What is a System
FoundationA system has input, process and output: input receives the command or energy, process transforms it, output is the result. Mechanical, electrical, electronic, pneumatic and computer systems can all be analysed this way.
- A system is parts working together for a specific function
- Input–process–output is the basic framework of system analysis
- The black-box method compares input and output, ignoring the inside for now
文體小知識：科技知識說明文用輸入–處理–輸出等框架解釋系統的運作，把複雜裝置化繁為簡，方便分析和學習。
§Text Passage
1Electric fans, lifts, air-conditioners, automatic doors and even the school bell are all systems. A system is a whole made of parts that work together to achieve a specific function. As long as the function is clear, any device however complex can be analysed as a system. Seeing everyday devices as systems helps you understand how they work and where to start checking when something fails.
2The commonest way to analyse a system is input–process–output, also called the black-box method. The input is the command, energy or data fed into the system; the process is the internal transformation of that input; the output is the final action or result. At first you ignore the inside, as if facing a black box, and compare the two ends. For example, for an electric kettle the input is pressing the switch and electrical energy, the process is the heating coil turning electricity into heat, and the output is boiling water.
3By the energy or signals they carry, systems can be mechanical, electrical, electronic, computer-based or pneumatic. Mechanical systems transmit motion through levers and gears, like a bicycle; electrical systems centre on electric power and motors, like a fan; electronic systems handle weak signals, like a radio; computer systems process data; pneumatic systems are driven by compressed air, like bus doors. Many products are mixed: a lift contains both mechanical and electrical parts.
4Complex systems can be broken into sub-systems, each with its own input, process and output. Some systems also have feedback: information about the output is sent back to the input so the system adjusts itself. For example, an air-conditioner's temperature sensor feeds room temperature back to the control circuit, and cooling stops once the set temperature is reached. Analysing input, process, output and feedback is the common basis for designing and repairing every technological device.
1Summary 重點摘要
A system has input, process and output: input receives the command or energy, process transforms it, output is the result. Mechanical, electrical, electronic, pneumatic and computer systems can all be analysed this way.
2Vocabulary cards Vocabulary
A whole made of parts working together for a specific function.
The command, energy or data fed into a system.
The internal change of input into output.
The action or result a system produces.
Analysing only input and output, ignoring the inside for now.
Information about the output sent back to adjust the input.
A part of a larger system with its own function.
A system transmitting force and motion through mechanisms.
A system built on electric power and motors.
A system driven by compressed air.
3Step by step Steps
- What a system isA system is a whole made of parts arranged to work together for a specific function. To decide whether a device is a system, ask whether it has a clear function and whether its parts share the work. Homes and schools are full of systems. For example, a fan must output airflow, a lift must carry people up and down, and the school bell must ring on time; each is made of many parts and circuits, and none can be missing. Recognising systems is where technological analysis begins.
- The input–process–output modelThe first framework for analysing a system is input–process–output: the input is the command, energy or data applied to the system, the process is the internal transformation, and the output is the resulting action. To write an analysis, ask what the user does, what the system finally achieves, and call the change between them the process. For example, pressing the fan switch and supplying power is the input, the motor turning electricity into blade rotation is the process, and the cool breeze is the output.
- The black-box methodThe black-box method ignores the inside of a system for the moment, treats it as a sealed box, and studies only the relationship between input and output. This makes analysing complex devices possible: fix the two ends first, then infer the inside step by step. For example, with a broken blender, test as a black box — does the blade turn when switched on? If the motor hums but the blade is still, the fault lies in the coupling; without opening the case you have narrowed the search — an engineer's usual line of thought.
- Five forms of systemsSystems are grouped by the energy or signals they carry: mechanical systems transmit motion through levers, gears and springs; electrical systems drive motors and switches with electric power; electronic systems handle weak signals; computer systems compute with data and programs; pneumatic systems push cylinders with compressed air. For example, a bicycle is mechanical, a fan electrical, a radio electronic, a smart band's step counting is computer-based, and bus doors run pneumatically. Many modern products are mixed systems with several forms together.
- Systems at home and schoolAnalysing everyday devices with input–process–output quickly builds skill. A washing machine: choosing a program and pressing start is the input; the motor, valves and heater filling, washing and rinsing according to the program is the process; clean clothes are the output. The school bell: the signal of reaching a preset time is the input, the control circuit comparing the time is the process, and the ringing is the output. For example, an automatic door senses someone approaching, the controller issues the command, and the door slides open for people carrying things.
- A first look at sub-systemsLarge systems are built from sub-systems, each with its own input, process and output, and one sub-system's output often becomes the next one's input. Breaking a big system into sub-systems makes problems solvable one at a time. For example, a lift can be split into a door sub-system, a hoisting sub-system and a control sub-system; pressing a floor button is the door control's input, the cable motor turning is the hoist's process, and opening at the floor is the output. Whatever stage fails shows which sub-system to inspect.
- Feedback and self-adjustmentSome systems send information about their output back to the input, correcting their own operation — this is feedback. With feedback, a system adjusts itself to changes without constant human help. For example, an air-conditioner's sensor keeps feeding room temperature back to the control circuit: cooling runs when the room is warmer than the setting and pauses when it is reached, keeping the room cool without wasting power. Recognising input, process, output and feedback prepares you for closed-loop control and automation design.
4Diagrams Diagrams
5Worked example Example
Example: analyse a household electric fan with a black-box diagram — write down its input, process and output, and point out which part is electrical processing.
- Input → the user presses the switch to choose a speed, and mains power supplies electricity
- Process → the control circuit adjusts the current by setting; the motor turns electricity into rotation and drives the blades
- Output → the spinning blades push the air and deliver a cool breeze
- Classification → converting electricity is electrical processing; the blades fanning air is a mechanical action
- Answer: The fan's input is the user's command (choosing a speed) together with electrical energy; the process is done by the control circuit and motor, turning electricity into blade rotation at the chosen speed; the output is the breeze produced by the blades pushing air. The part converting electricity into rotation is electrical processing, while the blades moving the air are mechanical — the fan is really a mixed electrical and mechanical system. The same framework analyses air-conditioners, blenders and other home appliances.
6Common mistakes Mistakes
7Quick check Quick check
Q1What are the three basic stages of system analysis?
Q2In an electric kettle, what is the process stage?
Q3Bus doors open and close with compressed air. Which type of system is this?
Q4What is feedback? Give one home system that has it.
Q5What is the benefit of splitting a big system into sub-systems?
8Recap Recap
- A system is parts working together for a specific function
- Input–process–output is the basic framework of system analysis
- The black-box method compares input and output, ignoring the inside for now
- Systems may be mechanical, electrical, electronic, computer-based or pneumatic
- Feedback lets systems self-adjust; big systems can be split into sub-systems