Testing circuits and electrical safety Flashcards
Health and Safety
PAT testing
Portable appliance testing is the routing (usually annualy) testing of portable appliances (no shocks there then)
Basically anything that can be moved and plugged in needs to be tested and a sticker or sign added to show it has passed (or not)
Often test equipment is used to automatically test the insulation of the cables, polarity of the wiring, that equipment is correctly earthed and the correct fuses are used.
The 4 ‘R’s
REDUCE
In designing and making we should be aiming to reduce certain aspects to improve the sustainability of our products
- reduce the amount of material we use - can we redesign the packaging to use less material - less waste is thrown away or rethink the layout of parts on a sheet of wood so less waste bits go in the bin
- reduce the amount of energy used to manufacture the product - insulating the factory would mean less is wasted or using more efficient machines that waste less energy
- reduce the amount of energy the product uses - ‘low energy’ light bulbs waste less energy than previous types or auto-turn off features would waste less energy
Test methods
Expected values
A very reliable method of testing is to compare readings with expected values
You did this when you used the oscilloscope to check your circuits matched the exepcted values in the original question
This could be expected voltages, times, currenmts, temperatures etc etc
Another method is the use of ‘truth tables’ .e.g.
the boiler should be on when
there is gas available
there is water in the tank
the pump is working
the room is cold
Renewable sources of energy
WIND ENERGY
Usually uses a turbine (like a windmill) which has a set of blades that turn in the wind, which turn a generator which makes electricity.
Two main areas of use
- individually - either large ones ina field on their own or even smaller ones mounted to the roof of a house
- in ‘wind farms’ large collections of turbines, sometimes out at sea
Some advantages
- Energy is free once turbine has been purchased and installed (some maintenance and repair is needed)
- Wind will never run out like coal or oil will
- Create no pollution in electricity production e.g. greenhouse gases (you might discuss noise or visual polution though)
- Land underneath can still be used - often combined with solar panels in suitable countries
- Could provide an energy source for very remote locations not on the national grid (islands)
Some disadvantages
- The wind does not always blow and can get weaker or stronger - the output is variable and unreliable
- Not always liked by people nearby - ruins the view, noisy, might hurt birds
- Often need to be placed in quite difficult to get to places - hills, sea etc
- Can’t supply enough of our energy needs on their own
- They use lots of energy whilst being made and transported to where they are going to be used
Here is a videoof some advantages and disadvantages
Development of wind turbines is progressing rapidly.
Here is a website that lists some recent developments - read some so you can say in an exam “for example…”
Test methods
Visual inspection
Without doubt the most efficient methos of finding faults is to actually look for them!
Having a ‘good’ version to compare the item being tested against makes things more reliable
Using light boxes to make holes (where missing components should be) show up clearly is a variation
Test methods
Half split
As it’s name suggest this means dividing something in half to speed up the finding of a fault.
For instance if you were testing the continuity of a circuit track and had found there was a fault but didn’t know where it was you would
test the first half - no fault
test the second half for confirmation - fault found
test the first half of the faulty part - fault found
Split this in half again to very quickly narrow dowm where the fault lies.
Test equipment
Multimeter
The most common form of test equipment available.
Common ones can measure resistance, voltage (AC & DC), current and check continuity
More complex types can test the operation of transistors, measure capacitance and measure temperatures
Some types you have to set the correct range yourself whilst others are ‘autoranging’
Health & Safety
Visual inspection of equipment
There should be routine (every month or week etc) inspections of electrical equipment used in industry.
In a visual inspection they will be looking for:
- Damage to cables such as burns or cuts
- Evidence of ‘sparking’ such as burn and scorch marks
- Fraying cables
- Cables no longer help by strain relief clamps etc
- Loose connectors
- Loose or damaged access panels to circuit connections
Test equipment
Signal generators
These are usually used with oscilloscopes (see another card)
They can ‘make’ signals such as that which might come from a microphone and are used for testing amplifiers or speakers.
They can make signals that go on-off repeatedly to test other electronic circuits such as counters
They can make random ‘noise’ to test that circuits such as internet connections can filter it out
They can be real pieces of equipment but are also available in circuit simulation software such as Circuit Wizard
Test equipment
Logic probe
In some ciruits, such as computer circuits, where all of the voltages are going to be either 5V or 0V (called digital circuits) we don’t need the complexity of a multimeter and sometimes a simple logic probe is all that is needed
These make an LED light and a high note sound for HIGH (5V)
They make a different LED light and sound a low note for LOW (0V)
Health and Safety
RCDs
RCD means residual current device and this is a piece of equipment that will cut the electrical supply if it detects an imbalance in the current being sent and that being received (because there is a short circuit or someone has touched a live connector)
These are now built into most homes, sockets can have them built in or plug in types allow any equipment to be protected.
They should be tested regularly (and there is often a ‘test’ button for this purpose)
Test equipment
Oscilloscopes
Oscilloscopes show voltage and how is changes over time allowing engineers to ‘see’ what is happening.
They allow you to ‘freeze’ a signal and masure the voltages and times like you did with your circuit
They can also be used to see very and freeze short, rapidly changing voltages that may cause a circuit to malfunction
They show the voltage on the Y (up/down) axis and it can be adjusted to show the best scale
They show time on the X (left/right) axis and again it can be adjusted to show the best scale (sometimes called timebase)
Many oscioscopes are ‘dual trace’ meaning two signals can be shown but single trace are common and you can find 4 trace versions.
Some oscilloscopes are stand alone pieces of equipment, some connect to a computer to use it’s screen and circuit simulation software often includes them
Test equipment
Power supplies
In electronic engineering companies complex power supply equipment is uesd to power circuits being tested
These allow the circuit to be tested with different voltages to ensure they work as intended and maybe to test what would happen as the voltage drops such as from batteries that are becoming flat.
They also give accurate current readings to show how much current is being used and to ensure that the correct fuses can be chosen.
