Random Q's Flashcards
1
Q
Who discovered Eddy Currents?
A
Leon Foucault
2
Q
What symbol is commonly used to express conductivity?
A
DELTA “fancy o”
3
Q
What symbol is commonly used to express permeability?
A
MU “micro symbol”
4
Q
What is the term used to define a material that has a permeability larger than 1?
A
Ferromagnetic
5
Q
What symbol is commonly used to signify inductance?
A
L
6
Q
What supplies the AC required for Eddy Current testing?
A
Sine wave oscillator
7
Q
All materials have a characteristic resistance to the flow of electricity. What are materials with low resistance called?
A
Conductors
8
Q
Pure annealed copper has a resistivity of 1.7241 micro ohms per cm at 20 degrees Celsius. How do you convert this value to 100% IACS value?
A
Divide by 0.017241
9
Q
What discontinuity is most likely to be found in a rolled bar stock?
A
Seams
10
Q
A fatigue crack would be defined as what type of defect?
A
Service defect
11
Q
Eddy Current testing is generally used to inspect what type of materials?
A
Conductors
12
Q
How do Eddy Currents travel?
A
In closed paths
13
Q
At any given moment, a spring loaded internal probe can inspect how much of the material?
A
An area roughly defined by the size of the probe coil
14
Q
What are some products commonly tested with an encircling probe?
A
Rods, tubes and wire
15
Q
Who discovered electromagnetic induction?
A
Michael faraday
16
Q
What type of materials are easiest to test with Eddy Current?
A
Paramagnetic and diamagnetic
17
Q
What type of wave is used in Eddy Current as opposed to UT?
A
Electromagnetic wave instead of a mechanical wave
18
Q
What is the most common use of ECT?
A
- Crack and corrosion detecting**
- Material sorting
- Coating thickness testing
19
Q
What is a limitation of Eddy Current?
A
Only can be conducted in electrically conductive materials
20
Q
The depth for subsurface flaws will be limited to what?
A
10 mm or less
21
Q
What type of method is ET?
A
Comparative
22
Q
What is magnetic flux? And what units is it expressed in?
A
Totally number of lines of force existing in a magnetic circuit.
Units: Weber and maxwell
23
Q
What is magnetic flux density?
A
Strength of magnetic field expressed in number of flux lines passing traversal through a unit area
24
Q
What are the two basic types of solids?
A
- Crystalline (typical metals)
2. Amorphous (mainly viscous liquids)
25
How are north and south polls determined?
By the way the electrons are spinning
26
A high carbon content means what did permeability?
Low permeability
27
The flow of electrons is measured in what unit?
Amperes
28
Electromotive Force (EMF) is measured in what units?
Volts
29
What is the definition of resistance?
The OPPOSITION to the flow of electrons within an electric circuit
30
Electricity always takes the path of....
Least resistance
31
What does the number of electrons in the valence shell of an atom say about its conductivity?
The least number of electrons means a great conductor
| Full valence shell = non-conductive
32
The symbol for resistance is what?
OMEGA “ohm”
33
What leads and what lags?
Voltage leads and current (amperage) lags
34
What type of couplant is used in ECT?
Magnetic couplant
35
What is an ammeter used for?
To indicate how many AMPS of current are flowing in an electrical circuit
36
What does a voltmeter measure?
EMF/volts in a circuit
37
What is an Ohm meter used to measure?
Electrical resistance in a circuit
38
What is electromagnetic induction?
Inducing an electrical current in a conductor by bringing conductor in proximity with a magnetic field
39
What is induction measured in?
Henries
40
What is self inductance?
Inductance occurring with a current containing a coil or solenoid
41
What would be the worst core material to use?
Diamagnetic (copper)
42
What is mutual inductance?
Electrical relationship that occurs between 2 electrical circuits coupled by moving magnetic fields
43
What is impedance?**
The TOTAL OPPOSITION to primary current flow
44
Hertz is used instead of...
Cycles per second
45
What is inductive reactance?
Effect that causes the current to lag behind the voltage
46
What is the best and worst conductive?
Silver is the best and titanium is the worst
47
What does Ohm’s Law state?
The resistance in a circuit is equal to the voltage divided by current
48
Why can’t resistance and inductive reactance be added directly?
Their effect on voltage is out of phase
49
What is the easiest way to combine resistance and inductive reactance?
Vector addition
50
What does the vector direction and length represent?
Length represents a value and direction represents its phase relationship
51
What is alpha?
The phase angle of the impedance vector
52
As resistance decreases, what happens to impedance and phase angle?
Impedance value increases and phase angle decreases
53
What happens to the phase angle as inductive reactance increases?
Phase angle increases
54
Change in voltage or frequency does NOT affect what?
Resistance
| Inductive reactance is affect by frequency changes
55
Inductance value is determined by what?
Size, shape and number of coil turns
56
Currents and magnetic fields involved are constantly changing but __________ always stays the same.
Phase relationship between each
57
Lift off is considered what type of factor?
Dimensional factor
58
What is the resistivity symbol and what is it expressed in?
Symbol is RHO (p) and it’s expressed in micro ohm centimetres
59
What are the 3 basic coils?
1. Probe coils (surface, flat or pancake)
2. Bobbin
3. Encircling
60
The spring mechanism in a probe coil is used to...
Minimize lift off
61
The coil is secured with what to prevent electrical shorts?
Epoxy
62
What is an advantage of shielding?
Can perform inspection near edge of sample
63
What 3 main factors cause resistance?
1. Cross sectional area
2. Length
3. Resistivity (composition) of material
64
Lift off is utilized in what?
Fill factor
65
What happens to impedance as frequency increases?
Increases
66
What types of defects are easiest to see when using an encircling coil?
Longitudinal defects
67
What are the 2 types of differential coils?
1. Self comparison differential
| 2. External reference differential
68
What are 4 factors that the absolute coil method measures?
1. Conductivity
2. Permeability
3. Dimensions
4. Hardness
69
What do hybrid coils consist of?
Excitation AND receiving coil
70
What are 3 other names for a hybrid coil?
1. Driver/pickup
2. Through transmission
3. Primary-secondary coil
71
Phase discrimination uses angles to differentiate between what?
XL and R
72
What are the 5 basic components?
1. Excitation
2. Modulation
3. Signal Prep
4. Demodulation & Analysis Control
5. Signal Display
73
Where do changes in brightness, contrast, phase rotation and screen persist happen?
Signal display
74
Which component occurs at the primary and secondary magnetic field interface?
Modulation circuitry
75
What component operates the power generator/oscillator?
Excitation
76
In which component involves sampling and speed of inspection?
Demodulation & Analysis Control
77
In what component do you balance networks and gain & dB control?
Signal Prep
78
What is the sixth optional component?
Alarms & Data Recorders
79
What are 4 types of displays and something brief about each?
1. Flying dot - most current
2. Needle/Meter - most basic
3. Elliptical - CRT screen
4. Digital/Numeric - conductivity
80
Hand heat can change what variable of the the coil?
Resistance
81
What does a armiture wear face entail?
Coated with a resin
82
What type of probe has an adjacent collar to maintain position when the probe has been inserted inside test piece?
Manual rotating bore probe
83
Why is a spot probe good for conductivity measuring?
It can’t wobble
84
What does a collar help to minimize?
Edge effect and keeps probe at a specific height
85
At what orientation are the eddy currents to the coil and magnetic field?
Parallel to the coil and 90 degrees to the magnetic field
86
How do eddy currents flow in an encircling coil?
Circumferentially
87
What are the 2 major differences in conductivity models?
1. Signal generation:
a) fixed OR
b) variable
2. Output style
a) analog (meter) OR
b) digital (LCD)
88
With a “fixed” frequency device, what do you know?
The material thickness that should be inspected because you also know the depth of penetration
89
How do you change the frequency in a “variable” device?
You can’t, it changes internally during calibration
90
What is assigned a relative permeability of one?
Aluminum
91
The phase is?
The direction the change occurred in
92
Older versions of CRT test instruments relied on what?
Focused beams of electrons being emitted by a “gun”
93
What is a primary advantage of a single frequency device?
Very portable and don’t need direct access to AC power supply
94
What can you set channels for in a multi frequency device?
Only detects changes to a certain depth
95
Multi frequency can help reduce signal loss due to what?
“Ganging” several coils on the same circuit
96
What degree “out of phase” is a good ratio to mix a new channel on a multi-parameter device?
90 degrees
97
What are the two options that systems can be?
1. Multitasked
| 2. Dedicated
98
What are the 3 main categories of test equipment?
1. Conductivity testers
2. Crack detectors
3. Multi purpose
99
Phase Angle Discrimination Module circuitry is used in what type of detector?
Multi purpose
100
What did Phase Angle Discrimination Module circuitry allow CRT’s to do?
Detect conductivity, cracks PLUS measure thickness, hardness and heat treatment
(Old elliptical signals displays were then replaced with flying vector dot displays)
101
A hybrid coil is not suited for what type of discontinuities and testing?
Not suitable for small surface inspections or conductivity testing
102
An increase in magnetic permeability will do what to the noise?
Increase it
103
Why would you choose an automatic bolt hole scanner over a manual one?
It’s spinning so fast that you won’t see deviation between layers of material (which reduces sensitivity)
104
What are the 2 other names that a “flying vector dot” can be called?
Multipurpose or phase analysis
105
What is the biggest disadvantage of a crack detector?
Can’t measure variables independently
106
Frequencies for surface inspection is generally is what range?
100 kHz - 2 MHz
107
What frequencies are generally used for subsurface inspections?
500 Hz - 10 kHz
108
We want no less than what percentage of fill factor?
80%
109
How do you calculate fill factor?
Diameter of part divided by diameter of coil
110
How many standard depths of penetration can you see on an EC machine?
Five
111
Which coil is the most sensitive?
Hybrid/Reflection coil
