Automated Systems

Every automated system, no matter how simple or complex, is built from the same three kinds of part:

The pipeline

The three components form a clear input-process-output pipeline:

Sensor → Microprocessor → Actuator

1. The sensor measures the relevant physical quantity (e.g. temperature) and sends a digital reading to the microprocessor.
2. The microprocessor compares the reading against the rules in its program (e.g. "if temperature < 20 °C, switch on heater") and decides what to do.
3. If action is needed, the microprocessor sends a control signal to an actuator, which performs the physical change (e.g. turns on the heater motor or opens a valve).

Many sensor types appeared in topic 8 (Input and Output Devices); each one of those sensors can be the input side of an automated system. Common actuators include motors, servos, valves, relays, heaters, pumps, alarms and buzzers.

A small worked walkthrough

Example — A central-heating thermostat with a target of 20 °C.

1. The temperature sensor reads the current air temperature, e.g. 18.5 °C, and sends the value to the microprocessor.
2. The microprocessor compares the reading to the target (20 °C). Since 18.5 < 20, the room is too cold.
3. The microprocessor sends a signal to the actuator (a relay controlling the boiler), which switches on the boiler.
4. The boiler heats the radiators; the room temperature rises.
5. The sensor keeps reading. When it sends 20.1 °C back, the microprocessor decides the room is warm enough and sends a different signal to the relay to switch off the boiler.
6. The cycle repeats, keeping the room within a small band around the target temperature.