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- since 1996 -

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Technical Discussions
Abhishek
Abhishek
02:15 Apr-18-2006
Selectable PRF feature

Is selectable PRF feature in single channel UFD useful for manual inspection? If so then, then grateful if someone could site a few examples or applications (in short) for instances where it is used?


    
 
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Mark potter
R & D
Sonemat Ltd., United Kingdom, Joined Sep 2007, 7

Mark potter

R & D
Sonemat Ltd.,
United Kingdom,
Joined Sep 2007
7
06:58 Apr-18-2006
Re: Selectable PRF feature
I've never payed much attention to PRF settings; I dont know how many flaw detectors allow you to alter them.

One obvious advantage if they were variable would be battery life, by selecting the lowest PRF you could get away with.

I dont know of any cases where the structures examined have been thick enough to require lowering of the PRF because the first echo comes back after the next pulse; usually structures that are thick would have too much attenuation anyway (although I am not experienced in field applications).

In theory, if you were using signal averaging a higher PRF could allow you to take an averaged reading faster, but averaging is still not commonly used in UFDs (and if it was, the speed of signal processing and analogue-digital conversion might be more limiting factors than the PRF, though these are always getting faster).


HTH,


Mark.


    
 
 Reply 
 
Thomas Murphy
Thomas Murphy
09:36 Apr-20-2006
Re: Selectable PRF feature
Hello all,

PRF can be very important in thick sections, Too high of a PRF can cause ghost echos. I have seen these reported. Too low of a PRF while a probe is moving, especially greater than 15cm/sec, might affect your data density to the point of not adequately covering the part. In other words PRF should be an machine setting called out in the procedure.

Regards,
Tom

having the probe ----------- Start Original Message -----------
: I've never payed much attention to PRF settings; I dont know how many flaw detectors allow you to alter them.
: One obvious advantage if they were variable would be battery life, by selecting the lowest PRF you could get away with.
: I dont know of any cases where the structures examined have been thick enough to require lowering of the PRF because the first echo comes back after the next pulse; usually structures that are thick would have too much attenuation anyway (although I am not experienced in field applications).
: In theory, if you were using signal averaging a higher PRF could allow you to take an averaged reading faster, but averaging is still not commonly used in UFDs (and if it was, the speed of signal processing and analogue-digital conversion might be more limiting factors than the PRF, though these are always getting faster).
:
: HTH,
:
: Mark.
------------ End Original Message ------------




    
 
 Reply 
 
Hermann Wüstenberg
R & D
BAM Berlin, Germany, Joined Nov 1998, 26

Hermann Wüstenberg

R & D
BAM Berlin,
Germany,
Joined Nov 1998
26
02:26 Apr-20-2006
Re: Selectable PRF feature
A selectable PRF is a feature a little bit more meaningful than suggested by the previous contributions. This has of course to be seen in connection with the problem of late returning echos appearing after the next transmission pulse, which is a common problem for fine grain steel components of larger dimensions, e.g. turbine or generator shafts, thickwalled pressure vessel components etc. The attenuation for those steel components is usually very low, which allows the interference by late returners. In order to verify such an interference, it would be very helpful to change the PRF. A shift of doubtful echos in an A-scan during the variation of the PRF is a clear hint for their origin.
Another fact should be considered in connection with the PRF: The first digital UFD (and many not very old types as well) had been and are even today equipped with AD-converters of fairly modest performances concerning sampling frequency and bit accuracy, which requires many more than one transmission pulse forthe digitization of one complete A-Scan. This has as a consequence that the actual physical PRF is rather difficult to estimate and of course can not be altered at will.
As a consequence one has to demand from the equipment producers a more clear position concerning the PRF variability of their products.

Hermann Wüstenberg





    
 
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