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- since 1996 -
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Technical Discussions
Mario Belo
NDT Inspection
Trenes Buenos Aires, Argentina, Joined Jan 2000, 7

Mario Belo

NDT Inspection
Trenes Buenos Aires,
Argentina,
Joined Jan 2000
7
00:43 Mar-08-2001
Attenuation calculation

Dear experts:

To calculate attenuation with angular probes I have to use the Pitch-Catch technique obtaining two echoes(different measures) of the same piece.

Am I proceeding the right way?

Do I have to do this with the control set for 2 probes?

Kind regards.

Mario bello

Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 180

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
180
00:55 Mar-09-2001
Re: Attenuation calculation
reply by Udo Schlengermann
:

Obviously you should use two angle beam probes of same type and angle in separate transmitter receiver mode, i.e. one probe is transmitting, the other is receiving.
Position the probes facing each other on a plate and take an echo at a direct V-path between the probes. Then increase distance till you get a W-path (double V) and take another reading.
The path difference is a single V for the angle used.
So the dB-difference between the two readings give you a measure of attenuation in dB/mm sound travel path.
This technique is not exact, because there are other losses which must be compensated. If both readings are in the farfield of the probes you have to compensate the diffraction losses by 6 dB.
And this technique works only with total reflection, i.e. with angles of 45°. With other angles you get mode conversion and therefore additional losses which are not caused by attenuation.

Kind regards
Udo Schlengermann

: Dear experts:
.
: To calculate attenuation with angular probes I have to use the Pitch-Catch technique obtaining two echoes(different measures) of the same piece.
.
: Am I proceeding the right way?
.
: Do I have to do this with the control set for 2 probes?
.
: Kind regards.
.
:
: Mario bello
.

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