Input, process, output

A control system follows the input to process to output pattern:

• Input — sensors measure the physical world (temperature, light, pressure, motion).
• Process — a microprocessor compares readings against target values and decides what to do.
• Output — actuators (motors, heaters, valves) change the physical world.

Sensors, transducers and actuators

A sensor detects a physical quantity; a transducer converts one form of energy into another (for example a physical quantity into an electrical signal). An actuator converts a control signal into physical action, such as a motor turning or a valve opening.

Role of a sensor

Role of an actuator

Input, output or control?

Tap a component, then the part of the control system it belongs to.

Open and closed loops

Control can be open loop or closed loop:

• Open loop — no feedback; the system does a fixed action regardless of the result (a simple timer).
• Closed loop — uses feedback: the output is measured and fed back so the system self-corrects (a thermostat that switches the heater off when the target temperature is reached).

Feedback loop

Centralised and distributed control

In centralised control one processor makes all the decisions — simple, but a single point of failure. In distributed control, many processors cooperate — more robust and scalable, but harder to coordinate. Autonomous agents (robots, self-driving vehicles) sense and act on their own within their environment.

Distributed control

Real-world control systems

Everyday control systems include traffic lights, central heating, washing machines, automatic doors, lifts, irrigation and GPS navigation. Large industrial plants use SCADA to supervise and control processes over a wide area. Each has social and ethical implications for safety and reliability.

Match the system to its sensor

Tap a control system on the left, then the sensor it relies on.

Microprocessors and microcontrollers

A microprocessor is a general-purpose CPU on a chip. A microcontroller combines a processor, memory and input/output on a single chip, designed for one embedded control task — cheap, low-power and reliable, which is why they run washing machines, cars and appliances.

Microcontroller

Social and ethical impacts

Automated control systems raise safety and reliability concerns: a fault in a medical, aircraft or traffic system can be dangerous, so they need thorough testing, fail-safes and redundancy. There are also impacts on employment and on privacy where sensors collect data.

Safety-critical

The big ideas to know

You have covered the key ideas in Topic 7 — control. Press Finish to see your score.