7C Flashcards
4 electrical variables to be measured
Voltage, Current, Resistance, Power
Advantages of analogue meters over digital
Easier to identify trends with the sweeping needle
Analogue meter doesn’t read ‘ghost’ voltages
explain how the d’Arsonval meter works
A coil moves in proportion to a magnetic field created by the current you are measuring. The coil is connected to a needle which indicates on the analogue meter. A spring is attached to the needle and coil which brings it back to neutral when no current is applied
Ammeter is connected to the test load in series, however internally the ammeter measures in parallel. T or F
True
DC ammeters are not sensitive to current direction? T or F
False
Shunts are connected in series or parallel to ammeters
Parallel
How does a multi range ammeter differ to a normal ammeter
A multi range ammeter has multiple shunts with varying resistances. You can manually select the resistance you want so you can measure a range of current ratings without cooking the device
For multi range ammeters you should always start at the lowest current range and work your way up to the required range to not blow up the machine. T or F
False
Voltmeters should be connected in parallel. T or F
True
What is the difference between a DC and AC meter?
An AC meter has a rectifier to convert AC power to DC for reading
What current does a safety ohmmeter use
0.5mA
How must you calibrate an Ohmmeter
Short the ohmmeter and then adjust the rheostat to get a ‘zero’ reading
characteristics of a megohmmeter
A regular ohmmeter with a step up transformer to greatly increase voltage. low current
What is the point of a Current Transformer
to measure current flow at levels which would otherwise be beyond the range of the meter
Benefits of a clamp meter
you can conveniently measure the current of any wire by enclosing the clamp meter around the wire
Generally, how often is a calibration required
1 year
Logic probes are used for:
trouble shooting in logic circuits by indicating whether certain parts of the circuit are hi or low
What is RMS
a way to compare DC to AC power. It is the point of an AC wave where the power output is the same as DC power. It is always 0.707x the AC peak
Signal generators are used to;
test and align all types of transmitters and receivers
What is an attenuator
Device that reduces the amplitude or power of a signal without distorting the waveform
How does a time domain reflectometer measure where along the cable the error is?
the time taken for a signal to reach the end of a known length of cable is a known value. When a signal is received in a shorter amount of time, the speed of light and time to receive this signal is used to figure out how far away from the measurement the error in cable is.
Pitot static testers;
consists of applying pressure into the pitot tubes at a controlled rate to check whether the pitot tubes are measuring and reading data correctly
Turbine temperature tester works by
applying a temperature to the thermocouples to ensure they are reading data correctly
Fuel quantity indication test sets work by
creating a fake capacitance signal on fuel sensing probes
Why should you ensure Fuel quantity indication test sets are grounded
fuel and sparks do not mix
Loop resistance testers analyses circuits of cables by;
measuring resistance at two locations within a cable loop to check for corrosion
Circuit tests normally include
Bonding testing
Continuity testing
Insulation resistance testing
Functional testing
If arcing is detected you should
check bonding straps for corrosion
How to test a bonding meter
Short the three prongs on both probes to obtain a zero reading
Short two prongs of the double prong probe to obtain full deflection
For general electrical bonding, what is the max lead resistance
0.1 Ohms
Why should you use copper terminations on copper wire and aluminium terminations on aluminium wire?
to prevent dissimilar metal corrosion
What class crimping tools, lugs and splices should not be used on aircraft
Class 2
How do hand crimping tools prevent half crimps
Most have a self locking ratchet which prevents the tool from opening until the crimp is complete
Order of colour determining wire gauge sizes
Yellow (smallest), Red, Blue (largest)
What is the point of the abrasive compound inside an aluminium wire termination
during crimping, the compound releases and cleans the oxide film on the aluminium to avoid corrosion
What should you inspect a crimped termination for?
Crimp indent centred on the terminal lug barrel
Indent in line with the barrel
Terminal lug not cracked
Terminal lug insulation not cracked
Insulation grip crimped
What are splices used for
When a wire splits in the middle and needs to be reconnected
Standard practices for splicing
splices must be visable for future inspection
on bundles of wires requiring multiple splices, space the splices out to ensure bundle size doesn’t increase
usually only one splice per wire
should not be used within 12in of termination
What is the max bend radius of a coax cable
6 times the diameter of the cable
Max number of wires in a bundle
75 or 5cm diameter
Max distance between cable identifiers
15in
Max bend radius of a regular cable, supported and unsupported
10x diameter unsupported
3x diameter supported
What should be installed when a wire passes through a bulkhead or wall cutout with less than 1cm clearance
a gommet around the wall
Wires must be be spaced as far away as possible from plumbing lines. T or F
True
The purpose of flux is to
remove oxidation during soldering
Hard solders are used for
Situations where greater mechanical strength or exposure to higher temps is required (e.g. Thermocouples)
Flux core solder is
A solder wire with a channel of rosin flux inside, providing a convenient and controlled flux application
Heat sinks are used for
absorbing unwanted conducted heat before it reaches the hear sensitive circuitry around the joint you’re soldering
How long do you have to clean flux residue post soldering
1 hour
What is the most efficient soldering iron temp for general use
240-270
