EDDY Current probes
| Authors |
 |
|
|
G. Wache - Cegelec CNDT
P. Nourrisson - Cegelec CNDT
T. Garet |
It has been demonstrated in the past that a « reference
circuit » was able to produce eddy currents signatures
similar to whose obtained with the notches used for calibrating
the equipement [ 1 ], [ 2 ].
If the operator disposes of only one reference tube, with
artificial defects, to characterize the probes used in association
with the equipement, he can be surprised by sensitivity differences
observed on special events during the test, from one probe
to the other.
Among other reasons depending from the probe configuration
or manufacturing process , the two main listed below can explain
those differences :
- the test is generally performed by comparison between
the signal providing from the unknown defect and the one
providing from the reference notch used : the latter is
mainly affected by the nature of the material and the accuracy
of the machining process of the artificial defect.
- the coupling of the probe with the EC equipement is also
a source of discrepancy : the nature of the electronic bridge
used and the wire insuring the connection between the probe
and the generator can affect the signal by introducing a
filtering effect more or less significant.
Those injurious effects are attenuated by balancing the
probe with the equipement on the reference tube but in fact
they are still there, specially in absolute mode, and two
probes providing from different suppliers and qualified for
the process can lead to different responses.
By using a « reference circuit », it is possible
to reduce significantly the first effect and to evaluate the
bandwidth of the probe associated to the equipement independantly
of the reference tube : this paper shows examples of characterization
results obtained for condensors and steam generators axial
probes.
