Whole Revision Guide Part 2 Flashcards
How are PCBs made consistent?
keep exposure time the dame so that the same amount of copper is removed from the board
What are reference points?
a point where measurements are made from
they help control accuracy
they are important in aligning CAM machines and when scaling the size of something
name 3 production aids
templates, patterns, jigs and reference points
what do jigs do?
guides tools, can be specifically made for a job, they speed up production and simplify the making process
what are short length and long length fibres called?
staple and filament
What are the three categories for fibres
natural, regenerated, synthetic
what are regenerated fibres?
natural fibres that have been chemically treated
like viscose fibres
how are viscose fibres made?
cellulose is dissolved in sodium hydroxide solution. the liquid is forced through tiny holes and hardened to form filament fibres. filaments are stretched into yarns
what is steel often used for?
vehicle parts, like brake disks, engine, wheels and drive shaft. durable vehicle parts can be made relatively cheaply and easily. car bodies are also made from steel as they are designed to crumple and absorb impact
what is aluminium used for in motor vehicles
corrosion resistant car body parts instead of steel. it’s less dense so improves acceleration and fuel economy. it’s more expensive
Why are electrically conductive strips used in cars?
they are on the inside of the rear window to defog it and clear the glass by heating up
what conditions do engine electronics need to withstand?
high temperatures and freezing conditions
what does a drive belt do in a washing machine?
transmits rotary motion to the spinning drum. they are often made from rubber or a polyurethane plastic because they are strong and flexible
what is a heating element?
a wire that gets hot when a current passes through it, caused by electrical resistance. often made from a nickel-chromium alloy as it has a high melting point
what do photosensitive materials do?
respond to being exposed to light, like photographic film and light dependent resistors. photoetching is used to etch designs onto PCBs
how is aluminium oxide different to rust?
it sticks strongly to the fresh aluminium and protects it from further corrosion.
what is anodisation?
anodisation thickens the protective oxide using electric current. anodised aluminium is used to make aircraft parts, pans and window frames
what do current and voltage ratings do?
prevent damage to components by informing the user what current and voltage the appliance is supposed to work at.
what do resistors do?
they reduce the current in a circuit. a greater resistance than needed is safer
what do bands 1 and 2 on a resistor indicate?
the first two digits of the resistance
what does band 3 on a resistor do?
indicates how many zeroes that come after the first two digits
what does band 4 on a resistor do?
represents the tolerance. an E12 resistor will have a silver band 4, representing 10% tolerance
what is a Dual In Line package?
one of the ways ICs are packaged. the circuit is placed in a rectangular protective casing made of plastic/ ceramic. metal legs stick out of the casing in two parallel rows.
How can ICs be attached to a circuit?
soldered through hole, or plugged into an IC socket making them easier to replace
what is a PIC?
a specific type of microcontroller. they are programmable intelligent computers. most have flash memory. different PICs have different amounts of memory and pins.
what are chains and what do they do?
roller chains are metal links pinned together to form a loop. they transfer rotary motion from one sprocket to another
what are gears and what do they do?
they can have different number of teeth and tooth shapes
what are the two types of spring you can buy?
compression (resist compression), and extension (resist extension)
what is spring rate?
how easy the spring is to stretch or compress
What does CNC stand for?
computer numeric control. CAM machines use this and involves using the precise coordinates to control where the laser cuts
what do PCB drills do?
cut holes in PCBs so that pins or wires can be pushed through. very thin drill bits are used.
How is soldering done in mass production?
flow soldering. this is when the PCB is passed over a pan of molten solder. A pump produces an upwelling to solder in place.
