Key term
CCEA A-Level Technology and Design 8900
Material Selection and Wood
Metals
Plastics
Composite and Emerging Materials
Processing Materials
Product Analysis and Design Communication
Design for Manufacture, Quality and Safety
Electronic Control SystemsOption A
Topic overviewControl systems, feedback and electronics safetyResistors, Ohm's law and power ratingsCapacitors and RC timingPotential dividers, sensors and comparatorsSwitches, pull-up and pull-down resistorsOutput devices and LEDsTransistors, Darlington pairs and thyristorsLogic gates, truth tables and flip-flops555 monostable and astable timers
Microelectronic Control SystemsOption A
Topic overviewMicrocontroller systems, ADCs and DACsStrain gauges and bridge circuitsOptical switches, encoded discs and Schmitt triggersOp-amp amplifiers and gainZener diodes and voltage regulatorsKarnaugh maps and binary countersSeven-segment, LCD and dot matrix displaysPIC flowcharts and programmingDC motors, stepper motors and driver circuits
Mechanical and Pneumatic ComponentsOption B
Topic overviewOpen and closed loop mechanical and pneumatic controlSafe working with compressed air and mechanismsLevers, linkages and momentsGear types and gear trainsPulleys, belts, chains and shaft fixingsCams, cranks and converting motionCompressed air supply and pneumatic valvesCylinders, shuttle valves, restrictors and reservoirsPneumatic circuits for logic, timing and speed control
Mechanical and Pneumatic SystemsOption B
Topic overviewHydraulics, system limitations and plant safetyTorque, work, power and air consumptionVacuum handling, proximity sensors and 5/3 valvesSequential and cascade pneumatic circuitsCam profiles and follower displacement diagramsGear geometry, pulley blocks and ratchetsToggles, treadles, shafts and couplingsFriction, brakes and clutchesBearings, lubrication and seals
Designing and Manufacturing ProductsOption C
Topic overviewResearch, questionnaires and specificationsIdea generation, critiques and computer simulationManufacturing planning and product evaluationCFRP, GRP, Kevlar and tungsten carbideSmart materials, nanotechnology and biophotovoltaicsIsometric, perspective and assembly drawingLaminating, steam bending, cutting and printing processesRisk assessment and product safety lawScales of production, JIT and cell productionQuality assurance, ISO 9001 and continuous improvementDesign influences and intellectual property rights
Product Design in Industry and SocietyOption C
Topic overviewLife-cycle environmental impact and climate changeThe 6Rs, waste and environmental legislationSustainable metals, plastics and degradable polymersProduct life cycles, consumer types and relaunchesCAD, CAM, 3D scanning and quick-change mouldingMarket pull, technology push and market strategyPrice, place and promotionJigs, fixtures and ICT in quality controlDesign for maintenance, inclusion and scale productionRendering, typography and presentationDyson, Baylis, Memphis and Apple
Product Development
Product and System Design and Manufacture
Mechanical and Pneumatic Systems
Sequential and cascade pneumatic circuits
- 3 things to know
- A2 1
Overview
Sequence notation, feedback in sequential circuits, signal conflict and one-way trip valves, the cascade method and grouping rules with worked sequences, and programmable logic controllers.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Process
How is a cylinder sequence written in notation?
Key term
What is meant by positive feedback in a pneumatic sequential circuit?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a sequential pneumatic circuit?
Model answer
A sequential circuit makes several cylinders move one after another in a set order. Each movement starts only when the one before has finished.
- 2
How is a cylinder sequence written in notation?
Model answer
Each cylinder is given a letter, with + for extending and − for retracting. A+ B+ A− B− means A extends, B extends, A retracts, then B retracts.
- 3
What is meant by positive feedback in a pneumatic sequential circuit?
Model answer
Each cylinder operates a limit valve when it completes its movement. The limit valve's signal confirms the movement and starts the next one.
- 4
In the sequence A+ B+ A− B−, which signal starts B+?
Model answer
B+ is started by the limit valve at the fully extended end of cylinder A's stroke. Cylinder B therefore moves only once A is known to be out.
- 5
What is signal conflict in a sequential circuit?
Model answer
Signal conflict occurs when both pilot ports of a 5/2 valve receive a signal at once. The valve cannot change over, so the sequence stalls.
- 6
Explain why the sequence A+ B+ B− A− suffers signal conflict with simple limit valves.
Model answer
The limit valve held down by cylinder A when extended keeps signalling B+. Cylinder B's 5/2 valve then receives the B+ and B− signals together.
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