HARD SPOT INSPECTION TROLLEY - English -
Page 18/84
Operating and Maintenance Instructions
adaptaed from: https://app.box.com/s/c6qfgtuhfg1yd2ottrfum98x8jmg7rn3
| Hard spot inspection trolley • PLAMAT-M •
18201 |
|
| Operating and
Maintenance Instructions • V2.0 |
Fundamental principles
|
2.3 Incremental
permeability
The measuring principle
is based on the eddy current measurement. The small high frequent
field of the eddy current coil will be superimposed by the low frequent
magnetic field with high
field strength produced by the yoke. So the hysteresis curve will be
overlapped with a lot of
small reversible loops (Figure 7, top). The slope of these inner loops
µ∆ = B/H dependent on
the actual permeability in each point of the hysteresis loop. So the
impedance of the eddy
current measuring coil is changing while running through the hysteresis
loop.
Figure 7, bottom, shows the behavior of the incremental permeability µ∆
in dependency of the
low frequent exciting field.
Figure 7: Ferromagnetic hysteresis (top) and incremental permeability µA (bottom)
The following micro-magnetic parameters are considered for the incremental permeability analysis:
| DZmax [Ohm] |
maximum of incremental permeability |
| DZmean [Ohm] |
averaged incremental permeability |
| DZr [Ohm] |
incremental permeability at the remnant point |
| Ucdz [V] |
voltage at maximum incremental permeability |
| DU75dz [V] |
curve-widening at 75% signal peak |
| DU50dz [V] |
curve-widening at 50% signal peak |
| DU25dz [V] |
curve-widening at 25% signal peak |
| Rem [%] |
asymmetry of the incremental permeability curve |
Figure 8: Incremental permeability
| ROSEN and IZfP Page 18 of
84 |
Confidential! |
|
