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AV Fundies > AC Fundamentals > Flashcards

AC Fundamentals Flashcards

1
Q

3 main ways to measure amplitude?

A
  • Peak value
  • Peak to peak value
  • RMS value (DC equivalent)
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2
Q

3 basic measurements used when measuring an AC waveform?

A
  • Amplitude (Voltage, current and/or power)
  • Frequency (Time related / number of cycles in a given waveform that occurs in 1 second)
  • Phase angle (used to compare 2 sine waves of identical frequency)
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3
Q

Define peak?

A
  • Measured from the horizontal axis to either the maximum positive value or maximum negative value
  • 1 positive or negative half cycle
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4
Q

Define peak to peak?

A
  • Measurement between the maximum positive and the maximum negative portion of the waveform
  • Equal to 2 x peak value
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5
Q

Define RMS?

A
  • Root mean square
  • Average (0.707 of the peak value)
  • We see the RMS
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6
Q

Formula for VRMS?

A

VRMS = Vpk x 0.707
VRMS = V pk-pk divided by 2 x 0.707

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7
Q

Define cycle with regards to waveforms?

A
  • 1 full positive and 1 full negative in a horizontal fashion across the axis
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8
Q

Define frequency?

A
  • Represented by the letter f
  • Measure in Hz
  • Refers to the number of cycles completed in 1 second
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9
Q

Define period?

A
  • Represented by the letter t (time)
  • Measured in seconds (s)
  • The time it takes for a waveform to complete 1 cycle
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10
Q

Formula for frequency?

A

f = 1/t OR f = t to the power of -1

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11
Q

Formula for period?

A

t = 1/f OR t = f to the power of -1

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12
Q

Define phase angle?

A
  • The degree of separation between 2 waveforms of the same frequency
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13
Q

What does a Oscilloscope allow us to test?

A

Allows us to measure circuit values, such as:
- Voltage (pk=pk, pk and RMS)
- Frequency
- Period
- Phase angle

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14
Q

Oscilloscope construction?

A
  • Liquid crystal display (LCD)
  • Menu soft buttons
  • Menu option buttons
  • Channel 1, 2 and Maths settings
  • Horizontal settings
  • Miscellaneous buttons
  • Trigger settings
  • Probe connections
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15
Q

Probe construction?

A
  • Earth alligator clip
  • Probe tip (with witches hat extension)
  • Variable compensation capacitor
  • BNC connector
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16
Q

How to check calibration of oscilloscope?

A

Check the label is:
- In tact
- In date
- Signed
- Legible

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17
Q

Serviceability check for oscilloscope?

A
  • Physically check for damage and ensure the power lead has a ‘test-n-tag’ label attached (in-tact, in date, signed and legible)
  • Allow ‘power-on built-in-test’ to complete. Once this is finished, ensure all tests are displayed as passed
  • Probe calibration
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18
Q

Oscilloscope safety?

A
  • Ensure probes are connected to the testing equipment before connecting to the circuit under test
  • Ensure alligator clip is only ever connected to the earthing point
  • Ensure the maximum voltage is not exceeded
  • Ensure the maximum voltage of probe is not exceeded
  • Take care when disconnecting and connecting the oscilloscope
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19
Q

Phase angle voltmeter construction?

A
  • On / Off switch
  • Liquid crystal display (LCD)
  • Test port
  • Menu navigation buttons
  • Reference input
  • Signal input
  • Charging indicator LED
  • 5V DC input
  • Charged indicator LED
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20
Q

How to check calibration of a phase angle voltmeter?

A

Check the label is:
- In tact
- In date
- Signed
- Legible

21
Q

Serviceability test for phase angle voltmeter?

A
  • Turn on
  • Press the < button to start check and then connect the red and black leads into the reference ports and test ports
  • Press the > button. Ensure the frequency reads 400Hz and the voltage reads 4.8V pk-pk
  • Press the > button and then connect the red and black leads into the signal ports and test ports
  • Press the > button. Ensure the frequency reads 400Hz and the voltage reads 4.8V pk-pk
22
Q

3 different screen displays on the phase angle voltmeter?

A
  • Phase angle info screen
  • Signal info screen
  • Reference info screen
23
Q

3 types of transformer losess?

A
  • Eddy current losses (Current that circulates in the core - this loss is given off as heat and can be extremely dangerous)
  • Copper losses (Power lost due to resistance of the wire - this loss is given off as heat)
  • Hysteresis losses (Reversing magnetism of a transformers core will release energy in the form of heat)
24
Q

Construction of a transformer?

A
  • Primary and secondary winding and the core
  • Needs strong magnetic coupling (higher the magnetic coupling - the higher the induced voltage into the secondary coil, with as little loss as possible)
  • Both coils are wound around a core (creates a physical structure and magnetic path for the flux line)
25
Q

Formula for X L1

A

XL1 = 2 x pie x f x L

26
Q

Formula for X C1

A

XC1 = 1 / 2 x pie x f x L

27
Q

Formula for current total?

A

IT = VA / Z

28
Q

Define reactive power?
Formula for reactive power?

A
  • Power that does does not do work in the circuit - it is lazy
  • Applies to inductor and capacitors

Q = IT squared x X

29
Q

Define active power?
Formula for active power?

A

Power that is actually doing work in a circuit

P = I squared x R1

30
Q

Define apparent power?
Formula for apparent power?

A

Combination of active and reactive power

Pol (x, y) OR S = I squared x Z

31
Q

What makes up a power phasor diagram?

A

X axis - P (Active power)
Y axis - Q (Reactive power)

  • S (Apparent power)
  • Angle
32
Q

What makes up a voltage phasor diagram?

A

X axis - VR1
Y axis - VC1 or VL1 or VEQ

33
Q

What makes up an impedance phasor diagram?

A

X axis - R1
Y axis - XC1 or XL1 or XEQ

  • Z (impedance)
  • Angle
34
Q

Define mutual induction?

A

Changing current in one coil, induces EMF into the other

35
Q

The magnitude of the EMF is found to be directly proportional to 2 things. What are these?

A
  • Strength of the magnetic field
  • The speed that the magnetic field is expanding and collapsing
36
Q

Define the basic operations of a transformer?

A

A transformer will operate when an AC voltage is applied to its primary winding, then through mutual induction, an AC voltage is induced into the transformers secondary winding

37
Q

3 types of transformer cores?

A
  • Open core
  • Closed core
  • Shell core
38
Q

The amount of resistance in each winding depends on what 3 things?

A
  • Number of turns (length of the wire)
  • Thickness of the wire
  • The material that the wire is made of
39
Q

3 types of transformers?

A
  • Step up (Larger amount of voltage on the secondary)
  • Step down (Smaller amount of voltage in the secondary)
  • Isolation (1:1 ratio)
40
Q

What is the voltage / current relationship in a purely capacitive circuit?

A

Current leads voltage

41
Q

What is the voltage / current relationship in a purely inductive circuit?

A

Voltage leads current

42
Q

What is the voltage / current relationship in a purely resistive circuit?

A

In phase

43
Q

In a purely resistive circuit why does the power waveform always sit above the x axis?

A
  • Because all of the power is being used for a useful purpose
  • No waste
44
Q

In a purely reactive circuit, why does the power waveform continuously go positive to negative?

A

Power is being used both for a useful purpose and also being returned to the power supply

45
Q

3 types of materials used for transformers?

A
  • Iron
  • Ferrite
  • Air
46
Q

How many degrees are in 1 full wave cycle?

A

360 degrees

47
Q

Characteristics of an open core?

A
  • Poor magnetic coupling
  • Cheap
48
Q

Characteristics of a closed core?

A
  • Forms a loop independently wound - primary winding and secondary winding
  • Closed core
  • They do not touch
  • More efficient than the open core but still has losses
49
Q

Characteristics of a shell core?

A
  • Wound around each other
  • Tight magnetic coupling
  • Highest induced voltage
  • Best option for best performance and least loss

AV Fundies (11 decks)

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