one senses the world, decides what to do and acts, over and over, without a person in the loop. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Sense, decide, act | Every automated system in an exam answer works the same way. Model the worked example Automatic greenhouse on the board, one line at a time. Your turn: An automatic door at a shop uses an infrared sensor. Name the actuator and say what the microprocessor checks. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Automation everywhere | The syllabus names seven areas. Your turn: An automated street light uses a light sensor. Describe what happens at dusk. | Pairs |
| 21 to 30 min | Teach and check: Worth automating? | Exam questions give a scenario and ask for advantages and disadvantages. Model the worked example Apply it on the board, one line at a time. | Anticipation / Reaction Guide |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 21 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Worth automating?, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Anticipation / Reaction Guide
Before the lesson, students mark five statements true or false. After the teaching they mark them again and justify any change of mind in one sentence each. The statements come from the examiner traps below.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| "The sensor turns on the heater" earns nothing. | Sensors only measure and send data; the microprocessor makes the decision and the actuator does the action. |
| Name the right sensor for the scenario. | A greenhouse that waters plants needs a moisture sensor; a temperature sensor alone cannot tell if the soil is dry. |
| "It is more efficient" on its own is too vague to earn a mark. | Say what is better, e.g. "it responds to a pressure rise faster than a human operator could". |
Automated systems: sensors, microprocessors and actuators: worksheet
6 questions, 21 marks. Written in the style of the papers; no past paper question is reproduced.
State the purpose of each of these in an automated system: (a) a sensor, (b) a microprocessor, (c) an actuator.
A museum keeps the humidity of a display room between 45% and 55% to protect old paintings. It uses a humidity sensor, a microprocessor, a humidifier and a dehumidifier. Describe how the system keeps the humidity in this range.
Name one suitable sensor and one suitable actuator for an automatic system that turns on a fan in a school kitchen when the air becomes too smoky.
A city plans to replace train drivers with a fully automated (driverless) train system. Give two advantages and two disadvantages of this.
A game console controller contains a gyroscope and a vibration motor. Explain how they are used together with the console's microprocessor during a racing game.
A school laboratory uses an automated system to record the temperature of a reaction every 10 seconds for one hour. Give three advantages of using this system instead of a student taking readings.
Answer key and marking notes
- (a) A sensor measures a physical property (e.g. temperature) and sends the data to the microprocessor.
- (b) A microprocessor processes the data: it compares it with stored values and decides what action to take.
- (c) An actuator receives a signal from the microprocessor and performs a physical action, e.g. a motor turning or a valve opening.
- The humidity sensor measures the humidity of the room and sends the data to the microprocessor (via an ADC).
- The microprocessor compares the reading with the stored range of 45% to 55%.
- If the humidity is below 45%, the microprocessor sends a signal to switch the humidifier on (and the dehumidifier off).
- If the humidity is above 55%, it sends a signal to switch the dehumidifier on (and the humidifier off).
- If the reading is within the range, both are switched off (or left off).
- The sensor keeps taking readings, so the process repeats continuously.
- Sensor: gas / smoke sensor.
- Actuator: a motor that drives the fan (extractor fan).
- Advantage: trains can run closer together and more frequently because the system responds faster than a human driver.
- Advantage: no driver errors from tiredness or distraction, and lower wage costs over time (accept: more consistent braking saves energy).
- Disadvantage: very expensive to install sensors, control systems and platform doors.
- Disadvantage: a hacker or a software/sensor fault could stop trains or cause an accident; drivers lose their jobs.
- The gyroscope (sensor) detects how the player tilts the controller and sends the data to the microprocessor.
- The microprocessor uses the data to steer the car in the game, and decides when the car hits something.
- It then sends a signal to the vibration motor (actuator) so the player feels the crash through the controller.
- Readings are taken at exactly the right times, so the results are more accurate and consistent.
- It can take readings over a long time without getting tired or losing concentration (and could run overnight).
- The student does not need to stay near a possibly dangerous reaction; the data is stored automatically and can be graphed straight away.
6 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
In an automated system, what is the job of an actuator?
- ATo physically move or change something when it receives a signal
- BTo measure a physical quantity such as temperature or light
- CTo compare readings with stored values and decide what to do
- DTo convert analogue signals into digital data
A farm uses an automated system to water crops only when the soil is too dry. Which sensor and actuator are most suitable?
- AMoisture sensor and water pump
- BLight sensor and water pump
- CMoisture sensor and heater
- DInfrared sensor and motorised gate
Why is an analogue-to-digital converter (ADC) often placed between a sensor and a microprocessor?
- ASensors often give analogue signals; microprocessors need digital data
- BThe microprocessor produces analogue signals that the sensor cannot understand
- CThe ADC stores the set point that the readings are compared with
- DThe ADC switches the actuator on when a reading is too high
Which is a disadvantage of using an automated system to control the traffic lights at a busy junction?
- AA faulty sensor could cause the lights to change at the wrong time
- BIt can respond to the traffic faster than a human operator
- CIt can run 24 hours a day without needing breaks
- DNo person has to stand in the road to direct traffic
An automated greenhouse switches its heater ON when the temperature is below 20 °C and OFF when it is above 25 °C; between these values the heater stays as it is. The heater starts OFF. The sensor gives the readings 22, 19, 21, 24, 26, 23 (°C). What is the state of the heater after the last reading?
- AOFF
- BON
- CON, then OFF again at 23 °C
- DOFF, because 23 °C is below 25 °C
An automated street light has switched its lamp on at dusk. Why does the system keep reading the light sensor afterwards?
- ASo it can detect daylight and switch the lamp off
- BBecause the lamp needs a sensor reading to stay lit
- CSo the sensor can switch the lamp off by itself at dawn
- DBecause the set point changes every time a reading is taken
Quiz key
An actuator is an output device, such as a motor, pump, valve or heater, that carries out a physical action when the microprocessor signals it. Measuring a physical quantity is the sensor's job. Comparing with stored values and deciding is the microprocessor's job. Converting analogue to digital is done by an analogue-to-digital converter (ADC).
A moisture sensor measures how wet the soil is, and a pump (or valve) is the actuator that supplies the water. A light sensor cannot tell whether the soil is dry. A heater would not water the crops. An infrared sensor detects movement or heat, and a gate does not deliver water.
Most sensors give a continuously varying (analogue) signal, and the microprocessor only works with digital data, so the ADC converts it. The microprocessor sends signals to actuators, not analogue signals to sensors. Set points are stored in memory and used by the microprocessor. Switching the actuator is triggered by the microprocessor, not the ADC.
If a sensor or the software fails, the system may take the wrong action, which could be dangerous at a junction. Responding faster than a human, working 24/7 and keeping people safely out of the road are all advantages of automation, not disadvantages.
22: within range, stays OFF. 19: below 20, switched ON. 21 and 24: within range, stays ON. 26: above 25, switched OFF. 23: within range, stays OFF. So the heater is OFF. Answering ON ignores the 26 °C reading. 23 °C is inside the range, so it does not cause a change. 'Below 25 °C' is not a reason to switch OFF: the heater stays OFF only because it was already switched off at 26 °C.
The process repeats continuously: the microprocessor keeps comparing new readings with the stored value, so when the light level rises above it at dawn it signals the lamp to switch off. The lamp stays lit until it is told otherwise; it does not need constant readings. The sensor only measures; the microprocessor decides and signals the actuator. The stored set point does not change with each reading.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.