The three parts of an automated system
An automated system is a mix of hardware and software that does a job without a person controlling it.
A sensor is an input device that measures something physical, such as temperature or light, and sends the reading as data.
A microprocessor is the processor on a single chip. It compares the sensor reading with a stored set value (the target) and decides what to do.
An actuator is an output device that makes something move or switch, such as a motor, a valve, a heater or a pump.
?Why?Most sensors give an analogue signal (a smooth range of values). A microprocessor only works with digital data, so an analogue-to-digital converter (ADC) changes the reading first. Some actuators need a DAC to turn the output back into analogue.
!Watch outA sensor does not decide anything. It only measures. The microprocessor makes the decision.
The control loop, step by step
An automated system runs a loop. It keeps checking and correcting, all day, without stopping.
Use the greenhouse toy. Drag the temperature reading, or change the set values (heater on below, window opens above). Press Run one loop and watch the microprocessor compare them and switch the actuators on or off.
To match the example below, set Window opens above to 24 and drag the temperature to 27.
In the exam, write the steps in this order: sensor reads, ADC converts, microprocessor compares with the set value, actuator acts, the loop repeats.
e.g.ExampleGreenhouse with a set temperature of 24 °C.
1. The temperature sensor measures the air: 27 °C.
2. The reading is converted from analogue to digital by an ADC.
3. The microprocessor compares 27 with the set value of 24.
4. 27 is higher than 24, so it sends a signal to the actuator.
5. A motor opens the window (and the heater is switched off).
6. The system loops back to step 1 and keeps checking.
7. When the reading falls to 24 °C, the microprocessor closes the window.
?Why?The loop is what makes the system automatic. Every new reading can change the action, so the conditions stay close to the target.
!Watch outDo not write "the sensor opens the window" or "the sensor decides it is too hot". Sensors only send readings.
There is something to try for this step in the IGCSE library.
Scenarios: industry and transport
In industry, automated systems control production lines, chemical plants and power stations.
In transport, they control trains, traffic lights and parts of cars, and they are the basis of self-driving vehicles.
Scenarios: agriculture and weather
In agriculture, automated systems water crops, feed animals and control greenhouses.
In weather monitoring, automated stations take readings day and night in remote places.
Scenarios: gaming, lighting and science
In gaming, sensors in controllers and headsets turn movement into actions in the game.
In lighting, light and infra-red sensors switch lights on and off by themselves.
In science, automated systems run experiments and take readings for long periods.
Advantages and disadvantages in general
Many exam questions ask you to evaluate an automated system. Use these general points, but always link them to the scenario in the question.
!Watch outGeneral answers such as "it is cheaper" score poorly. Say what is saved and why, for example "the irrigation system saves water because it only opens the valve when the soil is dry".