Eddy current Flashcards
which component in an eddy current inspection system provides current to the test coil?
oscillator
which component converts changes in eddy current magnitude and distribution into signals to be processed?
bridge circuit
what effect does high conductivity have on eddy current depth of penetration?
reduced depth of penetration
what’s the term for signal changes caused by the eddy current field intercepting a corner of a part?
edge effect
if all other factors remain unchanged what effect does higher frequency have on eddy current depth of penetrations?
shallower depth of penetration
what’s the definition of the standard depth of penetration of eddy currents?
point where eddy current strength drops to 36.8% of surface strength
how many times deeper than the standard depth of penetration is the effective depth of penetration?
3 times
what’s the desirable signal-to-noise ratio for flaw detection?
3 to 1
how can you eliminate line voltage fluctuations that may be affecting your signal-to-noise ratio?
switch to a battery powered unit
based on application, what are the three general classifications of eddy current probes?
- surface 2. Inside diameter (ID) 3. Encircling
what characteristics of a probe determine the surface area inspected?
diameter of the probe and any shielding in the probe
what type of eddy current probes concentrate the field directly under the coil and overcome many of the problems associated with edge effect?
shielded probes
what’s the definition of impedance?
total opposition to the flow of AC in an eddy current coil
Where do phase angles form?
where the sine waves, representing 2 elements of AC, cross
What does the line (formed on a CRT) between the dot with the probe off the part (Po) and the dot when the probe is placed on the part (P1) represent?
lift off
how can you configure impedance plane instruments to measure amplitude changes only?
calibrate the unit in the sweep display mode
how much operating time remains when the low-battery indicator indications appears?
1/2 hour
Which control on the Nortec 2000 is used to adjust numerical parameters or the display appearance, depending on the function selected?
smartknob
What key is pressed on the Nortec 2000 to display information to adjust the basic operating conditions of the unit, such as frequency or gain?
MAIN/FILTER key
Which function key will activate the bolt hole scanner controls?
SETUP/SPECIAL key
Which of the two immediate executions keys is used to execute an instrument operation or respond to a prompt?
ENTER key
Which menu soft key would you press after the MAIN key in order to change horizontal and vertical gain together?
press gain menu soft key after you’ve pressed the MAIN key
What is the operating frequency range of the Nortec 2000?
100 Hz to 12Mhz
what two ways can the phase angle or rotation be set?
using the smartknob or INC/DEC keys
Which two keys must be pressed before you can adjust the sweep with the smartknob?
first the DISP key then the DISPLAY key
From which menu would you start to reset the unit to factory default settings?
SETUP menu
Where should the flying dot be located after nulling is complete?
50 percent full screen height and 50% full screen width
What must you make sure of when placing the probe on the crack standard?
make sure probe is on a good area away from any cracks
When is the sensitivity check required?
when using the Air Force General Purpose reference standard
during surface flaw detection, how would you estimate a discontinuity’s size?
by comparing it’s indication with your crack standard’s indication
how should you scan a part to avoid missing small cracks?
move the probe perpendicular to the probable direction of defects
what materials should not be used to make eddy current fixtures?
conductive materials
what happens to an eddy current signal from defects of the same size as one of the defects increases in depth below the surface?
it decreases
What is the most important dimension of a crack?
depth
What’s the most important fact about the AF general Purpose Eddy Current Standard?
it is the only authorized eddy current standard to be used without a specific waiver
what are three examples of artificial defects in eddy current standards?
- EDM 2. Saw 3. Machine notches
what is the primary purpose of any standard?
provide you with a uniform response directly related to the condition or material property you are detecting or measuring
What two fators must be tightly controlled during manufacture of an eddy current standard?
material specification and fabrication requirements
What system is conductivity measurement based on?
International Annealed Copper Standard (IACS)
What shim thickness is used when calibrating the Nortec 2000 liftoff for conductivity testing?
0.004 inch
What do you isolate when you look for specified amount of conductivity change?
heat damage
What temperature difference between the standards and the part will prevent your from performing conductivity testing?
10 degrees F or more
What must you do if during conductivity testing you discover the calibration of the instrument is no longer valid?
recheck all readings taken since last calibration once unit is recalibrated
