Systems Approach - Inputs Processes and Outputs
Systems Approach — Inputs, Processes and Outputs
The systems approach is a way of analysing how products and processes work by breaking them into three stages: input, process, and output. AQA expects you to apply this thinking to mechanical, electronic, and manufacturing systems.
The Basic Systems Model
Every system follows the same fundamental structure:
INPUT → PROCESS → OUTPUT
- Input: The energy, material, or signal that enters the system
- Process: The action or transformation that takes place
- Output: The result — the product, movement, signal, or energy that leaves the system
Feedback and Control
Many systems include feedback, where part of the output is fed back to the input to regulate the system. This creates a closed-loop system.
| System Type | Description | Example |
|---|---|---|
| Open-loop | No feedback — output is not monitored or adjusted | A toaster (runs for set time regardless of toast colour) |
| Closed-loop | Has feedback — output is measured and used to adjust the input | A thermostat-controlled central heating system |
In a closed-loop system:
1. A sensor detects the current output (e.g. temperature sensor)
2. A comparator compares the measured value to the desired value (set point)
3. If there is an error (difference), the system adjusts the input
4. The process continues until the output matches the set point
Sub-Systems
Complex systems are often broken into sub-systems — smaller functional blocks that each perform part of the overall task. This makes systems easier to design, test, and repair.
For example, a washing machine has sub-systems for:
- Water intake (input: mains water → process: valve opens → output: drum fills)
- Heating (input: electricity → process: element heats water → output: warm water)
- Agitation (input: motor power → process: drum rotates → output: clothes agitated)
- Drainage (input: pump power → process: pump activates → output: water removed)
Applying Systems Thinking to Products
| Product | Input | Process | Output |
|---|---|---|---|
| Electric drill | Electricity (mains/battery) | Motor converts electrical to rotational energy | Drill bit rotates |
| Torch | Chemical energy (battery) | Circuit converts chemical to electrical energy | Light emitted (LED/bulb) |
| Wind turbine | Kinetic energy (wind) | Turbine and generator convert kinetic to electrical | Electricity |
| Sewing machine | Electrical energy + fabric | Motor drives needle mechanism | Stitched fabric |
| 3D printer | Electrical energy + filament + digital file | Heater melts filament, motors position head | 3D printed object |
Systems in Manufacturing
Manufacturing processes can also be modelled as systems:
- Input: Raw materials, energy, labour, design specifications
- Process: Cutting, shaping, joining, finishing
- Output: Finished product, waste material, heat
Quality control acts as feedback in manufacturing — if products fail inspection (output), the process is adjusted (e.g. recalibrating a machine).
Electronic Systems
Electronic products are systems with specific input, process, and output components:
| Stage | Components |
|---|---|
| Input (sensors/switches) | LDR, thermistor, microphone, switch, potentiometer |
| Process (decision/control) | Microcontroller, transistor, timer (555), comparator |
| Output (actuators) | LED, motor, buzzer, speaker, solenoid, heater |
A typical electronic system: LDR (input) → microcontroller (process) → LED (output) — an automatic night light.
Flowcharts for System Processes
Systems can be represented as flowcharts using standard symbols:
- Oval/rounded rectangle — start/end
- Rectangle — process step
- Diamond — decision (yes/no)
- Parallelogram — input/output
- Arrow — flow direction
Flowcharts are particularly useful for describing programmable systems (e.g. microcontroller logic) and manufacturing sequences.
Exam Tips
- When asked to draw a systems diagram, always use the three boxes with labelled arrows: Input → Process → Output
- If the question mentions a sensor or automatic adjustment, it is asking about a closed-loop system — include the feedback loop in your diagram
- Practice identifying inputs, processes, and outputs for everyday products — kettles, automatic doors, security lights
- For electronic systems questions, name specific components at each stage rather than generic descriptions
- When describing feedback, explain what is measured, what it is compared to, and how the system adjusts
Key Definitions
- System: A set of interconnected components that work together to perform a function
- Feedback: Information about the output that is used to adjust the input or process
- Closed-loop system: A system that uses feedback to automatically control its output
- Open-loop system: A system with no feedback — the output is not monitored
- Sub-system: A smaller system within a larger system, performing a specific function