|
Ohm's
Law
|
Impedance
|
Phase
Angle
|
Magnetic
Permeability
|
|
|
Where:
| Z |
= |
Impedance (ohm) |
| R |
= |
Resistance (ohm) |
| XL |
= |
Inductance Reactance(ohm) |
More Information
|
|
Where:
| m |
= |
Magnetic Permeability (Henries/meter) |
| B |
= |
Magnetic Flux Density (Tesla) |
| H |
= |
Magnetizing Force (Am/meter) |
|
|
Relative
Magnetic Permeability
|
Conductivity & Resistivity
|
Electrical
Conductivity
(%IACS)
|
Electrical
Conductivity
(%IACS) |
Where:
| mr |
= |
Relative Magnetic Permeability (dimensionless) |
| m |
= |
Any Given Magnetic Permeability (H/m) |
| mo |
= |
Magnetic Permeability in Free Space (H/m), which is 1.257 x 10-6 H/m |
More Information
|
Where:
| s |
= |
Electrical Conductivity
Siemens/m |
| r |
= |
Electrical Resistivity
(ohm-m) |
More Information
|
When resistivity is known 
Where:
| s%IACS |
= |
Electrical Conductivity
(% IACS) |
| r |
= |
Electrical Resistivity
(mohm-cm) |
| smS/cm |
= |
Electrical Conductivity
(mSiemens/cm) |
More Information
|
When conductivity in
S/m or mS/cm is known or
Where:
| s%IACS |
= |
Electrical Conductivity
(% IACS) |
| sS/m |
= |
Electrical Conductivity
(Siemens/meter) |
| smS/cm |
= |
Electrical Conductivity
(mSiemens/cm) |
More Information
|
|
Current Density
|
Standard Depth
of Penetration
|
Standard Depth
of Penetration
|
Standard Depth
of Penetration |
Where:
| Jx |
= |
Current Density (amps/m2) |
| Jo |
= |
Current Density at Surface (amps/m2) |
| e |
= |
Base Natural Log = 2.71828 |
| x |
= |
Distance Below Surface |
| d |
= |
Standard Depth of Penetration |
More Information
|
When electrical conductivity
(S/m) is known.
Where:
| d |
= |
Standard Depth of Penetration (m) |
| p |
= |
3.14 |
| f |
= |
Test Frequency (Hz) |
| m |
= |
Magnetic Permeability (H/m) (1.257 x 10-6 H/m for nonmagnetic mat'ls) |
| s |
= |
Electrical Conductivity
(Siemens/m) |
More Information
Depth of Pen Calculator
|
When electrical conductivity
(%IACS) is known.
In
mm |
 |
| In inches |
 |
Where:
| d |
= |
Standard Depth of Penetration (mm or in) |
| f |
= |
Test Frequency (Hz) |
| mr |
= |
Relative Magnetic Permeability (dimensionless) |
| s |
= |
Electrical Conductivity (%IACS) |
More Information
|
When electrical resistivity
(mohm-cm) is known.
In
mm |
 |
| In inches |
 |
Where:
| d |
= |
Standard Depth of Penetration (mm or in) |
| r |
= |
Electrical Resistivity
(mohm-cm) |
| f |
= |
Test Frequency (Hz) |
| mr |
= |
Relative Magnetic Permeability (dimensionless) |
More Information |
|
|
Eddy Current
Field Phase Lag
|
Eddy Current
Field
Phase Lag
|
Eddy Current
Field Phase Lag
|
Eddy Current
Field Phase Lag |
|
Where:
| q |
= |
Phase Lag (Rad or Degrees) |
| x |
= |
Distance Below Surface (in or mm) |
| d |
= |
Standard Depth of Penetration (in or mm) |
More Information
|
When electrical conductivity (S/m) is known.
Where:
| q |
= |
Phase Lag (degrees) |
| x |
= |
Distance Below Surface (m) |
| p |
= |
3.14 |
| f |
= |
Test Frequency (Hz) |
| mr |
= |
Relative Magnetic Permeability |
| s |
= |
Electrical Conductivity
(Siemens/m)
|
More Information
|
When electrical conductivity
(%IACS) is known.
In
mm |
 |
| In inches |
 |
Where:
| q |
= |
Phase Lag (degrees) |
| x |
= |
Distance Below Surface (mm) |
| f |
= |
Test Frequency (Hz) |
| mr |
= |
Relative Magnetic Permeability (dimensionless) |
| s |
= |
Electrical Conductivity (%IACS) |
More Information |
When electrical resistivity
(mohm-cm) is known.
In
mm |
 |
| In inches |
 |
Where:
| q |
= |
Phase Lag (degrees) |
| x |
= |
Distance Below Surface (inch) |
| r |
= |
Electrical Resistivity
(mohm-cm) |
| f |
= |
Test Frequency (Hz) |
| mr |
= |
Relative Magnetic Permeability (dimensionless) |
More Information
|
Standard Depth of Penetration and
Phase Angle
|
Material Thickness Requirement for
Resistivity or Conductivity Measurement
|
Frequency Selection
for Thickness Measurement of Thin Materials
|
Frequency Selection
for Flaw Detection
and Nonconductive
Coating Thickness Measurements |
Std.
Depth |
Relative
Strength
of EC
|
Phase Lag |
| 0 |
e0=100% |
0 rad = 0o |
| d |
e-1=37% |
1 rad = 57.3o |
| 2d |
e-2=14% |
2 rad = 114.6 o |
| 3d |
e-3=5% |
3 rad = 171.9 o |
| 4d |
e-4=2% |
4 rad = 229.2 o |
| 5d |
e-5=0.7% |
5 rad = 286.5 o |
|
When measuring resistivity or conductivity, the thickness of the material should be at least 3 times the depth of penetration to minimize material thickness effects
Where:
| t |
= |
Material Thickness |
| d |
= |
Standard Depth of Penetration |
More Information
|
Selecting a frequency that produces a standard depth of penetration that exceeds the material thickness by 25% will produce a phase angle of approximately 90obetween the liftoff signal and the material thickness change signal.
More Information
|
Defect Detection
A test frequency that puts the standard depth of penetration at about the expected depth of the defect will provide good phase separation between the defect and liftoff signals.
Nonconductive Coating Thickness Measurement
To minimize effects from the base metal the highest practical frequency should be used.
|
