|Ed Ginzel |
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1252
Universal DGS curves
I am looking for the source of the Universal DGS curves.
I have seen the General curves in many locations including the EN 583-2 (which replaces the DIN 54127-1) and several training manuals including the DGZfP UT2e.
But nowhere do I see the algorithms used to define the curves. The inverse square law for far zone decays of the disk reflectors is clear enough, but some of the peak amplitudes for the Disk reflectors (G >0.2) do not coincide with N but get shifted towards 2N.
The "estimates" for the near zone are another mystery.
|Hermann Wüstenberg |
R & D
BAM Berlin, Germany, Joined Nov 1998, 26
Re: Universal DGS curves ----------- Start Original Message -----------
: I am looking for the source of the Universal DGS curves.
: I have seen the General curves in many locations including the EN 583-2 (which replaces the DIN 54127-1) and several training manuals including the DGZfP UT2e.
: But nowhere do I see the algorithms used to define the curves. The inverse square law for far zone decays of the disk reflectors is clear enough, but some of the peak amplitudes for the Disk reflectors (G >0.2) do not coincide with N but get shifted towards 2N.
: The "estimates" for the near zone are another mystery.
------------ End Original Message ------------
The universal DGS diagram had been introduced in Germany between 1968 and 1973, in order to be used for ultrasonic weld inspection with angle beam probes as a tool for the sensitivity setting and the definition of recording and acceptance thresholds. The structure of this diagram in the nearfield zone is based on a compromise derived frommeasurements and calculations for normal incident and angle beam probes of various transducer shape, size and frequency. According to the publications of this time one has considered the curves in the nearfield range for distances smaller than 1.5x No (No = Nearfield length) as sufficiently precise (e.g. not more than 1,5 dB deviation below this distance). A first report on the basic work for the definition of this universal DGS diagram has been presented May 1969 during the annual conference of the german NDT society DGZfP at Freudenstadt.
(H. Wüstenberg, E. Mundry: Beitrag zum AVG-Diagramm für Winkelprüfköpfe) This report is still available at the BAM Berlin. It seems that an English translation had been foreseen for a Working group of the IIW with the document Nr. IIW Document WG-Vc 2/71 (1971).
Since the nearfield length is a key value for the application of an universal DGS-diagram, this report gives an early approximation for the nearfield length of angle beam probes with rectangular transducers, which later on has been modified based on publications from U. Schlengermann, J. Marini , H. Wüstenberg as e.g. cited in
„Zur Auswahl der Membranformen bei Winkelprüfköpfen für die Ultraschallprüfung,“
Wüstenberg, H., Schulz, E., Möhrle, W., Kutzner, J.:
Materialprüfung 18 Nr. 7, Juli 1976, p. 223-230
and is now applied as follows:
No = 1/(pi*lambda) *(a*a +b*b) * ( 0,78 - 0,27*(a/b)) with a < b
For the total soundpath Stot= Sobj +Sequ one has to take into account the delay path within the wedge as a so-called soundfield equivalent path
( Sequ = Swedge*Cwedge/Cobj)
With the effective diameter of an equivalent circular transducer derived from the above mentioned nearfield length ( Deff = 2*SQRT(l*No) ) one is able to use the universal DGS-diagram for sensitivity setting and echo amplitude evaluation purposes.
There had been several commercial approaches to describe the universal DGS-diagram and its curves by simple mathematical formula. Information about those efforts may be asked from the producers of UT equipments. (e.g. GE/Krautkrämer or Olympus/Panametrics)
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