Systems: Input, Process, Output
Describe a product with an input-process-output block diagram: what enters, what happens inside the chosen system, and what leaves. Use observations and checks to narrow down possible fault locations, and explain how feedback helps control a system.
What a learner can do afterwards
- Draw a block diagram for an everyday product with the three stages labelled
- Use a block diagram and stated test evidence to identify a likely fault stage or explain what further evidence is needed
- Explain what feedback adds to a system, using a thermostat or a cruise control
- Say why the same diagram fits a kettle and a phone app
1 · Read
A block diagram models how a product works. Choose what your system includes. Draw boxes labelled input, process and output, then join them with arrows in that order. Input is what enters, such as material, energy or information. The process is what the system does. Output is the result that leaves. The diagram leaves out details that are not needed for your question.
For a kettle, water and electrical energy are inputs, heating is the process, and hot water is the output. For a phone app, taps and data are inputs, the program's work is the process, and displayed results are outputs. A toaster also needs electrical energy: bread and electricity enter, heating browns the bread, and toast is the food output.
Feedback uses information about a measured result to adjust a running system. A thermostat compares room temperature with a chosen temperature and controls the heater. Cruise control compares measured speed with the chosen speed and adjusts the car's driving force. A design iteration changes a prototype between tests; automatic feedback adjusts a system while it runs.
A symptom can have several causes. If correct input data and a clean processed signal reach a speaker, but its sound is distorted, investigate the output stage first. A diagram alone does not identify a failed component. Use supplied checks or simulations for fault tracing. Do not open mains appliances, work on live circuits or test moving vehicles. No supply at a lamp's plug means missing input, not proof of an internal lamp fault.
Label input, process and output for a chosen system. Feedback uses measured results to adjust it. Use supplied test evidence to trace possible faults safely.
Original lesson, questions and flashcards written for this dataset about system models, feedback and evidence-based fault tracing.
Original readings written for this dataset about computer and workshop tasks and the limits of system diagrams.
More to read
Model a drawing program
A user selects a colour and moves a pointer in a drawing program. These actions provide input information. The program uses that information to update a picture. The displayed picture is an output.
The processor and memory support processing, but a task diagram does not need to list every computer component.
If the picture does not update, the diagram suggests several questions. Did the input arrive? Did the program process it? Did the display show the result? The diagram organises these possibilities. Further checks are needed to distinguish them.
Model a bookmark workshop
A workshop makes bookmarks from card and ribbon. In a model focused on materials, those are the inputs. Cutting, punching and joining form the process. Completed bookmarks are the outputs. A wider model could include time and energy too.
A parts list gives the materials and quantities needed for one bookmark. It describes input requirements, not every assembly action.
If ribbons come loose, the team should investigate the materials, the joining method and handling after assembly. The visible problem alone does not establish which caused it.
Choose the limits of the model
Decide what the system includes before drawing its stages. A whole music system may have one processing box. A closer model may divide processing into several actions.
A missing electrical supply is outside a lamp when the system is the lamp alone. It explains the missing input energy, but does not prove an internal lamp fault. Use supplied evidence rather than opening an appliance.
For feedback, name the measured result and how it affects control. An extra box or a repeated output label does not by itself show that measured information changes the system's operation.
2 · Watch
Take it off screen
Where it sits
Optional connections
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.