Learning Objectives
- Define an automated system and distinguish it from a system that requires continuous human control.
- Describe how input, processing, output and feedback form a control cycle.
- Explain how sensors, a microprocessor and actuators collaborate in an automated system.
- Apply the control-cycle model to unfamiliar examination scenarios.
Key Terms
- Automated system
- A system that carries out a process using programmed control with little or no continuous human intervention.
- Sensor
- An input device that measures a physical property in the environment and supplies data to a computer system.
- Microprocessor
- A programmable processing device that receives input data, applies stored instructions or rules and produces control signals.
- Actuator
- An output device that causes a physical change, such as moving a mechanism, switching a device or opening a valve.
- Control cycle
- The repeated sequence of sensing, processing, acting and checking the changed conditions.
- Feedback
- Data about the result of an action that is returned to the controller so that the next decision can be made.
- Set value
- The desired value or condition that an automated system attempts to maintain.
What Makes A System Automated
An automated system uses a computer-based controller to perform a task or maintain a condition without a person making every individual decision. A human may start the system, enter a target value or supervise its operation, but the repeated control decisions are made automatically from input data and programmed instructions.
Automation is not the same as simply using an electrical machine. A basic electric fan switched on by a person is powered, but it is not necessarily automated. A temperature-controlled fan that uses a sensor to measure room temperature, compares the reading with a set value and changes its speed automatically is an automated system.
The central idea is a loop. The system measures what is happening, processes the measurement, takes an action and then measures again. Repeating this cycle allows the system to respond when conditions change.
The Four Main Stages
The stages are connected. A sensor on its own can measure a value but cannot decide what to do. A microprocessor can apply rules but needs current input data. An actuator can create a physical action but needs a control signal. An automated system works because all three components collaborate.
| Stage | Purpose | Typical Example |
|---|---|---|
| Input | Collect data about a physical condition | A temperature sensor measures the air temperature |
| Processing | Compare the data with rules, limits or a desired value | The microprocessor checks whether the temperature is above the set value |
| Output | Send a control signal that causes a physical response | An actuator switches on a cooling fan |
| Feedback | Measure the new condition and repeat the decision | The sensor continues measuring until cooling is no longer required |
A Complete Example: Temperature Control
Consider a greenhouse in which the desired temperature is 24 degrees Celsius. A temperature sensor repeatedly measures the air. The reading is sent to a microprocessor. The program compares the reading with 24. If the temperature is too high, the controller sends a signal to an actuator that opens a vent or starts a fan. If the temperature is too low, it may switch on a heater.
After the actuator changes the environment, the sensor takes another reading. The new reading becomes feedback. The controller does not assume that one action has solved the problem; it continues to monitor the environment and adjusts the output when required.
Good examination answers explain the sequence in context. It is not enough to list “sensor, processor, actuator.” The answer should state what the sensor measures, what comparison or rule is applied and what physical change the actuator makes.
Continuous Monitoring And Discrete Events
Some automated systems monitor a value continuously or at frequent time intervals. Temperature, light intensity, soil moisture and pressure are common examples. The controller repeatedly checks whether the value is inside an acceptable range.
Other systems respond to events. A door sensor may report that a door has opened, a proximity sensor may detect an object, or a pressure pad may detect that someone is present. The controller then follows a programmed response. Both kinds still use the same input-process-output principle.
Human Involvement
Automation reduces continuous human involvement, but it does not remove people completely. People design and program the system, choose suitable sensors and actuators, set target values, maintain equipment and deal with faults. In safety-critical situations, a human override or emergency stop may also be provided.
A system can therefore be highly automated while still requiring human supervision. The important distinction is that routine control decisions are made by the programmed system rather than by a person performing every step.
Worked Examples
Automatic Street Lighting
Question: Explain how an automatic street-light system can switch lights on when it becomes dark.
- A light sensor measures the light intensity.
- The sensor data is sent to a microprocessor.
- The program compares the reading with a stored threshold.
- If the reading is below the threshold, the microprocessor sends a signal to an actuator or switching circuit.
- The lights are switched on, and the sensor continues to provide feedback.
Answer: The system repeatedly senses light intensity, processes the reading and controls the lights without a person operating each switch.
Identifying The Missing Component
Question: A moisture sensor sends readings to a microprocessor, which decides that a field is too dry. What additional component is needed to water the field automatically?
- The sensor has provided input.
- The microprocessor has made the decision.
- A physical action must now be produced.
Answer: An actuator is required, for example an electrically controlled valve or pump that starts the irrigation system.
Examination Guidance
- Name the physical quantity measured by the sensor in the given scenario.
- State the decision made by the microprocessor, including the threshold or target when one is provided.
- Describe the physical action produced by the actuator.
- Use feedback to show that the process repeats after the output changes the environment.
- Do not describe a sensor as producing the physical output; that is the role of an actuator.
Common Mistakes
- Calling every electric or computer-controlled device an automated system without explaining automatic decision-making.
- Writing a list of components without describing the flow of data and control signals.
- Saying that the microprocessor directly opens a valve or moves a motor; it sends a signal to an actuator.
- Forgetting that the sensor takes further readings after the action.
Knowledge Check
1. What is an automated system?
2. What is the role of feedback?
3. Why is a microprocessor needed?
4. Give one example of an actuator.
5. Why is a manually switched electric heater not necessarily automated?
