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